Oxygen
nonmetalProperties
| Property | Value |
|---|---|
| Atomic Mass | 15.999 amu |
| Category | nonmetal |
| Group | 16 |
| Period | 2 |
| Electron Configuration | 1s2 2s2 2p4 |
| Electronegativity | 3.44 (Pauling) |
| Oxidation States | -2, -1, 2 |
| Melting Point | 54.36 K (-218.8 °C) |
| Boiling Point | 90.188 K (-183.0 °C) |
| Density | 0.001429 g/cm³ |
| Discovered By | Joseph Priestley (1774) |
About Oxygen
Oxygen is the second-most electronegative element (3.44 on Pauling, behind only fluorine), which makes it the workhorse oxidizer in nearly every reaction you care about — combustion, corrosion, mitochondrial respiration, the basic oxygen furnace. Around half the Earth's crust by mass is oxygen, locked into silicates and oxides, and 21% of the atmosphere is O₂. The dioxygen molecule is itself a chemical curiosity: ground-state O₂ is a triplet diradical, which is why it's slow to react with closed-shell organics at room temperature even though the thermodynamics scream go. Excited singlet O₂ is a different beast entirely — a pericyclic reagent that does ene reactions and [4+2] additions. The third allotrope, ozone (O₃), absorbs in the Hartley band and shields the surface from short-wavelength UV. Lavoisier coined the name from oxys + genes (acid-former) on the wrong assumption that all acids needed it, but the name stuck. Industrial O₂ comes from cryogenic distillation of air; medical and welding cylinders and basic-oxygen-furnace blast lances all draw from the same column.
Fun Fact
Ground-state O₂ is a triplet diradical — two unpaired electrons in degenerate π* orbitals — which is why air doesn't oxidize most organics at room temperature even though the thermodynamics say it should. Get oxygen into its singlet excited state and the whole story changes; singlet O₂ does Diels-Alder and ene reactions like an ordinary closed-shell electrophile.
Common Uses
- Basic oxygen furnace lancing in primary steelmaking (decarburizing pig iron)
- Cryogenic LOX as the oxidizer in liquid-fuel rocket engines (Merlin, RS-25)
- Medical oxygen therapy for hypoxemia, COPD exacerbations, and surgical anesthesia
- Oxy-fuel and oxy-acetylene cutting/welding for ferrous metals
- Aeration in activated-sludge wastewater treatment to drive nitrification