Any of the more than 100 known substances (of which 93 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter; SYN. element.
Alternate name for element.
Sinonimi: H | atomic number 1
ETYM Hydro-, 1 + -gen: cf. French hydrogčne. So called because water is generated by its combustion. Related to Hydra.
A nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe; SYN. H, atomic number 1.
Colorless, odorless, gaseous, nonmetallic element, symbol H, atomic number 1, atomic weight 1.00797. It is the lightest of all the elements and occurs on Earth chiefly in combination with oxygen as water. Hydrogen is the most abundant element in the universe, where it accounts for 93% of the total number of atoms and 76% of the total mass. It is a component of most stars, including the Sun, whose heat and light are produced through the nuclear-fusion process that converts hydrogen into helium. When subjected to a pressure 500,000 times greater than that of the Earth's atmosphere, hydrogen becomes a solid with metallic properties, as in one of the inner zones of Jupiter. Hydrogen's common and industrial uses include the hardening of oils and fats by hydrogenation, the creation of high-temperature flames for welding, and as rocket fuel. It has been proposed as a fuel for road vehicles.
Its isotopes deuterium and tritium (half-life 12.5 years) are used in nuclear weapons, and deuterons (deuterium nuclei) are used in synthesizing elements. The element's name refers to the generation of water by the combustion of hydrogen, and was coined in 1787 by French chemist Louis Guyton de Morveau (1737–1816).
Sinonimi: He | atomic number 2
Non-inflammable, lighter-than-air, inert gas.
A very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas); SYN. He, atomic number 2.
Colorless, odorless, gaseous, nonmetallic element, symbol He, atomic number 2, atomic weight 4.0026. It is grouped with the inert gases, is nonreactive, and forms no compounds. It is the second-most abundant element (after hydrogen) in the universe, and has the lowest boiling (-268.9şC/-452şF) and melting points (-272.2şC/-458şF) of all the elements. It is present in small quantities in the Earth's atmosphere from gases issuing from radioactive elements (from alpha decay) in the Earth's crust; after hydrogen it is the second-lightest element.
Helium is a component of most stars, including the Sun, where the nuclear-fusion process converts hydrogen into helium with the production of heat and light. It is obtained by compression and fractionation of naturally occurring gases. It is used for inflating balloons and as a dilutant for oxygen in deep-sea breathing systems. Liquid helium is used extensively in low-temperature physics (cryogenics).
Sinonimi: Li | atomic number 3
ETYM New Lat., from Greek litheios of stone, from lithos stone.
Soft, ductile, silver-white, metallic element, symbol Li, atomic number 3, atomic weight 6.941. It is one of the alkali metals, has a very low density (far less than most woods), and floats on water (specific gravity 0.57); it is the lightest of all metals. Lithium is used to harden alloys, and in batteries; its compounds are used in medicine to treat manic depression.
Lithium was named in 1818 by Swedish chemist Jöns Berzelius, having been discovered the previous year by his student Johan A Arfwedson (1792–1841). Berzelius named it after “stone” because it is found in most igneous rocks and many mineral springs.
A soft silver-white univalent element of the alkali metal group; the lightest metal known; occurs in several minerals; SYN. Li, atomic number 3.
ETYM New Lat.
A light strong brittle gray toxic bivalent metallic element; SYN. Be, glucinium, atomic number 4.
Hard, white metal used in alloys, occurring as an element only in compounds.
Hard, light-weight, silver-white, metallic element, symbol Be, atomic number 4, atomic weight 9.012. It is one of the alkaline-earth metals, with chemical properties similar to those of magnesium; in nature it is found only in combination with other elements. It is used to make sturdy, light alloys and to control the speed of neutrons in nuclear reactors. Beryllium oxide was discovered in 1798 by French chemist Louis-Nicolas Vauquelin (1763–1829), but the element was not isolated until 1828, by Friedrich Wöhler and Antoine-Alexandre-Brutus Bussy independently.
In 1992 large amounts of beryllium were unexpectedly discovered in six old stars in the Milky Way.
The name comes from Latin beryllus.
Sinonimi: B | atomic number 5
Non-metallic, non-fusible element, found in borax, etc.
Nonmetallic element, symbol B, atomic number 5, relative atomic mass 10.811. In nature it is found only in compounds, as with sodium and oxygen in borax. It exists in two allotropic forms (see allotropy): brown amorphous powder and very hard, brilliant crystals. Its compounds are used in the preparation of boric acid, water softeners, soaps, enamels, glass, and pottery glazes. In alloys it is used to harden steel. Because it absorbs slow neutrons, it is used to make boron carbide control rods for nuclear reactors. It is a necessary trace element in the human diet. The element was named by Humphry Davy, who isolated it 1808, from borax + -on, as in carbon.
A trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder; SYN. B, atomic number 5.
Sinonimi: C | atomic number 6
ETYM French carbone, from Latin carbo coal; cf. Skr. çrâ to cook.
An abundant nonmetallic tetravalent element occurring in three allotropic forms: amorphous carbon and graphite and diamond; occurs in all organic compounds; SYN. C, atomic number 6.
Nonmetallic element, symbol C, atomic number 6, relative atomic mass 12.011. It occurs on its own as diamond, graphite, and as fullerenes (the allotropes), as compounds in carbonaceous rocks such as chalk and limestone, as carbon dioxide in the atmosphere, as hydrocarbons in petroleum, coal, and natural gas, and as a constituent of all organic substances.
In its amorphous form, it is familiar as coal, charcoal, and soot. The atoms of carbon can link with one another in rings or chains, giving rise to innumerable complex compounds. Of the inorganic carbon compounds, the chief ones are carbon dioxide, a colorless gas formed when carbon is burned in an adequate supply of air; and carbon monoxide (CO), formed when carbon is oxidized in a limited supply of air. Carbon disulfide (CS2) is a dense liquid with a sweetish odor. Another group of compounds is the carbon halides, including carbon tetrachloride (tetrachloromethane, CCl4). When added to steel, carbon forms a wide range of alloys with useful properties. In pure form, it is used as a moderator in nuclear reactors; as colloidal graphite it is a good lubricant and, when deposited on a surface in a vacuum, obviates photoelectric and secondary emission of electrons. Carbon is used as a fuel in the form of coal or coke. The radioactive isotope carbon-14 (half-life 5,730 years) is used as a tracer in biological rese.
Arch. Analysis of interstellar dust has led to the discovery of discrete carbon molecules, each containing 60 carbon atoms. The C60 molecules have been named buckminsterfullerenes because of their structural similarity to the geodesic domes designed by US architect and engineer Buckminster Fuller.
The element has the following characteristic reactions. with air or oxygen It burns on heating to form carbon dioxide in excess air, or carbon monoxide in a limited supply of air.
C + O2 ® CO2 DH = -394 kJ mol-1.
2C + O2 ® 2CO.
With metal oxides.
It reduces many metal oxides at high temperatures. Fe2O3 + 3C ® 2Fe + 3CO with steam It forms water gas (a cheap, useful, industrial fuel) when steam is passed over white-hot coke.
C + H2O ® CO + H2.
With concentrated acids.
With hot, concentrated sulfuric or nitric acids it forms carbon dioxide.
Sinonimi: O | atomic number 8
ETYM French oxygčne, from Greek oxys sharp, acid + root of genesis birth. So called because originally supposed to be an essential part of every acid.
Colorless, odorless, tasteless, nonmetallic, gaseous element, symbol O, atomic number 8, atomic weight 15.9994. It is the most abundant element in the Earth's crust (almost 50% by mass), forms about 21% by volume of the atmosphere, and is present in combined form in water and many other substances. Oxygen is a by-product of photosynthesis and the basis for respiration in plants and animals.
Oxygen is very reactive and combines with all other elements except the inert gases and fluorine. It is present in carbon dioxide, silicon dioxide (quartz), iron ore, calcium carbonate (limestone). In nature it exists as a molecule composed of two atoms (O2); single atoms of oxygen are very short-lived owing to their reactivity. They can be produced in electric sparks and by the Sun’s ultraviolet radiation in space, where they rapidly combine with molecular oxygen to form ozone (an allotrope of oxygen).
Oxygen is obtained for industrial use by the fractional distillation of liquid air, by the electrolysis of water, or by heating manganese(IV) oxide with potassium chlorate. It is essential for combustion, and is used with ethyne (acetylene) in high-temperature oxyacetylene welding and cutting torches.
The element was first identified by English chemist Joseph Priestley 1774 and independently in the same year by Swedish chemist Karl Scheel. It was named by French chemist Antoine Lavoisier 1777.
A nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 28 percent of the atmosphere by volume; the most abundant element in the earth's crust; SYN. O, atomic number 8.
Sinonimi: F | atomic number 9
ETYM New Lat. fluorina: cf. German fluorin, French fluorine. So called from its occurrence in the mineral fluorite.
A nonmetallic univalent element; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite; SYN. F, atomic number 9.
Pale yellow, gaseous, nonmetallic element, symbol F, atomic number 9, atomic weight 19. It is the first member of the halogen group of elements, and is pungent, poisonous, and highly reactive, uniting directly with nearly all the elements. It occurs naturally as the minerals fluorite (CaF2) and cryolite (Na3AlF6). Hydrogen fluoride is used in etching glass, and the freons, which all contain fluorine, are widely used as refrigerants.
Fluorine was discovered by the Swedish chemist Karl Scheele in 1771 and isolated by the French chemist Henri Moissan in 1886.
Combined with uranium as UF6, it is used in the separation of uranium isotopes.
Sinonimi: Ne | atomic number 10
Colorless, odorless, nonmetallic, gaseous element, symbol Ne, atomic number 10, atomic weight 20.183. It is grouped with the inert gases, is non-reactive, and forms no compounds. It occurs in small quantities in the Earth's atmosphere.
Tubes containing neon are used in electric advertising signs, giving off a fiery red glow; it is also used in lasers. Neon was discovered by Scottish chemist William Ramsay and the Englishman Morris Travers.
A colorless odorless gaseous element that give a red glow in a vacuum tube; one of the six inert gasses; occurs in the air in small amounts; SYN. Ne, atomic number 10.
ETYM New Lat., fromE. soda.
Soft, waxlike, silver-white, metallic element, symbol Na (from Latin natrium), atomic number 11, relative atomic mass 22.898. It is one of the alkali metals and has a very low density, being light enough to float on water. It is the sixth-most abundant element (the fourth-most abundant metal) in the Earth’s crust. Sodium is highly reactive, oxidizing rapidly when exposed to air and reacting violently with water. Its most familiar compound is sodium chloride (common salt), which occurs naturally in the oceans and in salt deposits left by dried-up ancient seas.
Other sodium compounds are of great industrial importance and thousands of tons are manufactured annually. Sodium functions with potassium on the cellular level to make possible neuronal transmission, and so it is an essential nutrient for animals. It was named in 1807 by Humphry Davy, because he isolated it from caustic soda (sodium hydroxide).
A silvery soft waxy metallic element of the alkali metal group; occurs abundantly in natural compounds (especially in salt water); burns with a yellow flame and reacts violently in water; occurs in sea water and in the mineral halite.
Sinonimi: Mg | atomic number 12
ETYM New Lat. and French See Magnesia.
Lightweight, very ductile and malleable, silver-white, metallic element, symbol Mg, atomic number 12, atomic weight 24.305. It is one of the alkaline-earth metals, and the lightest of the commonly used metals. Magnesium silicate, carbonate, and chloride are widely distributed in nature. The metal is used in alloys and flash photography. It is a necessary trace element in the human diet, and green plants cannot grow without it since it is an essential constituent of the photosynthetic pigment chlorophyll (C55H72MgN4O5).
