Oxygen

Antoine Lavoisier

Goddard and Rocket

Oxygen molecule orbitals diagram

Liquid oxygen in a magnet

Chemical element with symbol O and atomic number 8

Oxygen is a chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, and is classified as a highly reactive nonmetal and a strong oxidizing agent. Oxygen readily forms oxides with most elements and many compounds.

Properties

• Atomic number: 8
• Symbol: O
• Atomic mass: 15.999 u
• Electron configuration: 1s² 2s² 2p⁴
• Standard state: Gas at room temperature
• Appearance: Colorless, odorless gas

Oxygen exists in several allotropes, the most common of which is diatomic oxygen (O₂), essential for cellular respiration in most aerobic organisms. Another allotrope, ozone (O₃), plays a critical role in absorbing ultraviolet radiation in the Earth's stratosphere.

Abundance and Occurrence

Oxygen is:

• The most abundant element in the Earth's crust by mass
• The second-most abundant component of the Earth's atmosphere (approximately 21%)
• The third-most abundant element in the universe, after hydrogen and helium

It is found in water (H₂O), silicates, oxides, and in all known life forms.

Biological Role

Oxygen is essential for life in many forms:

• Required for aerobic respiration in plants, animals, fungi, and most bacteria
• Produced as a byproduct of photosynthesis in plants, algae, and cyanobacteria

Oxygen is transported in the bloodstream of vertebrates by the protein hemoglobin.

Industrial and Medical Uses

Oxygen has a wide array of applications, including:

• Medical oxygen therapy and life support systems
• Oxy-fuel welding and cutting
• Steel and chemical manufacturing
• Water treatment and environmental monitoring
• Rocket propellants and high-altitude breathing equipment

History

Oxygen was independently discovered in the 1770s by:

• Carl Wilhelm Scheele in Sweden (before 1773)
• Joseph Priestley in England (1774)

The name "oxygen" was coined by Antoine Lavoisier, who helped establish its role in combustion and respiration, disproving the phlogiston theory.

Oxygen

• Priestley and Fuseli
  Priestley and Fuseli
• Oxygen molecule
  Oxygen molecule
• 
  Liquid oxygen in a beaker
• 
  Evolved star fusion shells
• Sea surface oxygen
  Sea surface oxygen
• Phanerozoic Climate Change
  Phanerozoic Climate Change
• 
  Simple photosynthesis overview

See Also

• Periodic table
• Photosynthesis
• Respiration
• Ozone layer