Oxygen (symbol O, atomic number 8) is a non-metallic chemical element from the chalcogen family. In the form of dioxygen (O₂), it makes up about 21% of Earth's atmosphere and plays a fundamental role in cellular respiration and combustion reactions.
Molecular oxygen (O₂) is essential for aerobic cellular respiration in most eukaryotic organisms. It acts as the final electron acceptor in the mitochondrial electron transport chain, enabling efficient ATP production. In its absence, cells rely on fermentation, which yields much less energy. Consequence of a deficit: Hypoxia, metabolic distress, and rapid cell death. Oxygen is thus critical for short-term survival.
1771: Carl Wilhelm Scheele's Experiments
The Swedish chemist Scheele produces oxygen by heating various metal oxides but publishes his results late.
1774: Joseph Priestley Isolates the Gas
The English chemist obtains pure oxygen from heated mercury oxide (HgO). He speaks of "dephlogisticated air."
1785: Antoine Lavoisier Defines Its Nature
Lavoisier rejects the phlogiston theory and demonstrates that oxygen is an element involved in respiration and combustion. He introduces the name "oxygen," from the Greek oxys (acid) and genes (engender), mistakenly believing it was necessary for the formation of acids.
Electron configuration: 1s² 2s² 2p⁴
Valence electrons: 6 (p⁴ configuration), tendency to complete its octet through two covalent bonds.
Isotopes:
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