It was named for the ancient Greek city of Magnesia, near where it was first found. It was first recognized as an element by Scottish chemist Joseph Black 1755 and discovered in its oxide by English chemist Humphry Davy 1808. Pure magnesium was isolated 1828 by French chemist Antoine-Alexandre-Brutus Bussy.
A light silver-white ductile bivalent metallic element; in pure form it burns with brilliant white flame; occurs naturally only in combination (as in magnesite, dolomite, carnallite, spinel and olivine); SYN. Mg, atomic number 12.
ETYM Latin alumen. Related to Alum.
The metallic base of alumina. The metal is white, but with a bluish tinge, and is remarkable for its resistance to oxidation, and for its lightness, pertaining a specific gravity of about 2.6. Atomic weight 27.08. Symbol Al.
Light, malleable white metal, resistant to organic salts, obtained by heating aluminum oxide.
Lightweight, silver-white, ductile and malleable, metallic element, symbol Al, atomic number 13, atomic weight 26.9815, melting point 658şC. It is the third most abundant element (and the most abundant metal) in the Earth's crust, of which it makes up about 8.1% by mass. It oxidizes rapidly, the layer of oxide on its surface making it highly resistant to tarnish, and is an excellent conductor of electricity. In its pure state aluminum is a weak metal, but when combined with elements such as copper, silicon, or magnesium it forms alloys of great strength. In nature it is found only in the combined state in many minerals, and is prepared commercially from the ore bauxite.
Aluminum is a reactive element with stable compounds, and the pure metal was not readily obtained until the middle of the 19th century. Because of its light weight (specific gravity 2.70) it is widely used in the shipbuilding and aircraft industries.
Consumer uses include food and beverage packaging, foil, outdoor furniture, and homebuilding materials.
Aluminum was first discovered by Sir Humphry Davy in 1807 and first produced in 1827 by Hans Oersted, who fused potassium with the anhydrous chloride of aluminum in a closed crucible, obtaining the metal in the form of a gray powder. Afterwards Friedrich Wöhler improved this method and succeeded in procuring the metal in a purer form in fused globules and in determining its relative density. In 1854 Henri Sainte-Claire Deville tried the same process, but replaced the potassium by sodium, and the “silver made from clay” of the Paris exhibition of 1855 drew much attention to the question of its economical production. However, no easy way could be found to produce it, and the shiny new metal became more precious than gold. Napoleon is said to have had a set of aluminum cutlery made for his most honored guests. The method now used for its commercial production is the electrolysis of alumina. An iron pot, lined with carbon, is charged with cryolite and heated to about 800şC by the electric current. For the electro
Lysis, a bundle of carbon rods is used as the anode, while the pot itself forms the cathode. The oxygen liberated combines with the carbon of the anode to form carbon dioxide, while the aluminum falls to the bottom of the vessel. More alumina is added and the process continued, the molten metal being drawn off from time to time.
Aluminum is used in the Thermit process for the extraction of high-melting metals from their oxides. Aluminum oxide (see alumina) is used in the manufacture of refractory bricks and as an adsorption filter in chromatography. Aluminum hydroxide is used as a mordant in dyeing and aluminum chloride as a catalyst in organic reactions. Aluminum sulfate is the most widely used chemical in water treatment worldwide, but accidental excess makes drinking water highly toxic, and discharge into rivers kills all fish.A silvery ductile metallic element found primarily in bauxite; SYN. aluminium, Al, atomic number 13.
Sinonimi: Si | atomic number 14
A tetravalent nonmetallic element; next to oxygen it is the most abundant element in the earth's crust; occurs in clay, feldspar, granite, quartz and sand; used as a semiconductor in transistors; SYN. Si, atomic number 14.
A semiconductor used in many devices, especially microchips. Silicon, with atomic number 14 and atomic weight 28, is the second most common element in nature. Compare silicone.
Brittle, nonmetallic element, symbol Si, atomic number 14, atomic weight 28.086. It is the second-most abundant element (after oxygen) in the Earth’s crust and occurs in amorphous and crystalline forms. In nature it is found only in combination with other elements, chiefly with oxygen in silica (silicon dioxide, SiO2) and the silicates. These form the mineral quartz, which makes up most sands, gravels, and beaches.
Pottery glazes and glassmaking are based on the use of silica sands and date from prehistory. Today the crystalline form of silicon is used as a deoxidizing and hardening agent in steel, and has become the basis of the electronics industry because of its semiconductor properties, being used to make “silicon chips” for microprocessors.
The element was isolated by Swedish chemist Jöns Berzelius in 1823, having been named in 1817 by Scottish chemist Thomas Thomson by analogy with boron and carbon because of its chemical resemblance to these elements.
Sinonimi: atomic number 15
ETYM Latin, the morning star, Greek, light bringer; phos light + pherein to bring.
Highly reactive, nonmetallic element, symbol P, atomic number 15, atomic weight 30.9738. It occurs in nature as phosphates (commonly in the form of the mineral apatite), and is essential to plant and animal life. Compounds of phosphorus are used in fertilizers, various organic chemicals, for matches and fireworks, and in glass and steel.
Phosphorus was first identified 1674 by German alchemist Hennig Brand (c. 1630–?), who prepared it from urine. The element has three allotropic forms: a black powder; a white-yellow, waxy solid that ignites spontaneously in air to form the poisonous gas phosphorus pentoxide; and a red-brown powder that neither ignites spontaneously nor is poisonous.
A multivalent nonmetallic element of the nitrogen family that occurs commonly in inorganic phosphate rocks and as organic phosphates in living cells; is highly reactive and occurs in several allotropic forms; SYN. atomic number 15.
Sinonimi: Cl | atomic number 17
ETYM Greek, pale green, greenish yellow. So named from its color.
A common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent; occurs naturally as a salt (as in sea water); SYN. Cl, atomic number 17.
Greenish-yellow, gaseous, nonmetallic element with a pungent odor, symbol Cl, atomic number 17, atomic weight 35.453. It is a member of the halogen group and is widely distributed, in combination with the alkali metals, as chlorates or chlorides.
In nature it is always found in the combined form, as in hydrochloric acid, produced in the mammalian stomach for digestion. Chlorine is obtained commercially by the electrolysis of concentrated brine and is an important bleaching agent and germicide, used for both drinking and swimming-pool water. As an oxidizing agent it finds many applications in organic chemistry. The pure gas (Cl2) is a poison and was used in gas warfare in World War I, where its release seared the membranes of the nose, throat, and lungs, producing pneumonia. Chlorine is a component of chlorofluorocarbons (CFCs) and is partially responsible for the depletion of the ozone layer; it is released from the CFC molecule by the action of ultraviolet radiation in the upper atmosphere, making it available to react with and destroy the ozone. Chlorine was discovered 1774 by the German chemist Karl Scheele, but English chemist Humphry Davy first proved it to be an element 1810 and named it after its color.
Some typical reactions are given below.
When dry chlorine is passed over a heated metal, the chloride is formed.
Zn + Cl2 ® ZnCl2 2Fe + 3Cl2 ® 2FeCl3.
The same reaction occurs with certain nonmetals, when the dry gas is passed over the heated element.
2P + 5Cl2 ® 2PCl5.
With water, chlorine forms a bleaching solution.
H2O + Cl2 ® HCl + HOCl 2OCl- ® 2Cl- + O2.
Iron (II) salts are oxidized to iron (III) salts.
2FeCl2 + Cl2 ® 2FeCl3.
Organic compounds undergo halogenation.
C2H6 + Cl2 ® C2H5Cl + HCl C2H4 + Cl2 ® C2H4Cl2.
Alkalis form chlorides, chlorates, and water.
2NaOH + Cl2 ® NaCl + NaOCl + H2O.
Other halogens are displaced in a redox reaction.
2KBr + Cl2 ® 2KCl + Br2.
Sinonimi: Ar | atomic number 18
Inert gas contained in very small quantity in atmosphere, used to fill electric light bulbs.
Colorless, odorless, nonmetallic, gaseous element, symbol Ar, atomic number 18, atomic weight 39.948. It is grouped with the inert gases, since it was long believed not to react with other substances, but observations now indicate that it can be made to combine with boron fluoride to form compounds. It constitutes almost 1% of the Earth's atmosphere, and was discovered 1894 by British chemists John Rayleigh (1842–1919) and William Ramsay after all oxygen and nitrogen had been removed chemically from a sample of air. It is used in electric discharge tubes and argon lasers.A colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere; SYN. Ar, atomic number 18.
ETYM New Lat. Related to Potassa, Potash.
A light soft silver-white metallic element of the alkali metal group; oxidizes rapidly in air and reacts violently with water; is abundant in nature in combined forms occurring in sea water and in carnallite and kainite and sylvite.
Soft, waxlike, silver-white, metallic element, symbol K (Latin kalium), atomic number 19, atomic weight 39.0983. It is one of the alkali metals and has a very low density—it floats on water, and is the second lightest metal (after lithium). It oxidizes rapidly when exposed to air and reacts violently with water. Of great abundance in the Earth’s crust, it is widely distributed with other elements and found in salt and mineral deposits in the form of potassium aluminum silicates.
Potassium is the main base ion of the fluid in the body's cells. Along with sodium, it is important to the electrical potential of the nervous system and, therefore, for the efficient functioning of nerve and muscle. Shortage, which may occur with excessive fluid loss (prolonged diarrhea, vomiting), may lead to muscular paralysis; potassium overload may result in cardiac arrest. It is also required by plants for growth. The element was discovered and named in 1807 by English chemist Humphry Davy, who isolated it from potash in the first instance of a metal being isolated by electric current.
Sinonimi: Ca | atomic number 20
ETYM New Lat., from Latin calx, calcis, lime; cf French calcium. Related to Calx.
Soft, silvery-white metallic element, symbol Ca, atomic number 20, atomic weight 40.08. It is one of the alkaline-earth metals. It is the fifth most abundant element (the third most abundant metal) in the Earth’s crust. It is found mainly as its carbonate CaCO3, which occurs in a fairly pure condition as chalk and limestone (see calcite). Calcium is an essential component of bones, teeth, shells, milk, and leaves, and it forms 1.5% of the human body by mass.
Calcium ions in animal cells are involved in regulating muscle contraction, blood clotting, hormone secretion, digestion, and glycogen metabolism in the liver. It is acquired mainly from milk and cheese, and its uptake is facilitated by vitamin D. Calcium deficiency leads to spasming of the muscles (tetany); an excess of calcium may lead to the formation of stones (see calculus) in the kidney or gall bladder.
The element was discovered and named by the English chemist Humphry Davy in 1808. Its compounds include slaked lime (calcium hydroxide, Ca(OH)2); plaster of Paris (calcium sulfate, CaSO4.2H2O); calcium phosphate (Ca3(PO4)2), the main constituent of animal bones; calcium hypochlorite (CaOC12), a bleaching agent; calcium nitrate (Ca(NO3)2.4H2O), a nitrogenous fertilizer; calcium carbide (CaC2), which reacts with water to give ethyne (acetylene); calcium cyanamide (CaCN2), the basis of many pharmaceuticals, fertilizers, and plastics, including melamine; calcium cyanide (Ca(CN)2), used in the extraction of gold and silver and in electroplating; and others used in baking powders and fillers for paints.
A white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals; SYN. Ca, atomic number 20.
Sinonimi: Sc | atomic number 21
ETYM New Lat. So called because found in Scandinavian minerals.
Silver-white, metallic element of the lanthanide series, symbol Sc, atomic number 21, atomic weight 44.956.
Its compounds are found widely distributed in nature, but only in minute amounts. The metal has little industrial importance.
