Fluorine.

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.

Oxygen.

ETYM French oxygène, 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.

An obsolete name for nitrogen.
Obsolete, nitrogen.

Nitrogen
In mathematics, variable used to denote an indefinite number.

ETYM Latin nitrum natron + -gen: cf. French nitrogène. Related to Niter.
Colorless, odorless, tasteless, gaseous, nonmetallic element, symbol N, atomic number 7, atomic weight 14.0067. It forms almost 80% of the Earth's atmosphere by volume and is a constituent of all plant and animal tissues (in proteins and nucleic acids). Nitrogen is obtained for industrial use by the liquefaction and fractional distillation of air. Its compounds are used in the manufacture of foods, drugs, fertilizers, dyes, and explosives.
Nitrogen has been recognized as a plant nutrient, found in manures and other organic matter, from early times, long before the complex cycle of nitrogen fixation was understood. It was isolated in 1772 by English chemist Daniel Rutherford (1749–1819) and named in 1790 by French chemist Jean Chaptal (1756–1832).
A common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues; SYN. N, atomic number 7.

Carbon

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.

Boron.

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.

Beryllium

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.

Lithium

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.

Helium

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 (-268.9ºC/-452ºF) and melting points (-272.2ºC/-458ºF) 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).

Alternate name for element.

Hydrogen.

ETYM Hydro-, 1 + -gen: cf. French hydrogène. 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).

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.