Knowra Oxygen Oxygen Oxygen is the chemical element with atomic number 8, symbol O. It is a reactive nonmetal that makes up about 21% of Earth’s atmosphere and occurs in water, rocks, and living organisms.
Oxygen atom : An atom with eight protons in its nucleus; neutral oxygen atoms have eight electrons. Its electron arrangement explains why oxygen commonly forms two bonds.
Oxidation–reduction reaction : A chemical reaction in which electrons move between substances, changing their oxidation states. Oxygen often accepts electrons as other substances are oxidized.
Great Oxidation Event : A major rise in atmospheric oxygen around 2.4 billion years ago, recorded in ancient rocks. Oxygenic photosynthesis eventually drove this profound change in Earth’s atmosphere.
Medical oxygen therapy : The clinical administration of oxygen to treat or prevent low oxygen levels in body tissues. Its therapeutic use depends on oxygen’s role in human respiration and blood oxygenation.
Sulfur : A reactive nonmetallic element with atomic number 16 that forms many compounds and several allotropes. Sulfur shares oxygen’s group in the periodic table but has distinct bonding and biological roles.
Oxygen isotopes : Variants of oxygen atoms with different numbers of neutrons, including oxygen-16, oxygen-17, and oxygen-18. Their differing masses make oxygen useful in tracing environmental and geological histories.
Combustion : A rapid exothermic reaction, commonly between a fuel and an oxidizer, that releases heat and often light. Atmospheric O₂ supports many familiar combustion reactions without itself being a fuel.
Oxygenic photosynthesis : Photosynthesis that uses water as an electron source and releases molecular oxygen. This metabolism is the principal biological source of free O₂ on Earth.
Oxygen production : Industrial processes that separate or generate oxygen for medical, manufacturing, and research use. Air separation and electrolysis supply oxygen beyond what can be gathered from the atmosphere.
Nitrogen : A nonmetallic element with atomic number 7 that makes up most of Earth’s atmosphere as N₂. Nitrogen dominates the atmosphere, while oxygen is more reactive and supports aerobic metabolism.
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