Scandium is relatively more abundant in the Sun and other stars than on Earth. Scandium oxide (scandia) is used as a catalyst, in making crucibles and other ceramic parts, and scandium sulfate (in very dilute aqueous solution) is used in agriculture to improve seed germination.
The element was discovered and named in 1879 by Swedish chemist Lars Nilson (1840–99), for Latin Scandia, because it occurs in the Scandinavian mineral euxenite, on which he worked.
A white trivalent metallic element; sometimes classified in the rare earth group; occurs in the Scandinavian mineral thortveitite; SYN. Sc, atomic number 21.
Sinonimi: Ti | atomic number 22
ETYM New Lat., from Latin Titani or Titanes, Greek, the sons of the earth.
Strong, lightweight, silver-gray, metallic element, symbol Ti, atomic number 22, atomic weight 47.90. The ninth-most abundant element in the Earth's crust, its compounds occur in practically all igneous rocks and their sedimentary deposits. It is very strong and resistant to corrosion, so it is used in building high-speed aircraft and spacecraft; it is also widely used in making alloys, as it unites with almost every metal except copper and aluminum. Titanium oxide is used in high-grade white pigments.
Titanium bonds with bone in a process called osseointegration. As the body does not react to the titanium it is valuable for permanent implants such as prostheses.
The element was discovered 1791 by English mineralogist William Gregor (1761–1817) and was named by German chemist Martin Klaproth 1796 after the titans, the giants of Greek mythology. It was not obtained in pure form until 1925.
A light strong gray lustrous corrosion-resistant metallic element used in strong light-weight alloys (as for airplane parts); the main sources are rutile and ilmenite; SYN. Ti, atomic number 22.
Sinonimi: V | atomic number 23
ETYM New Lat., from Icel. Vanadîs, a surname of the Scandinavian goddess Freya.
Silver-white, malleable and ductile, metallic element, symbol V, atomic number 23, atomic weight 50.942. It occurs in certain iron, lead, and uranium ores and is widely distributed in small quantities in igneous and sedimentary rocks. It is used to make steel alloys, to which it adds tensile strength.
Spanish mineralogist Andrés del Rio (1764–1849) and Swedish chemist Nils Sefström (1787–1845) discovered vanadium independently, the former 1801 and the latter 1831. Del Rio named it “erythronium”, but was persuaded by other chemists that he had not in fact discovered a new element; Sefström gave it its present name, after the Norse goddess of love and beauty, Vanadis (or Freya).
A soft silvery white toxic metallic element used in steel alloys; it occurs in several complex minerals including carnotite and vanadinite; SYN. V, atomic number 23.
Another word for chromium when it is used in dyes or pigments.
Sinonimi: Cr | atomic number 24
ETYM New Lat., from Greek khroma color.
Hard, brittle, gray-white, metallic element, symbol Cr, atomic number 24, atomic weight 51.996. It takes a high polish, has a high melting point, and is very resistant to corrosion. It is used in chromium electroplating, in the manufacture of stainless steel and other alloys, and as a catalyst. Its compounds are used for tanning leather and for alums. In human nutrition it is a vital trace element. In nature, it occurs chiefly as chrome iron ore or chromite (FeCr2O4). Kazakhstan, Zimbabwe, and Brazil are sources.
The element was named 1797 by the French chemist Louis Vauquelin (1763–1829) after its brightly colored compounds.
A hard brittle blue-white multivalent metallic element; resistant to corrosion and tarnishing; SYN. Cr, atomic number 24.
Sinonimi: Mn | atomic number 25
ETYM French mangančse, Italian manganese, sasso magnesio; prob. corrupted from Latin magnes, because of its resemblance to the magnet. Related to Magnet, Magnesia.
A hard brittle gray polyvalent metallic element that resembles iron but is not magnetic; used in making steel; occurs in many minerals; SYN. Mn, atomic number 25.
Hard, brittle, gray-white metallic element, symbol Mn, atomic number 25, atomic weight 54.9380. It resembles iron (and rusts), but it is not magnetic and is softer. It is used chiefly in making steel alloys, also alloys with aluminum and copper.
It is used in fertilizers, paints, and industrial chemicals. It is a necessary trace element in human nutrition. The name is old, deriving from the French and Italian forms of Latin for magnesia (MgO), the white tasteless powder used as an antacid from ancient times.
Latin ferrum, iron.
ETYM Old Eng. iren, AS. îren, îsen, îsern; akin to Dutch ijzer, OS. îsarn, Old High Germ. îsarn, îsan, German eisen, Icel. îsarn, jârn, Swed. and Dan. jern, and perh. to Eng. ice; cf. Irish iarann, W. haiarn, Armor. houarn.
1. A heavy ductile magnetic metallic element; is silver-white in pure form but readily rusts; used in construction and tools and armament; plays a role in the transport of oxygen by the blood; SYN. Fe, atomic number 26.
2. Metal shackles; for hands or legs; SYN. irons, chain, chains.
3. A golfclub that has a relatively narrow metal head.
4. A rod used to brand live stock; SYN. branding iron.
A hard, malleable and ductile, silver-gray metallic element, symbol Fe (from Latin ferrum), atomic number 26, atomic weight 55.847. It is the fourth-most abundant element (the second-most abundant metal after aluminum) in the Earth’s crust. The central core of the Earth, the radius of which is believed to be 2,200 miles, is held to consist principally of iron with some nickel. When the amounts in the crust and core are combined, iron is probably the most abundant constituent element of the planet.
Although it almost always occurs in ores or as compounds, it sometimes occurs as a free metal (native metal), occasionally as fragments of iron or iron-nickel meteorites. Iron is the most common and most useful of all metals; it is strongly magnetic and is noted for becoming oxidized (rusted) in moist air. Iron is an essential component of hemoglobin, the molecule in the red blood cells, where it serves to transport oxygen to all parts of the body. Iron is the basis for steel, an alloy with carbon and other elements. Iron has been worked into tools by early peoples in both the Old World and the New and its use has persisted since the Iron Age of prehistory.
Sinonimi: Co | atomic number 27
ETYM German kobalt, prob. from kobold, kobel, goblin, Mid. High Germ. kobolt.
Hard, lustrous, gray, metallic element, symbol Co, atomic number 27, atomic weight 58.933. It is found in various ores and occasionally as a free metal, sometimes in metallic meteorite fragments. It is used in the preparation of magnetic, wear-resistant, and high-strength alloys; its compounds are used in inks, paints, and varnishes.
The isotope Co-60 is radioactive (half-life 5.3 years) and is produced in large amounts for use as a source of gamma rays in industrial radiography, research, and cancer therapy. Cobalt was named in 1730 by Swedish chemist Georg Brandt (1694–1768); the name derives from the fact that miners considered its ore worthless because of its arsenic content.
A hard ferromagnetic silver-white bivalent or trivalent metallic element; a trace element in plant and animal nutrition; SYN. Co, atomic number 27.
Sinonimi: Ni | atomic number 28
ETYM German, from Swed. nickel, abbrev. from Swed. kopparnickel copper-nickel, a name given in derision, as it was thought to be a base ore of copper. The origin of the second part of the word is uncertain. Related to Kupfer-nickel, Copper-nickel.
Hard, malleable and ductile, silver-white metallic element, symbol Ni, atomic number 28, atomic weight 58.71. It occurs in igneous rocks and as a free metal (native metal), occasionally occurring in fragments of iron-nickel meteorites. It is a component of the Earth's core, which is held to consist principally of iron with some nickel. It has a high melting point, low electrical and thermal conductivity, and can be magnetized. It does not tarnish and therefore is much used for alloys, electroplating, and for coinage.
It was discovered in 1751 by Swedish mineralogist Axel Cronstedt (1722–1765) and the name given as an abbreviated form of kopparnickel, Swedish “false copper”, since the ore in which it is found resembles copper but yields none.1. A us coin worth one twentieth of a dollar.
2. A hard malleable ductile silvery metallic element that is resistant to corrosion; used in alloys; occurs in pentlandite and smaltite and garnierite and millerite; SYN. Ni, atomic number 28.
Sinonimi: Cu | atomic number 29 | copper color
ETYM Old Eng. coper, Late Lat. cuper, from Latin cuprum for earlier Cyprium, Cyprium aes, i.e., Cyprian brass. Related to Cypreous.
Orange-pink, very malleable and ductile, metallic element, symbol Cu (from Latin cuprum), atomic number 29, atomic weight 63.546. It is used for its durability, pliability, high thermal and electrical conductivity, and resistance to corrosion.
It was the first metal used systematically for tools by humans; when mined and worked into utensils it formed the technological basis for the Copper Age in prehistory. When alloyed with tin it forms bronze, which strengthens the copper, allowing it to hold a sharp edge; the systematic production and use of this was the basis for the prehistoric Bronze Age. Brass, another hard copper alloy, includes zinc. The element’s name comes from the Greek for Cyprus (Kyprios), where copper was mined.1. A ductile malleable reddish-brown corrosion-resistant diamagnetic metallic element; occurs in various minerals but is the only metal that occurs abundantly in large masses; SYN. Cu, atomic number 29.
2. A reddish brown the color of polished copper; SYN. copper color.
3. A copper penny.
4. Any of various small butterflies of the family Lycaenidae having copper colored wings.
Sinonimi: Zn | atomic number 30
ETYM German zink, probably akin to zinn tin: cf. French zinc, from the German. Related to Tin.
A bluish-white lustrous metallic element; brittle at ordinary temperatures but malleable when heated; used in a wide variety of alloys and in galvanizing iron; it occurs as zinc sulphide in zinc blende; SYN. Zn, atomic number 30.
Hard, brittle, bluish white, metallic element, symbol Zn, atomic number 30, atomic weight 65.37. The principal ore is sphalerite or zinc blende (zinc sulfide, ZnS). Zinc is little affected by air or moisture at ordinary temperatures; its chief uses are in alloys such as brass and in coating metals (for example, galvanized iron). Its compounds include zinc oxide, used in ointments (as an astringent) and cosmetics, paints, glass, and printing ink.
Zinc has been used as a component of brass since the Bronze Age, but it was not recognized as a separate metal until 1746, when it was described by German chemist Andreas Sigismund Marggraf (1709–1782). The name derives from the shape of the crystals on smelting.
Sinonimi: Ga | atomic number 31
Gray metallic element, symbol Ga, atomic number 31, relative atomic mass 69.75. It is liquid at room temperature. Gallium arsenide (GaAs) crystals are used in microelectronics, since electrons travel a thousand times faster through them than through silicon. The element was discovered in 1875 by Lecoq de Boisbaudran (1838–1912).
A rare silvery (usually trivalent) metallic element; brittle at low temperatures but liquid above room temperature; occurs in trace amounts in bauxite and zinc ores; SYN. Ga, atomic number 31.
Sinonimi: Ge | atomic number 32
ETYM New Lat., from Latin Germania Germany.
A semiconductor element (atomic number 32) that is used in some transistors, diodes, and solar cells but has been replaced by silicon in most applications. Germanium has a lower bias voltage than silicon but is more sensitive to heat (as in soldering).
Brittle, gray-white, weakly metallic (metalloid) element, symbol Ge, atomic number 32, atomic weight 72.6. It belongs to the silicon group, and has chemical and physical properties between those of silicon and tin. Germanium is a semiconductor material and is used in the manufacture of transistors and integrated circuits. The oxide is transparent to infrared radiation, and is used in military applications. It was discovered 1886 by German chemist Clemens Winkler (1838–1904).
In parts of Asia, germanium and plants containing it are used to treat a variety of diseases, and it is sold in the West as a food supplement despite fears that it may cause kidney damage.
A brittle gray crystalline element that is a semiconducting metalloid (resembling silicon) used in transistors; occurs in germanite and argyrodite; SYN. Ge, atomic number 32.
