OXYGEN

(O), nonmetallic chemical element of Group VIa of the periodic table. Oxygen is a colourless, odourless, tasteless gas, the most plentiful element in the Earth's crust; its most important compound is water. Oxygen was discovered about 1772 by a Swedish chemist, Carl Wilhelm Scheele, who obtained it by heating potassium nitrate, mercury(II) oxide, and many other substances. An English chemist, Joseph Priestley, independently discovered oxygen in 1774 by the thermal decomposition of mercury(II) oxide and published his findings the same year, three years before Scheele published. A French chemist, Antoine Lavoisier, first recognized the gas as an element (177580), coined its name, and (in opposition to the phlogiston theory) explained combustion as a union of oxygen with the burning material.