Kiseonik, kisik, najrasprostranjeniji element u prirodi, sastojak vazduha, vode, većine minerala i gotovo svih jedinjenja što sačinjavaju građu biljaka i životinja.
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.