ETYM Latin arsenicum, Greek arsenikon, arrenikon, yellow orpiment, perh. from arsenikos or better Attic arrenikos masculine, arrhn male, on account of its strength, or from Per. zernîkh: cf. French arsenic.
Brittle, grayish-white, semimetallic element (a metalloid), symbol As, atomic number 33, atomic weight 74.92. It occurs in many ores and occasionally in its elemental state, and is widely distributed, being present in minute quantities in the soil, the sea, and the human body. In larger quantities, it is poisonous. The chief source of arsenic compounds is as a by-product from metallurgical processes. It is used in making semiconductors, alloys, and solders.
As it is a cumulative poison, its presence in food and drugs is very dangerous. The symptoms of arsenic poisoning are vomiting, diarrhea, tingling and possibly numbness in the limbs, and collapse. It featured in some drugs, including salvarsan, the first specific treatment for syphilis. Its name derives from the Latin arsenicum.
1. A very poisonous metallic element that has three allotropic forms; arsenic and arsenic compounds are used as herbicides and insecticides and various alloys; found in arsenopyrite and orpiment and realgar; SYN. As, atomic number 33.
2. A white powdered poisonous trioxide of arsenic; used in manufacturing glass and as a pesticide and weed killer; SYN. arsenic trioxide, arsenous anhydride, arsenous oxide.
ETYM New Lat., from Greek selene the moon. So called because of its chemical analogy to tellurium (from Latin tellus the earth), being, as it were, a companion to it.
A toxic nonmetallic element related to sulfur and tellurium; occurs in several allotropic forms; a stable gray metallike allotrope conducts electricity better in the light than in the dark and is used in photocells.
Gray, nonmetallic element, symbol Se, atomic number 34, relative atomic mass 78.96. It belongs to the sulfur group and occurs in several allotropic forms that differ in their physical and chemical properties. It is an essential trace element in human nutrition.
Obtained from many sulfide ores and selenides, it is used as a red coloring for glass and enamel.
Because its electrical conductivity varies with the intensity of light, selenium is used extensively in photoelectric devices. It was discovered 1817 by Swedish chemist Jöns Berzelius and named for the Moon because its properties follow those of tellurium, whose name derives from Latin Tellus “Earth”.
Sinonimi: Br | atomic number 35
ETYM Greek, bad smell, stink. Related to Brome.
Non-metallic chlorinelike element found in seawater and mineral springs.
Dark, reddish brown, nonmetallic element, a volatile liquid at room temperature, symbol Br, atomic number 35, relative atomic mass 79.904. It is a member of the halogen group, has an unpleasant odor, and is very irritating to mucous membranes. Its salts are known as bromides.
Bromine was formerly extracted from salt beds but is now mostly obtained from sea water, where it occurs in small quantities. Its compounds are used in photography and in the chemical and pharmaceutical industries.
A nonmetallic largely pentavalent heavy volatile corrosive dark brown liquid element belonging to the halogens; found in sea water; SYN. Br, atomic number 35.
ETYM New Lat., from Greek kryptos hidden.
A colorless element that is one of the six inert gasses; occurs in trace amounts in air; SYN. Kr.
Colorless, odorless, gaseous, nonmetallic element, symbol Kr, atomic number 36, atomic weight 83.80. It is grouped with the inert gases and was long believed not to enter into reactions, but it is now known to combine with fluorine under certain conditions; it remains inert to all other reagents. It is present in very small quantities in the air (about 114 parts per million). It is used chiefly in fluorescent lamps, lasers, and gas-filled electronic valves.
Krypton was discovered 1898 in the residue from liquid air by British chemists William Ramsay and Morris Travers; the name refers to their difficulty in isolating it.
Colorless and odorless rare gas which occurs in the atmosphere.
Sinonimi: Rb | atomic number 37
ETYM New Lat., from Latin rubidus red, from rubere to be red. So called from two dark red spectroscopic lines by means of which it was discovered in the lepidolite from Rozena, Moravia. Related to Rubicund.
Soft, silver-white, metallic element, symbol Rb, atomic number 37, atomic weight 85.47. It is one of the alkali metals, ignites spontaneously in air, and reacts violently with water. It is used in photocells and vacuum-tube filaments.
Rubidium was discovered spectroscopically by German physicists Robert Bunsen and Gustav Kirchhoff in 1861, and named for the red lines in its spectrum.
A soft silvery metallic element of the alkali metal group; burns in air and reacts violently in water; occurs in carnallite and lepidolite and pollucite; SYN. Rb, atomic number 37.
Sinonimi: Sr | atomic number 38
ETYM New Lat. Related to Strontia.
Soft, ductile, pale-yellow, metallic element, symbol Sr, atomic number 38, atomic weight 87.62. It is one of the alkaline-earth metals, widely distributed in small quantities only as a sulfate or carbonate. Strontium salts burn with a red flame and are used in fireworks and signal flares.
The radioactive isotopes Sr-89 and Sr-90 (half-life 25 years) are some of the most dangerous products of the nuclear industry; they are fission products in nuclear explosions and in the reactors of nuclear power plants. Strontium is chemically similar to calcium and deposits in bones and other tissues, where the radioactivity is damaging. The element was named in 1808 by English chemist Humphry Davy, who isolated it by electrolysis, after Strontian, a mining location in Scotland where it was first found.
A soft silver-white or yellowish metallic element of the alkali metal group; turns yellow in air; occurs in celestite and strontianite; SYN. Sr, atomic number 38.
Sinonimi: Y | atomic number 39
ETYM New Lat., from Ytterby, in Sweden. Related to Erbium.
A silvery metallic element that is common in rare-earth minerals; used in magnesium and aluminum alloys; SYN. Y, atomic number 39.
Silver-gray, metallic element, symbol Y, atomic number 39, atomic weight 88.905. It is associated with and resembles the rare earth elements (lanthanides), occurring in gadolinite, xenotime, and other minerals. It is used in color-television tubes and to reduce steel corrosion.
The name derives from the Swedish town of Ytterby, near where it was first discovered 1788. Swedish chemist Carl Mosander (1797–1858) isolated the element 1843.
Sinonimi: Zr | atomic number 40
ETYM New Lat.
A lustrous gray strong metallic element resembling titanium; it is used in nuclear reactors as a neutron absorber; it occurs in baddeleyite but is obtained chiefly from zircon; SYN. Zr, atomic number 40.
Lustrous, grayish-white, strong, ductile, metallic element, symbol Zr, atomic number 40, atomic weight 91.22. It occurs in nature as the mineral zircon (zirconium silicate), from which it is obtained commercially. It is used in some ceramics, alloys for wire and filaments, steel manufacture, and nuclear reactors, where its low neutron absorption is advantageous.
It was isolated 1824 by Swedish chemist Jöns Berzelius. The name was proposed by English chemist Humphry Davy 1808.
Zirconium, a lustrous grey strong metallic element resembling titanium; it is used in nuclear reactors as a neutron absorber; it occurs in baddeleyite but is obtained chiefly from zircon.
Abbreviation for New Brunswick, a Canadian province; nota bene (Latin “note well”), used in references and citations.
Sinonimi: Nb | atomic number 41
ETYM New Lat., from Latin and Eng. Niobe.
A soft gray ductile metallic element used in alloys; occurs in niobite; formerly called columbium; SYN. Nb, atomic number 41.
Soft, gray-white, somewhat ductile and malleable, metallic element, symbol Nb, atomic number 41, atomic weight 92.906. It occurs in nature with tantalum, which it resembles in chemical properties. It is used in making stainless steel and other alloys for jet engines and rockets and for making superconductor magnets.
Niobium was discovered in 1801 by English chemist Charles Hatchett (1765–1847), who named it columbium (symbol Cb), a name that is still used in metallurgy. In 1844 it was renamed after Niobe by German chemist Heinrich Rose (1795–1864) because of its similarity to tantalum (Niobe is the daughter of Tantalus in Greek mythology).
Sinonimi: Mo | atomic number 42
ETYM New Lat.: cf. French molybdčne. Related to Molybdena.
A polyvalent metallic element that resembles chromium and tungsten in its properties; used to strengthen and harden steel; SYN. Mo, atomic number 42.
Ironlike white metal used in steel manufacture and dyeing.
Heavy, hard, lustrous, silver-white, metallic element, symbol Mo, atomic number 42, atomic weight 95.94. The chief ore is the mineral molybdenite. The element is highly resistant to heat and conducts electricity easily. It is used in alloys, often to harden steels. It is a necessary trace element in human nutrition. It was named 1781 by Swedish chemist Karl Scheele, after its isolation by P J Hjelm (1746–1813), for its resemblance to lead ore.
Sinonimi: Tc | atomic number 43
Silver-gray, radioactive, metallic element, symbol Tc, atomic number 43, atomic weight 98.906. It occurs in nature only in extremely minute amounts, produced as a fission product from uranium in pitchblende and other uranium ores. Its longest-lived isotope, Tc-99, has a half-life of 216,000 years. It is a superconductor and is used as a hardener in steel alloys and as a medical tracer.
It was synthesized 1937 (named 1947) by Italian physicists Carlo Perrier and Emilio Segrč, who bombarded molybdenum with deuterons, looking to fill a missing spot in the periodic table of the elements (at that time it was considered not to occur in nature). It was later isolated in large amounts from the fission-product debris of uranium fuel in nuclear reactors.
A crystalline metallic element not found in nature; occurs as one of the fission products of uranium; SYN. Tc, atomic number 43.
Sinonimi: Ru | atomic number 44
ETYM New Lat. So named from the Ruthenians, a Little Russian people, as coming from Russia, the metal having been found in the Ural mountains.
Hard, brittle, silver-white, metallic element, symbol Ru, atomic number 44, atomic weight 101.07. It is one of the so-called platinum group of metals; it occurs in platinum ores as a free metal and in the natural alloy osmiridium. It is used as a hardener in alloys and as a catalyst; its compounds are used as coloring agents in glass and ceramics.
It was discovered by J A Sniadecki in Vilno, Poland 1808, and then rediscovered 1828 by G W Osann and named for its place of discovery, the Ural mountains in Ruthenia (now part of the Ukraine). Pure ruthenium was isolated in 1845 by K K Klaus.
A rare polyvalent metallic element of the platinum group; it is found associated with platinum; SYN. Ru, atomic number 44.
Sinonimi: Rh | atomic number 45
ETYM New Lat., from Greek rodon the rose. So called from the rose-red color of certain of its solutions. Related to Rhododendron.
Hard, silver-white, metallic element, symbol Rh, atomic number 45, atomic weight 102.905. It is one of the so-called platinum group of metals and is resistant to tarnish, corrosion, and acid. It occurs as a free metal in the natural alloy osmiridium and is used in jewelry, electroplating, and thermocouples.
Rhodium was discovered in 1803 by English chemist William Wollaston (1766–1828) and named in 1804 for the red color of its salts in solution.
A white hard metallic element that is one of the platinum group and is found in platinum ores; used in alloys with platinum; SYN. Rh, atomic number 45.
Sinonimi: Pd | atomic number 46
A sliver-white metallic element of the platinum group that resembles platinum; occurs in some copper and nickel ores; does not tarnish at ordinary temperatures and is used (alloyed with gold) in jewelry; SYN. Pd, atomic number 46.
Lightweight, ductile and malleable, silver-white, metallic element, symbol Pd, atomic number 46, atomic weight 106.4.
It is one of the so-called platinum group of metals, and is resistant to tarnish and corrosion. It often occurs in nature as a free metal (see native metal) in a natural alloy with platinum. Palladium is used as a catalyst, in alloys of gold (to make white gold) and silver, in electroplating, and in dentistry.
