oxygène

Oxygène (in English, oxygen) is a chemical element with symbol O and atomic number 8. It is a highly reactive nonmetal that exists as a pale blue diatomic gas at room temperature. The most common allotrope, O2, makes up about 21% of Earth's atmosphere and is essential for aerobic respiration. Ozone (O3) is another allotrope present in the stratosphere, where it absorbs ultraviolet radiation.

In the Earth's crust, oxygen accounts for about 46% by mass, mostly in oxides. It is a major component of water (H2O) and many minerals. In biology, oxygen is required for cellular respiration, allowing cells to generate energy. In humans, oxygen is transported by hemoglobin in red blood cells.

Production and applications: industrial production of oxygen is dominated by fractional distillation of liquefied air and by air separation units; oxygen is widely used in steelmaking, chemical synthesis, welding, medical therapy, and environmental remediation.

Safety and environment: oxygen supports combustion; materials burn more vigorously in pure oxygen atmospheres. Ozone in the stratosphere blocks UV radiation; however, ground-level ozone is a pollutant. Controlled oxygen therapy is used in medicine.

History: oxygen was identified in 1774 by Carl Wilhelm Scheele and Joseph Priestley; the name oxygen was proposed by Antoine Lavoisier, who helped establish its role in combustion and respiration.