Medical Oxygen

Oxygen is a member of the chalcogengroup on the periodic table and is a highly reactivenonmetallic element that readily forms compounds (notably oxides) with almost all other elements. Oxygen is a strong oxidizing agent and has the second highest electronegativity of all the elements (only fluorine has a higher electronegativity).^[1] By mass, oxygen is the third most abundant element in the universe after hydrogen and helium^[2] and the most abundant element by mass in the Earth's crust, making up almost half of the crust's mass.^[3] Free oxygen is too chemically reactive to appear on Earth without the photosynthetic action of living organisms, which use the energy of sunlight to produce elemental oxygen from water. Elemental O₂ only began to accumulate in the atmosphere after the evolutionary appearance of these organisms, roughly 2.5 billion years ago.^[4] Diatomic oxygen gas constitutes 20.8% of the volume of air