It was discovered 1803 by British physicist William Wollaston (1766–1828), and named for the then recently discovered asteroid Pallas (found 1802).
ETYM French argent, from Latin argentum, silver; akin to Greek argyros silver, argos, arges, white, bright, Skr. rajata white, silver, raj to shine, Irish arg white, milk, airgiod silver, money, and Latin arguere to make clear. Related to Argue.
A metal tincture used in heraldry to give a silvery appearance.
The heraldic colour silver or white.
Sinonimi: Ag | atomic number 47
ETYM Old Eng. silver, selver, seolver, AS. seolfor, siolfur, siolufr, silofr, sylofr; akin to OS. silubar, OFries. selover, Dutch zilver, LG. sulver, Old High Germ. silabar, silbar, German silber, Icel. silfr, Swed. silfver, Dan. sölv, Goth. silubr, Russ. serebro, Lith. sidabras; of unknown origin.
1. A soft white precious univalent metallic element having the highest electrical and thermal conductivity of any metal; occurs in argentite and in free form; used in coins, jewelry, tableware and photography; SYN. Ag, atomic number 47.
2. Coins made of silver.
White, lustrous, extremely malleable and ductile, metallic element, symbol Ag (from Latin argentum), atomic number 47, atomic weight 107.868. It occurs in nature in ores and as a free metal; the chief ores are sulfides, from which the metal is extracted by smelting with lead. It is one of the best metallic conductors of both heat and electricity; its most useful compounds are the chloride and bromide, which darken on exposure to light and are the basis of photographic emulsions.
Silver is used ornamentally, for jewelry and tableware, for coinage, in electroplating, electrical contacts, and dentistry, and as a solder. It has been mined since prehistory; its name is an ancient non-Indo-European one, silubr, borrowed by the Germanic branch as silber.
Sinonimi: Cd | atomic number 48
ETYM New Lat. Related to Cadmia.
Soft, silver-white, ductile, and malleable metallic element, symbol Cd, atomic number 48, atomic weight 112.40. Cadmium occurs in nature as a sulfide or carbonate in zinc ores. It is a toxic metal that, because of industrial dumping, has become an environmental pollutant. It is used in batteries, electroplating, and as a constituent of alloys used for bearings with low coefficients of friction; it is also a constituent of an alloy with a very low melting point.
Cadmium is also used in the control rods of nuclear reactors, because of its high absorption of neutrons. It was named in 1817 by the German chemist Friedrich Strohmeyer (1776–1835) after Greek mythological character Cadmus.
A soft bluish-white ductile malleable toxic bivalent metallic element; occurs in association with zinc ores; SYN. Cd, atomic number 48.
Abbreviation for compact disc; Corps Diplomatique (French “Diplomatic Corps”); certificate of deposit.
Sinonimi: In | atomic number 49
ETYM New Lat. Related to Indigo.
Soft, ductile, silver-white, metallic element, symbol In, atomic number 49, atomic weight 114.82. It occurs in nature in some zinc ores, is resistant to abrasion, and is used as a coating on metal parts. It was discovered 1863 by German metallurgists Ferdinand Reich (1799–1882) and Hieronymus Richter (1824–1898), who named it after the two indigo lines of its spectrum.
A rare soft silvery metallic element; occurs in small quantities in sphalerite; SYN. In, atomic number 49.
Sinonimi: Sn | atomic number 50
ETYM As. tin; akin to Dutch tin, German zinn, Old High Germ. zin, Icel. and Dan. tin, Swed. tenn; of unknown origin.
Soft, silver-white, malleable and somewhat ductile, metallic element, symbol Sn (from Latin stannum), atomic number 50, atomic weight 118.69. Tin exhibits allotropy, having three forms: the familiar lustrous metallic form above 55.8şF/13.2şC; a brittle form above 321.8şF/161şC; and a gray powder form below 55.8şF/13.2şC (commonly called tin pest or tin disease). The metal is quite soft (slightly harder than lead) and can be rolled, pressed, or hammered into extremely thin sheets; it has a low melting point. In nature it occurs rarely as a free metal. It resists corrosion and is therefore used for coating and plating other metals.
Tin and copper smelted together form the oldest desired alloy, bronze; since the Bronze Age (3500 bc) that alloy has been the basis of both useful and decorative materials. The mines of Cornwall were the principal western source from then until the 19th century, when rich deposits were found in South America, Africa, and se Asia. Tin is also alloyed with metals other than copper to make solder and pewter. It was recognized as an element by Antoine Lavoisier, but the name is very old and comes from the Germanic form zinn.
A silvery malleable metallic element that resists corrosion; used in many alloys and to coat other metals to prevent corrosion; obtained chiefly from cassiterite where it occurs as tin oxide; SYN. Sn, atomic number 50.
Sinonimi: Sb | atomic number 51
ETYM Late Lat. antimonium, of unknown origin.
A metallic element having four allotropic forms; used in a wide variety of alloys; found in stibnite; SYN. Sb, atomic number 51.
Brittle, bluish-white metallic element.
A brittle, crystalline, whitish mineral; metal obtained from antimony and used in alloys and medicine.
Silver-white, brittle, semimetallic element (a metalloid), symbol Sb (from Latin stibium), atomic number 51, atomic weight 121.75. It occurs chiefly as the ore stibnite, and is used to make alloys harder; it is also used in photosensitive substances in color photography, optical electronics, fireproofing, pigment, and medicine. It was employed by the ancient Egyptians in a mixture to protect the eyes from flies.
Sinonimi: Te | atomic number 52
ETYM New Lat., from Latin tellus, -uris, the earth.
Silver-white, semimetallic (metalloid) element, symbol Te, atomic number 52, atomic weight 127.60. Chemically it is similar to sulfur and selenium, and it is considered one of the sulfur group. It occurs naturally in telluride minerals, and is used in coloring glass blue-brown, in the electrolytic refining of zinc, in electronics, and as a catalyst in refining petroleum.
It was discovered by Austrian mineralogist Franz Müller (1740–1825) 1782, and named 1798 by German chemist Martin Klaproth.
A brittle silver-white metalloid element that is related to selenium and sulfur; it is used in alloys and as a semiconductor; occurs mainly as tellurides in ores of copper and nickel and silver and gold; SYN. Te, atomic number 52.
Sinonimi: iodin | I | atomic number 53
ETYM Greek iodes violetlike; ion a violet + eidos form: cf. French iode, iodine. The name was given from the violet color of its vapor. Related to Violet, Idyl.
A nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks); SYN. iodin, I, atomic number 53.
Grayish-black nonmetallic element, symbol I, atomic number 53, atomic weight 126.9044. It is a member of the halogen group. Its crystals give off, when heated, a violet vapor with an irritating odor resembling that of chlorine. It only occurs in combination with other elements. Its salts are known as iodides, which are found in sea water. As a mineral nutrient it is vital to the proper functioning of the thyroid gland, where it occurs in trace amounts as part of the hormone thyroxine. Absence of iodine from the diet leads to goiter. Iodine is used in photography, in medicine as an antiseptic, and in making dyes.
Its radioactive isotope 131I (half-life of eight days) is a dangerous fission product from nuclear explosions and from the nuclear reactors in power plants, since, if ingested, it can be taken up by the thyroid and damage it. It was discovered 1811 by French chemist B Courtois (1777–1838).
Xenon, a colourless odourless inert gaseous element occurring in the earth's atmosphere in trace amounts
Sinonimi: Xe | atomic number 54
ETYM Greek xenos stranger.
A colorless odorless inert gaseous element occurring in the earth's atmosphere in trace amounts; SYN. Xe, atomic number 54.
Colorless, odorless, gaseous, non-metallic element, symbol Xe, atomic number 54, atomic weight 131.30. It is grouped with the inert gases and was long believed not to enter into reactions, but is now known to form some compounds, mostly with fluorine. It is a heavy gas present in very small quantities in the air (about one part in 20 million).
Xenon is used in bubble chambers, light bulbs, vacuum tubes, and lasers. It was discovered in 1898 in a residue from liquid air by Scottish chemists William Ramsay and Morris Travers.
Soft, silvery-white, ductile, metallic element, symbol Cs, atomic number 55, atomic weight 132.905. It is one of the alkali metals, and is the most electropositive of all the elements. In air it ignites spontaneously, and it reacts vigorously with water. It is used in the manufacture of photocells.
The rate of vibration of cesium atoms is used as the standard of measuring time. Its radioactive isotope Cs-137 (half-life 30.17 years) is one of the most dangerous waste products of the nuclear industry; it is a highly radioactive biological analog for potassium, produced as a fission product of nuclear explosions and in the reactors of nuclear power plants. It was named in 1860 by Robert Bunsen, German chemist, from the blueness of its spectral line.
A soft silver-white ductile metallic element (liquid at normal temperatures); the most electropositive and alkaline metal; SYN. caesium, Cs, atomic number 55.
Sinonimi: Ba | atomic number 56
ETYM New Lat., from Greek barys heavy.
White metallic element. barium meal, drink containing a compound of barium which is opaque to X-rays, taken before or during X-ray examination of digestive tract.
Soft, silver-white, metallic element, symbol Ba, atomic number 56, atomic weight 137.33. It is one of the alkaline-earth metals, found in nature as barium carbonate and barium sulfate. As the sulfate it is used in medicine: taken as a suspension (a “barium meal”), its movement along the gut is followed using X-rays. The barium sulfate, which is opaque to X-rays, shows the shape of the gut, revealing any abnormalities of the alimentary canal. Barium is also used in alloys, pigments, and safety matches and, with strontium, forms the emissive surface in cathode-ray tubes. It was first discovered in barytes or heavy spar.
A soft silvery metallic element of the alkali earth group; found in barite; SYN. Ba, atomic number 56.
Sinonimi: La | atomic number 57
ETYM New Lat., from Greek lanthanein to lie hid, to be concealed.
Soft, silvery, ductile and malleable, metallic element, symbol La, atomic number 57, atomic weight 138.91, the first of the lanthanide series. It is used in making alloys. It was named 1839 by Swedish chemist Carl Mosander (1797–1858).
A white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth; SYN. La, atomic number 57.
Sinonimi: Pr | atomic number 59
Silver-white, malleable, metallic element of the lanthanide series, symbol Pr, atomic number 59, atomic weight 140.907. It occurs in nature in the minerals monzanite and bastnaesite, and its green salts are used to color glass and ceramics. It was named in 1885 by Austrian chemist Carl von Welsbach (1858–1929).
He fractionated it from dydymium (originally thought to be an element but actually a mixture of rare-earth metals consisting largely of neodymium, praseodymium, and cerium), and named it for its green salts and spectroscopic line.
A soft yellowish-white trivalent metallic element of the rare earth group; can be recovered from bastnasite or monazite by an ion-exchange process; SYN. Pr, atomic number 59.
Abbreviation for the state of North Dakota.
Sinonimi: Nd | atomic number 60
Yellowish metallic element of the lanthanide series, symbol Nd, atomic number 60, atomic weight 144.24. Its rose-colored salts are used in coloring glass, and neodymium is used in lasers.
It was named in 1885 by Austrian chemist Carl von Welsbach (1858–1929), who fractionated it away from didymium (originally thought to be an element but actually a mixture of rare-earth metals consisting largely of neodymium, presodymium, and cerium).
A yellow trivalent metallic element of the rare earth group; occurs in monazite and bastnasite in association with cerium and lanthanum and praseodymium; SYN. Nd, atomic number 60.
Sinonimi: Pm | atomic number 61
Radioactive, metallic element of the lanthanide series, symbol Pm, atomic number 61, atomic weight 145.
