Oxygen is an element with the chemical symbol O and atomic number 8.

Oxygen is a very reactive element that easily forms compounds such as oxides.

Under standard temperature and pressure conditions two oxygen atoms join to form dioxygen (O₂), a colorless, tasteless and odorless gas.

Oxygen is essential to human life, it is found in the air we breathe and the water we drink (H₂0).

Oxygen makes up around 21% of the air you breathe. It is also the most common element in the Earth’s crust (around 47%) and the third most common element in the Universe (but far less than hydrogen and helium, the two most common).

The large amount of oxygen on Earth is supported by the oxygen cycle which involves the movement of oxygen between the air, living things and the Earth’s crust. Photosynthesis (a process that converts carbon dioxide into organic compounds using sunlight) plays a major role in this cycle.

Ozone (O₃) is an allotrope (different form) of oxygen that combines three oxygen atoms together. While ground level ozone is an air pollutant, the ozone layer in the Earth’s upper atmosphere provides protection from the suns harmful rays by filtering UV light.

The sun’s mass is made up of around 1% oxygen.

Between 1770 and 1780, Swedish pharmacist Carl Wilhelm Scheele, British clergyman Joseph Priestley and French chemist Antoine Laurent Lavoisier researched, documented and helped discover oxygen. The name oxygen was first used by Lavoisier in 1777.

Oxygen therapy is used as a common medical treatment. You may have seen patients on TV or in real life using an oxygen mask or nasal cannula (a plastic tube that fits behind the ears and delivers oxygen through the nostrils).

Oxygen has a number of other practical uses such as smelting metal from ore, water treatment, as an oxidizer for rocket fuel and a number of other industrial, chemical and scientific applications.

Concentrated oxygen promotes fast combustion. While a spark or heat is still needed to start a fire, having concentrated oxygen near various fuels can be very dangerous.