Oxygen is a chemical element with atomic number 8, represented by the symbol O. The name oxygen was coined in 1777 by Lavoisier. Its name derives from the Greek word “oxys” meaning “sharp,” referring to the sharp taste of acids, and “genēs” meaning “producer.” It is a chalcogen and is highly reactive, forming compounds such as oxides with most other elements. Oxygen is also the name of the molecular compound O₂, also known as dioxygen, formed from two covalently linked oxygen atoms with a spin triplet electron configuration.

Oxygen is the third most abundant element in the universe by mass, after hydrogen and helium, and the most abundant element by mass in the Earth’s crust. Dioxygen as a gas makes up 20.9 % of the volume of Earth’s atmosphere and is also present in the form of water vapor and CO₂. Oxygen makes up 49.2 % of the Earth’s crust by mass, mostly in the form of silicates, carbonates, and metal oxides, and is the major component of seawater at 88.8 % by...