It occurs in nature only in minute amounts, produced as a fission product/by-product of uranium in pitchblende and other uranium ores; for a long time it was considered not to occur in nature. The longest-lived isotope has a half-life of slightly more than 20 years.
Promethium is synthesized by neutron bombardment of neodymium, and is a product of the fission of uranium, thorium, or plutonium; it can be isolated in large amounts from the fission-product debris of uranium fuel in nuclear reactors. It is used in phosphorescent paints and as an X-ray source.
It was named in 1949 after the Greek Titan Prometheus by G M Coryell for the element isolated by US physicists J A Marinsky and L E Glendenin.A soft silvery metallic element of the rare earth group having no stable isotope; was discovered in radioactive form as a fission product of uranium; SYN. Pm, atomic number 61.
Sinonimi: Sm | atomic number 62
ETYM New Lat., from Eng. samarskite.
Hard, brittle, gray-white, metallic element of the lanthanide series, symbol Sm, atomic number 62, atomic weight 150.4. It is widely distributed in nature and is obtained commercially from the minerals monzanite and bastnaesite. It is used only occasionally in industry, mainly as a catalyst in organic reactions. Samarium was discovered by spectroscopic analysis of the mineral samarskite and named in 1879 by French chemist Paul Lecoq de Boisbaudran (1838–1912) after its source.
A gray lustrous metallic element of the rare earth group; is used in special alloys; occurs in monazite and bastnasite; SYN. Sm, atomic number 62.
Sinonimi: Eu | atomic number 63
ETYM New Lat.; Europe + -ium, as in aluminium.
A bivalent and trivalent metallic element of the rare earth group; SYN. Eu, atomic number 63.
Soft, grayish, metallic element of the lanthanide series, symbol Eu, atomic number 63, atomic weight 151.96. It is used in lasers and as the red phosphor in color televisions; its compounds are used to make control rods for nuclear reactors. It was named in 1901 by French chemist Eugčne Demarçay (1852–1904) after the continent of Europe, where it was first found.
Sinonimi: Gd | atomic number 64
ETYM New Lat. Related to Gadolinite.
Silvery-white metallic element of the lanthanide series, symbol Gd, atomic number 64, atomic weight 157.25. It is found in the products of nuclear fission and used in electronic components, alloys, and products needing to withstand high temperatures.
A ductile silvery-white ductile ferromagnetic trivalent metallic element of the rare earth group; SYN. Gd, atomic number 64.
Sinonimi: Tb | atomic number 65
ETYM New Lat., from Ytterby, in Sweden. Related to Erbium.
Soft, silver-gray, metallic element of the lanthanide series, symbol Tb, atomic number 81, atomic weight 158.925. It occurs in gadolinite and other ores, with yttrium and ytterbium, and is used in lasers, semiconductors, and television tubes. It was named in 1843 by Swedish chemist Carl Mosander (1797–1858) for the town of Ytterby, Sweden, where it was first found.
A metallic element of the rare earth group; used in lasers; occurs in apatite and monazite and xenotime and ytterbite; SYN. Tb, atomic number 65.
Sinonimi: Dy | atomic number 66
ETYM New Lat., from Greek dysprositos hard to get at.
Silver-white, metallic element of the lanthanide series, symbol Dy, atomic number 66, atomic weight 162.50. It is among the most magnetic of all known substances and has a great capacity to absorb neutrons.
It was discovered 1886 by French chemist Paul Lecoq de Boisbaudran (1838–1912).
A trivalent metallic element of the rare earth group; forms compounds that are highly magnetic; SYN. Dy, atomic number 66.
Sinonimi: Ho | atomic number 67
ETYM New Lat., of uncertain origin.
Silvery, metallic element of the lanthanide series, symbol Ho, atomic number 67, atomic weight 164.93. It occurs in combination with other rare-earth metals and in various minerals such as gadolinite. Its compounds are highly magnetic.
The element was discovered in 1878, spectroscopically, by the Swiss chemists L Soret and Delafontaine, and independently in 1879 by Swedish chemist Per Cleve (1840–1905), who named it after Stockholm, near which it was found.
A trivalent metallic element of the rare earth group; occurs together with yttrium; forms highly magnetic compounds; SYN. Ho, atomic number 67.
Sinonimi: Er | atomic number 68
Soft, lustrous, grayish, metallic element of the lanthanide series, symbol Er, atomic number 68, atomic weight 167.26. It occurs with the element yttrium or as a minute part of various minerals. It was discovered 1843 by Carl Mosander (1797–1858), and named for the town of Ytterby, Sweden, near which the lanthanides (rare-earth elements) were first found.A trivalent metallic element of the rare earth group; occurs with yttrium; SYN. Er, atomic number 68.
Sinonimi: Tm | atomic number 69
ETYM New Lat. Related to Thule.
Soft, silver-white, malleable and ductile, metallic element, of the lanthanide series, symbol Tm, atomic number 69, atomic weight 168.94. It is the least abundant of the rare-earth metals, and was first found in gadolinite and various other minerals. It is used in arc lighting.
The X-ray-emitting isotope Tm-170 is used in portable X-ray units. Thulium was named by French chemist Paul Lecoq de Boisbaudran 1886 after the northland, Thule.
A soft silvery metallic element of the rare earth group; isotope 170 emits X-rays and is used in small portable X-ray machines; it occurs in monazite and apatite and xenotime; SYN. Tm, atomic number 69.
Sinonimi: Yb | atomic number 70
ETYM New Lat., from Ytterby, in Sweden. Related to Erbium.
A soft silvery metallic element; a rare earth of the lanthanide series; it occurs in gadolinite and monazite and xenotime; SYN. Yb, atomic number 70.
Soft, lustrous, silvery, malleable, and ductile element of the lanthanide series, symbol Yb, atomic number 70, atomic weight 173.04. It occurs with (and resembles) yttrium in gadolinite and other minerals, and is used in making steel and other alloys.
In 1878 Swiss chemist Jean-Charles de Marignac gave the name ytterbium (after the Swedish town of Ytterby, near where it was found) to what he believed to be a new element. French chemist Georges Urbain (1872–1938) discovered 1907 that this was in fact a mixture of two elements: ytterbium and lutetium.
Sinonimi: lutecium | Lu | atomic number 71
Silver-white, metallic element, the last of the lanthanide series, symbol Lu, atomic number 71, atomic weight 174.97. It is used in the “cracking”, or breakdown, of petroleum and in other chemical processes. It was named by its discoverer, French chemist Georges Urbain, (1872–1938) after his native city.
A trivalent metallic element of the rare earth group; usually occurs in association with yttrium; SYN. lutecium, Lu, atomic number 71.
Sinonimi: Hf | atomic number 72
A gray tetravalent metallic element that resembles zirconium chemically and is found in zirconium minerals; used in filaments for its ready emission of electrons; SYN. Hf, atomic number 72.
Silvery, metallic element, symbol Hf, atomic number 72, relative atomic mass 178.49. It occurs in nature in ores of zirconium, the properties of which it resembles. Hafnium absorbs neutrons better than most metals, so it is used in the control rods of nuclear reactors; it is also used for light-bulb filaments.
It was named in 1923 by Dutch physicist Dirk Coster (1889–1950) and Hungarian chemist Georg von Hevesy after the city of Copenhagen, where the element was discovered.
Symbol for hafnium.
Sinonimi: Ta | atomic number 73
ETYM New Lat. So named on account of the perplexity and difficulty encounterd by its discoverer (Ekeberg) in isolating it. Related to Tantalus.
Hard, ductile, lustrous, gray-white, metallic element, symbol Ta, atomic number 73, atomic weight 180.948. It occurs with niobium in tantalite and other minerals. It can be drawn into wire with a very high melting point and great tenacity, useful for lamp filaments subject to vibration. It is also used in alloys, for corrosion-resistant laboratory apparatus and chemical equipment, as a catalyst in manufacturing synthetic rubber, in tools and instruments, and in rectifiers and capacitors.
It was discovered and named 1802 by Swedish chemist Anders Ekeberg (1767–1813) after the mythological Greek character Tantalus.
A hard gray lustrous metallic element that is highly corrosion-resistant; occurs in niobite and fergusonite and tantalite; SYN. Ta, atomic number 73.
ETYM Swed. tungsten (cf. Dan. tungsteen, German tungstein); tung heavy (akin to Dan. tung, Icel. thungr) + sten stone. Related to Stone.
A heavy gray-white metallic element; the pure form is used mainly in electrical applications; it is found in several ores including wolframite and scheelite; SYN. wolfram, W, atomic number 74.
Hard, heavy, gray-white, metallic element, symbol W (from German Wolfram), atomic number 74, atomic weight 183.85. It occurs in the minerals wolframite, scheelite, and hubertite. It has the highest melting point of any metal (6,170şF/3,410şC) and is added to steel to make it harder, stronger, and more elastic; its other uses include high-speed cutting tools, electrical elements, and thermionic couplings. Its salts are used in the paint and tanning industries.
Tungsten was first recognized in 1781 by Swedish chemist Karl Scheele in the ore scheelite. It was isolated in 1783 by Spanish chemists Fausto D'Elhuyar (1755–1833) and his brother Juan José (1754–1796).
White metal, also called wolfram, with highest melting point of all metals, used in filaments of electric lamps, steel alloys, etc.
Alternate name for tungsten
Sinonimi: Re | atomic number 75
Heavy, silver-white, metallic element, symbol Re, atomic number 75, atomic weight 186.2. It has chemical properties similar to those of manganese and a very high melting point (3,180şC/5,756şF), which makes it valuable as an ingredient in alloys.
It was identified and named in 1925 by German chemists W Noddack (1893–1960), I Tacke, and O Berg from the Latin name for the river Rhine.
A rare heavy polyvalent metallic element that resembles manganese chemically and is used in some alloys; is obtained as a by-product in refining molybdenum; SYN. Re, atomic number 75.
Sinonimi: Os | atomic number 76
ETYM Greek osme a smell, odor.
Hard, heavy, bluish white, metallic element, symbol Os, atomic number 76, atomic weight 190.2. It is the densest of the elements, and is resistant to tarnish and corrosion. It occurs in platinum ores and as a free metal (see native metal) with iridium in a natural alloy called osmiridium, containing traces of platinum, ruthenium, and rhodium. Its uses include pen points and light-bulb filaments; like platinum, it is a useful catalyst.
It was discovered in 1803 and named in 1804 by English chemist Smithson Tennant (1761–1815) after the irritating smell of one of its oxides.
A hard brittle blue-gray or blue-black metallic element that is one of the platinum metals; the heaviest metal known; SYN. Os, atomic number 76.
Sinonimi: Ir | atomic number 77
ETYM New Lat., from Latin iris, iridis, the rainbow. So called from the iridescence of some of its solutions. Related to Iris.
Rare, hard, platinumlike metal.
A heavy brittle metallic element of the platinum group; used in alloys; occurs in natural alloys with platinum or osmium; SYN. Ir, atomic number 77.
Hard, brittle, silver-white, metallic element, symbol Ir, atomic number 77, atomic weight 192.2. It is twice as heavy as lead and is resistant to tarnish and corrosion. It is one of the so-called platinum group of metals; it occurs in platinum ores and as a free metal (native metal) with osmium in osmiridium, a natural alloy that includes platinum, ruthenium, and rhodium.
It is alloyed with platinum for jewelry and used for watch bearings and in scientific instruments. It was named in 1804 by English chemist Smithson Tennant (1761–1815) for its iridescence in solution.
Sinonimi: Pt | atomic number 78
ETYM New Lat., from Spanish platina, from plata silver, Late Lat. plata a thin plate of metal. Related to Plate, Platina.
A heavy precious metallic element; gray-white and resistant to corroding; occurs in some nickel and copper ores and is also found native in some deposits; SYN. Pt, atomic number 78.
