Oxygen O

Discovery

Oxygen has two discoverers and a famous naming dispute. The Swedish pharmacist Carl Wilhelm Scheele produced the gas around 1771–1772 by heating substances such as mercuric oxide and potassium nitrate, and called it 'fire air', but his book describing the work did not appear until 1777.

Meanwhile, on 1 August 1774, the English clergyman and chemist Joseph Priestley focused sunlight through a lens onto mercuric oxide and collected a gas in which a candle burned brilliantly and a mouse lived longer than in ordinary air. He published first, interpreting the gas as 'dephlogisticated air'.

It was Antoine Lavoisier who understood what the gas really was. Through careful weighing he showed that combustion and rusting involve combining with this component of air, overturning the phlogiston theory, and he named it oxygène in 1777.

Origin of the name

Lavoisier built the name from the Greek oxys (sharp, acid) and -genes (forming), because he wrongly believed that oxygen was an essential part of all acids. The misconception was later corrected, but the name stuck. The symbol is O.

Main uses

• Steelmaking: blowing pure oxygen through molten iron burns off excess carbon; this is the largest industrial use.
• Medicine: oxygen therapy supports patients with breathing difficulties and is used in anaesthesia.
• Cutting and welding: oxy-acetylene torches reach temperatures above 3,000 °C.
• Chemicals and water treatment: oxygen and ozone are used to make chemicals, treat wastewater and disinfect drinking water.
• Rocketry: liquid oxygen is the oxidiser for many launch vehicles.

Isotopes

Oxygen has three stable isotopes: oxygen-16 (about 99.76 percent), oxygen-17 and oxygen-18. Because water containing oxygen-18 evaporates slightly less readily, the ratio of oxygen-18 to oxygen-16 in ice cores, shells and sediments serves as a record of past temperatures. Enriched oxygen-18 water is the starting material for making fluorine-18 for PET scans. The radioactive oxygen-15, with a half-life of about 2 minutes, is itself used in PET studies of blood flow.

In everyday life

Oxygen accounts for about 65 percent of the human body by mass, mostly in water. In the upper atmosphere it forms ozone, which absorbs harmful ultraviolet light. Breathing pure oxygen for long periods can damage the lungs, and oxygen-enriched environments make materials burn far more fiercely, so home oxygen users must keep away from open flames.