A noble metal which in its pure form is the negative wire of Type R and Type S thermocouples.
Heavy, soft, silver-white, malleable and ductile, metallic element, symbol Pt, atomic number 78, atomic weight 195.09. It is the first of a group of six metallic elements (platinum, osmium, iridium, rhodium, ruthenium, and palladium) that possess similar traits, such as resistance to tarnish, corrosion, and attack by acid, and that often occur as free metals (native metals). They often occur in natural alloys with each other, the commonest of which is osmiridium. Both pure and as an alloy, platinum is used in dentistry, jewelry, and as a catalyst.
Sinonimi: Au | atomic number 79
ETYM AS. gold; akin to Dutch goud, OS. and German gold, Icel. gull, Swed. and Dan. guld, Goth. gulth, Russ. and Old Slav. zlato; prob. akin to Eng. yellow. Related to Yellow, Gild.
1. A soft yellow malleable ductile (trivalent and univalent) metallic element; occurs mainly as nuggets in rocks and alluvial deposits; reacts with few chemicals but is attacked by chlorine and aqua regia; SYN. Au, atomic number 79.
2. Coins made of gold.
3. Great wealth.
Shiny, yellow, ductile and very malleable, metallic element, symbol Au (from Latin aurum, “gold”), atomic number 79, atomic weight 197. It occurs in nature frequently as a free metal (see native metal) and is highly resistant to acids, tarnishing, and corrosion. Pure gold is the most malleable of all metals and is used as gold leaf or powder, where small amounts cover vast surfaces, such as gilded domes and statues.
The elemental form is so soft that it is alloyed for strength with a number of other metals, such as silver, copper, and platinum. Its purity is then measured in carats on a scale of 24 (24K = pure gold; 18K = 75% gold). It is used mainly for decorative purposes (jewelry, gilding) but also for coinage, dentistry, and conductivity in electronic devices.
Gold has been known and worked from ancient times, and currency systems were based on it in Western civilization, where mining it became an economic and imperialistic goal. In 1988 the three leading gold-producing countries were: South Africa, 563 tons; US, 186 tons; and Australia, 138 tons. In 1989 gold deposits were found in Greenland with an estimated yield of 11 tons per year.
The name is very old and derives from the Germanic form of Indo-European ghel, “to shine” or “to gleam”.
ETYM Latin Mercurius; akin to merx wares.
Or quicksilver; Heavy, silver-gray, metallic element, symbol Hg (from Latin hydrargyrum), atomic number 80, relative atomic mass 200.59. It is a dense, mobile liquid with a low melting point (-38.87şC/-37.96şF). Its chief source is the mineral cinnabar, HgS, but it sometimes occurs in nature as a free metal.
Its alloys with other metals are called amalgams (a silver-mercury amalgam is used in dentistry for filling cavities in teeth). Industrial uses include drugs and chemicals, mercury-vapor lamps, arc rectifiers, power-control switches, barometers, and thermometers.
Mercury is a cumulative poison that can contaminate the food chain, and cause intestinal disturbance, kidney and brain damage, and birth defects in humans. (The World Health Organization’s “safe” limit for mercury is 0.5 milligrams of mercury per kilogram of muscle tissue). The discharge into the sea by industry of organic mercury compounds such as dimethylmercury is the chief cause of mercury poisoning in the latter half of the 20th century. Between 1953 and 1975, 684 people in the Japanese fishing village of Minamata were poisoned (115 fatally) by organic mercury wastes that had been dumped into the bay and had accumulated in the bodies of fish and shellfish.
The element was known to the ancient Chinese and Hindus, and is found in Egyptian tombs of about 1500 BC. It was named by the alchemists after the fast-moving god, for its fluidity.
Mercury forms an amalgam with gold and so is used in gold mining to extract gold from low-grade deposits. Each year 250–300 metric tons are used in the Amazon basin alone. In 1990 mercury concentrations in edible fish close to the mining sites were 10 times greater than the WHO recommended limits for human consumption.
A heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures; SYN. quicksilver, Hg, atomic number 80.
ETYM Quick living + silver; -- so called from its fluidity; cf. German quecksilber, Latin argentum vivum. Related to Quick.
Old name for mercury.
Another name for the element mercury.
The metal mercury; -- so called from its resemblance to liquid silver. SYN. quick-silver.
Sinonimi: Tl | atomic number 81
ETYM New Lat., from Greek, young or green shoot or branch, twig. So called from a characteristic bright green line in its spectrum.
Soft, bluish white, malleable, metallic element, symbol Tl, atomic number 81, atomic weight 204.37. It is a poor conductor of electricity. Its compounds are poisonous and are used as insecticides and rodent poisons; some are used in the optical-glass and infrared-glass industries and in photocells.
Discovered spectroscopically 1861 by its green line, thallium was isolated and named by William Crookes 1861.
A soft gray malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores; SYN. Tl, atomic number 81.
A bluish-white soft malleable ductile plastic but inelastic heavy metallic element found mostly in combination and used especially in pipes, cable sheaths, batteries, solder, and shields against radioactivity
Sinonimi: Bi | atomic number 83
ETYM German bismuth, wismuth: cf. French bismuth.
Hard, brittle, reddish white metallic element, used in alloys and, as carbonate, for dyspepsia, etc.
Hard, brittle, pinkish-white, metallic element, symbol Bi, atomic number 83, atomic weight 208.98. It has the highest atomic number of all the stable elements (the elements from atomic number 84 up are radioactive). Bismuth occurs in ores and occasionally as a free metal (native metal). It is a poor conductor of heat and electricity, and is used in alloys of low melting point and in medical compounds to soothe gastric ulcers. The name comes from the Latin besemutum, from the earlier German Wismut.
A heavy brittle diamagnetic trivalent metallic element (resembles arsenic and antimony chemically); usually recovered as a by-product from ores of other metals; SYN. Bi, atomic number 83.
Sinonimi: Po | atomic number 84
ETYM New Lat. So named after Poland, in Latin form Polonia, one of the discoverers being a Pole.
Radioactive, metallic element, symbol Po, atomic number 84, atomic weight 210. Polonium occurs in nature in small amounts and was isolated from pitchblende. It is the element having the largest number of isotopes (27) and is 5,000 times as radioactive as radium, liberating considerable amounts of heat. It was the first element to have its radioactive properties recognized and investigated.
Polonium was isolated in 1898 from the pitchblende residues analyzed by French scientists Pierre and Marie Curie, and named for Marie Curie's native Poland.
A radioactive metallic element that is similar to tellurium and bismuth; occurs in uranium ores but can be produced by bombarding bismuth with neutrons in a nuclear reactor; SYN. Po, atomic number 84.
Sinonimi: At | atomic number 85
A highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium; SYN. At, atomic number 85.
Radioactive element of the halogen group.
Nonmetallic, radioactive element, symbol At, atomic number 85, atomic weight 210. It is a member of the halogen group, and is very rare in nature. Astatine is highly unstable, with at least 19 isotopes; the longest lived has a half-life of about eight hours.
Sinonimi: Rn | atomic number 86
Gaseous emanation of radium.
A radioactive gaseous element formed by the disintegration of radium; the heaviest of the inert gasses; occurs naturally (especially in areas over granite) and is considered a hazard to health; SYN. Rn, atomic number 86.
Colorless, odorless, gaseous, radioactive, nonmetallic element, symbol Rn, atomic number 86, atomic weight 222. It is grouped with the inert gases and was formerly considered non-reactive, but is now known to form some compounds with fluorine. Of the 20 known isotopes, only three occur in nature; the longest half-life is 3.82 days.
Radon is the densest gas known and occurs in small amounts in spring water, streams, and the air, being formed from the natural radioactive decay of radium. Ernest Rutherford discovered the isotope Rn-220 in 1899, and Friedrich Dorn (1848–1916) in 1900; after several other chemists discovered additional isotopes, William Ramsay and R W Whytlaw-Gray isolated the element, which they named niton in 1908. The name radon was adopted in the 1920s.
The average radon radiation level found in a study of 40 British limestone caves was 2,900 Bequerels per cubic meter. This compares with the National Radiological Protection Board's set level of 200 Bequerels per cubic meter, at which removal of radon from homes is recommended. The highest levels were found in the Giant's Hole in Derbyshire, with values of around 155,000 Bequerels per cubic meter during the summer, which is the highest level ever recorded from a natural limestone cave. This compares with a maximum level of 54,000 Bequerels per cubic meter found in a limestone cave in the US. Levels up to 2.8 million Bequerels per cubic meter were recorded in abandoned mines in SW England—14,000 times the NRPB action level for homes.
Sinonimi: Fr | atomic number 87
Radioactive metallic element, symbol Fr, atomic number 87, atomic weight 223. It is one of the alkali metals and occurs in nature in small amounts as a decay product of actinium. Its longest-lived isotope has a half-life of only 21 minutes. Francium was discovered and named in 1939 by Marguérite Perey to honor her country.
A radioactive element of the alkali-metal group discovered as a disintegration product of actinium; SYN. Fr, atomic number 87.
Sinonimi: Ra | atomic number 88
ETYM New Lat., from Latin radius ray.
Rare radioactive metallic element found in pitchblende, etc.
An intensely radioactive metallic element that occurs in minute amounts in uranium ores; SYN. Ra, atomic number 88.
White, radioactive, metallic element, symbol Ra, atomic number 88, atomic weight 226.02. It is one of the alkaline-earth metals, found in nature in pitchblende and other uranium ores. Of the 16 isotopes, the commonest, Ra-226, has a half-life of 1.622 years. The element was discovered and named in 1898 by Pierre and Marie Curie, who were investigating the residues of pitchblende.
Radium decays in successive steps to produce radon (a gas), polonium, and finally a stable isotope of lead. The isotope Ra-223 decays through the uncommon mode of heavy-ion emission, giving off carbon-14 and transmuting directly to lead. Because radium luminesces, it was formerly used in paints that glowed in the dark; when the hazards of radioactivity became known its use was abandoned, but factory and dump sites remain contaminated and many former workers and neighbors contracted fatal cancers.
A radioactive element of the actinide series; found in uranium ores
Sinonimi: Ac | atomic number 89
ETYM Greek aktis, aktin ray.
Rare radio-active element.
White, radioactive, metallic element, the first of the actinide series, symbol Ac, atomic number 89, atomic weight 227; it is a weak emitter of high-energy alpha particles.
Actinium occurs with uranium and radium in pitchblende and other ores, and can be synthesized by bombarding radium with neutrons. The longest-lived isotope, Ac-227, has a half-life of 21.8 years (all the other isotopes have very short half-lives). Actinium was discovered in 1899 by the French chemist André Debierne.
A radioactive element of the actinide series; found in uranium ores; SYN. Ac, atomic number 89.
Sinonimi: Th | atomic number 90
ETYM New Lat. Related to Thorite.
Dark-gray, radioactive, metallic element of the actinide series, symbol Th, atomic number 90, atomic weight 232.038. It occurs throughout the world in small quantities in minerals such as thorite and is widely distributed in monazite beach sands. It is one of three fissile elements (the others are uranium and plutonium), and its longest-lived isotope has a half-life of 1.39 x 1010 years. Thorium is used to strengthen alloys. It was discovered by Jöns Berzelius 1828 and was named by him after the Norse god Thor.
A soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands; SYN. Th, atomic number 90.
Sinonimi: protoactinium | Pa | atomic number 91
A short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead; SYN. protoactinium, Pa, atomic number 91.
Silver–gray, radioactive, metallic element of the actinide series, symbol Pa, atomic number 91, atomic weight 231.036. It occurs in nature in very small quantities, in pitchblende and other uranium ores. It has 14 known isotopes; the longest-lived, Pa-231, has a half-life of 32,480 years.
The element was discovered in 1913 (Pa-234, with a half-life of only 1.2 minutes) as a product of uranium decay by Kasimir Fajans and O Göhring; other isotopes were found in later years and the name was officially adopted in 1949, although it had been in use since 1918.
Sinonimi: U | atomic number 92
ETYM New Lat., from Uranus the planet. Related to Uranus.
Hard, lustrous, silver-white, malleable and ductile, radioactive, metallic element of the actinide series, symbol U, atomic number 92, atomic weight 238.029. It is the most abundant radioactive element in the Earth's crust, its decay giving rise to essentially all radioactive elements in nature; its final decay product is the stable element lead. Uranium combines readily with most elements to form compounds that are extremely poisonous. The chief ore is pitchblende, in which the element was discovered by German chemist Martin Klaproth 1789; he named it after the planet Uranus, which had been discovered 1781.
Small amounts of certain compounds containing uranium have been used in the ceramics industry to make orange-yellow glazes and as mordants in dyeing; however, this practice was discontinued when the dangerous effects of radiation became known.
Uranium is one of three fissile elements (the others are thorium and plutonium). It was long considered to be the element with the highest atomic number to occur in nature. The isotopes U-238 and U-235 have been used to help determine the age of the Earth.
Uranium-238, which comprises about 99% of all naturally occurring uranium, has a half-life of 4.51 x 109 years. Because of its abundance, it is the isotope from which fissile plutonium is produced in breeder nuclear reactors. The fissile isotope U-235 has a half-life of 7.13 x 108 years and comprises about 0.7% of naturally occurring uranium; it is used directly as a fuel for nuclear reactors and in the manufacture of nuclear weapons.
A heavy toxic silvery-white radioactive metallic element; occurs in many isotopes; used for nuclear fuels and nuclear weapons; SYN. U, atomic number 92.
Sinonimi: Np | atomic number 93
ETYM New Lat.
One of the transuranic elements.
Silvery, radioactive metallic element of the actinide series, symbol Np, atomic number 93, atomic weight 237.048. It occurs in nature in minute amounts in pitchblende and other uranium ores, where it is produced from the decay of neutron-bombarded uranium in these ores. The longest-lived isotope, Np-237, has a half-life of 2.2 million years. The element can be produced by bombardment of U-238 with neutrons and is chemically highly reactive.
It was first synthesized in 1940 by us physicists E McMillan (1907–) and P Abelson (1913–), who named it for the planet Neptune (since it comes after uranium as the planet Neptune comes after Uranus).
Neptunium was the first transuranic element to be synthesized.
A radioactive transuranic metallic element; found in trace amounts in uranium ores; a by-product of the production of plutonium; SYN. Np, atomic number 93.
Sinonimi: Pu | atomic number 94
A radioactive transuranic element that is similar to uranium; found in minute quantities in uranium ores but is usually synthesized in nuclear reactors; 13 isotopes are known, including plutonium 239; SYN. Pu, atomic number 94.
A highly toxic, heavy, radioactive metallic element. There are 15 isotopes of plutonium, of which only five are produced in significant quantities: plutonium-238, -239, -240, -241, and -242. Plutonium-239 is the most important plutonium isotope as it is f
One of the transuranic elements, product of decay of neptunium, used in the atomic bomb.
Silvery-white, radioactive, metallic element of the actinide series, symbol Pu, atomic number 94, atomic weight 239.13. It occurs in nature in minute quantities in pitchblende and other ores, but is produced in quantity only synthetically. It has six allotropic forms (see allotropy) and is one of three fissile elements (elements capable of splitting into other elements—the others are thorium and uranium). The element has awkward physical properties and is the most toxic substance known.
Its fissile isotope Pu-239 is usually made in breeder reactors by bombarding uranium-238 with neutrons. Because Pu-239 is so easily synthesized from abundant uranium, it has been produced in large quantities (hundreds of thousands of pounds) by the weapons industry. It has a long half-life (24,000 years) during which time it remains highly toxic. It is dangerous to handle, difficult to store, and impossible to dispose of—it has become a human-made menace of global proportions. According to a us Department of Energy report Dec 1994, the conditions in which it is stored across the us pose a threat to both workers in the nuclear weapons industry and the general public.
Plutonium was first produced in 1940 by Glenn Seaborg and his team at the University of California at Berkeley, by bombarding uranium with deuterons; this was the second transuranic element synthesized (after neptunium). It was named by them for the planet Pluto, since it comes after neptunium as the planet Pluto comes after Neptune.
Sinonimi: Am | atomic number 95
Artificial element (No. 95), made by bombarding uranium or plutonium with helium ions.
A radioactive transuranic metallic element; discovered by bombarding uranium with helium atoms; SYN. Am, atomic number 95.
Radioactive metallic element of the actinide series, symbol Am, atomic number 95, atomic weight 243.13; it was first synthesized 1944. It occurs in nature in minute quantities in pitchblende and other uranium ores, where it is produced from the decay of neutron-bombarded plutonium, and is the element with the highest atomic number that occurs in nature. It is synthesized in quantity only in nuclear reactors by the bombardment of plutonium with neutrons. Its longest-lived isotope is Am-243, with a half-life of 7,650 years.
The element was named by Glenn Seaborg, one of the team who first synthesized it in 1944, after the United States of America. Ten isotopes are known.
Sinonimi: Cm | atomic number 96
One of the transuranic elements.
A radioactive transuranic metallic element; produced by bombarding plutonium with helium nuclei; SYN. Cm, atomic number 96.
Synthesized, radioactive, metallic element of the actinide series, symbol Cm, atomic number 96, atomic weight 247. It is produced by bombarding plutonium or americium with neutrons. Its longest-lived isotope has a half-life of 1.7 x 107 years.
Curium is used to generate heat and power in satellites or in remote places. Named in 1946 for Pierre and Marie Curie by Glenn Seaborg, it was first synthesized in 1944 by Seaborg at the University of California at Berkeley, by analogy with the corresponding lanthanide, gadolinium (see periodic table of the elements).
Sinonimi: Bk | atomic number 97
A radioactive transuranic element; discovered by bombarding americium with helium; SYN. Bk, atomic number 97.
radioactive, metallic element made artificially.
Synthesized, radioactive, metallic element of the actinide series, symbol Bk, atomic number 97, atomic weight 247.
It was first produced 1949 by Glenn Seaborg and his team, at the University of California at Berkeley, US, after which it is named.
Sinonimi: Cf | atomic number 98
Synthesized, radioactive, metallic element of the actinide series, symbol Cf, atomic number 98, atomic weight 251. It is produced in very small quantities and used in nuclear reactors as a neutron source. The longest-lived isotope, Cf-251, has a half-life of 800 years.
It is named for the state of California, where it was first synthesized in 1950 by Glenn Seaborg and his team at the University of California at Berkeley.
A radioactive transuranic element; discovered by bombarding curium with alpha particles; SYN. Cf, atomic number 98.
Abbreviation for confer (Latin “compare”).
A radioactive transuranic element produced by bombarding plutonium with neutrons; SYN. Es, E, atomic number 99.
Synthesized, radioactive, metallic element of the actinide series, symbol Es, atomic number 99, atomic weight 254.
It was produced by the first thermonuclear explosion, in 1952, and discovered in fallout debris in the form of the isotope Es-253 (half-life 20 days). Its longest-lived isotope, Es-254, with a half-life of 276 days, allowed the element to be studied at length. It is now synthesized by bombarding lower-numbered transuranic elements in particle accelerators. It was first identified by A Ghiorso and his team who named it in 1955 after Albert Einstein, in honor of his theoretical studies of mass and energy.
Sinonimi: Fm | atomic number 100
Synthesized, radioactive, metallic element of the actinide series, symbol Fm, atomic number 100, atomic weight 257. Ten isotopes are known, the longest-lived of which, Fm-257, has a half-life of 80 days. Fermium has been produced only in minute quantities in particle accelerators.
It was discovered in 1952 in the debris of the first thermonuclear explosion. The element was named 1955 in honor of US physicist Enrico Fermi.A radioactive transuranic metallic element produced by bombarding plutonium with neutrons; SYN. Fm, atomic number 100.
Synthesized, radioactive metallic element of the actinide series, symbol Md, atomic number 101, atomic weight 258. It was first produced by bombardment of Es-253 with helium nuclei. Its longest-lived isotope, Md-258, has a half-life of about two months. The element is chemically similar to thulium. It was named by the US physicists at the University of California at Berkeley who first synthesized it 1955 after the Russian chemist Mendeleyev, who in 1869 devised the basis for the periodic table of the elements.
A radioactive transuranic element synthesized by bombarding einsteinium with alpha particles; SYN. Md, Mv, atomic number 101.
Sinonimi: No | atomic number 102
Synthesized, radioactive, metallic element of the actinide series, symbol No, atomic number 102, atomic weight 259. It is synthesized by bombarding curium with carbon nuclei.
It was named in 1957 after the Nobel Institute in Stockholm, Sweden, where it was claimed to have been first synthesized. Later evaluations determined that this was in fact not so, as the successful 1958 synthesis at the University of California at Berkeley produced a different set of data. The name was not, however, challenged. In 1992 the International Unions for Pure and Applied Chemistry and Physics (IUPAC and IUPAP) gave credit to Russian scientists in Dubna for the discovery of nobelium.
A radioactive transuranic element synthesized by bombarding curium with carbon ions; 7 isotopes are known; SYN. No, atomic number 102.
Sinonimi: Lw | atomic number 103
A radioactive transuranic element synthesized from californium; SYN. Lw, atomic number 103.
Synthesized, radioactive, metallic element, the last of the actinide series, symbol Lr, atomic number 103, relative atomic mass 262. Its only known isotope, Lr-257, has a half-life of 4.3 seconds and was originally synthesized at the University of California at Berkeley 1961 by bombarding californium with boron nuclei. The original symbol, Lw, was officially changed 1963.
The element was named for Ernest Lawrence (1901–1958), the US inventor of the cyclotron.
In 1992 the International Unions for Pure and Applied Chemistry and Physics (IUPAC and IUPAP) gave credit to Russian scientists in Dubna for the joint discovery of lawrencium.
Name proposed by Soviet scientists for the element currently known as unnilquadium (atomic number 104), to honor Soviet nuclear physicist Igor Kurchatov (1903–1960).
A radioactive transuranic element which has been synthesized; SYN. Rf, kurchatovium, Ku, unnilquadium, Unq, element 104, atomic number 104.
Synthesized radioactive element of the transactinide series, atomic number 106, atomic weight 263. It was first synthesized 1974 in the US and given the temporary name unnilhexium. The discovery was not confirmed until 1993. It was officially named 1994 after New Zealand physicist Ernest Rutherford.
The University of California, Berkeley, bombarded californium with oxygen nuclei to get isotope 263; the Joint Institute for Nuclear Research, Dubna, Russia, bombarded lead with chromium nuclei to obtain isotopes 259 and 260.
Sinonimi: Unh | element 106 | atomic number 106
A transuranic element; SYN. Unh, element 106, atomic number 106.
Temporary identification assigned to the element seaborgium 1974–1994.
Sinonimi: Uns | element 107 | atomic number 107
A transuranic element that has not been found in nature; SYN. Uns, element 107, atomic number 107.
Synthesized, radioactive element of the transactinide series, symbol Uns, atomic number 107, atomic weight 262. It was first synthesized by the Joint Institute for Nuclear Research in Dubna, Russia, in 1976; in 1981 the Laboratory for Heavy Ion Research in Darmstadt, Germany, confirmed its existence.