Oxygen (O)
Oxygen (symbol O) is the chemical element with atomic number 8: a nonmetal, a gas at 0 °C, with an atomic mass of 15.999 u. Discovered in 1774 (Carl Wilhelm Scheele and Joseph Priestley).
Oxygen is the gas our cells use to “burn” food and produce energy. It makes up 21% of the air, but above all nearly half the mass of the rocks in Earth's crust. Highly reactive, it combines with almost everything: rust and fire are both reactions with oxygen. Its presence in the atmosphere is the work of living organisms.
Key facts
- Atomic number
- 8
- Symbol
- O
- French name
- Oxygène
- Atomic mass
- 15.999 u
- Molar mass
- 15.999 g/mol
- Family
- Nonmetals
- Position
- period 2, group 16, p-block
- State at 0 °C
- Gas
- Melting point
- -218.8 °C
- Boiling point
- -183 °C
- Density
- 0.00143 g/cm³
- Electronegativity (Pauling)
- 3.44
- First ionization energy
- 1,314 kJ/mol
- Atomic radius
- 60 pm
- Electron configuration
- [He] 2s² 2p⁴
- Abundance in Earth's crust
- 461,000 ppm (1st most abundant element)
- Indicative price
- 0.15 $/kg (order of magnitude)
- Radioactive
- no
- Discovery
- 1774, Carl Wilhelm Scheele and Joseph Priestley
Origin of the name
From the Greek oxys (acid) and genes: “acid-former.”
What does oxygen look like?
A colorless, odorless gas. As a liquid, at −183 °C, it takes on a lovely pale blue tint and is attracted by a magnet.
Where is oxygen found?
The third most abundant element in the Universe. About 46% of the mass of Earth's crust (in silicates and oxides), 89% of the mass of water, 21% of air by volume. It is the most abundant element in the human body: about 65% of its mass, mostly as water.
Natural sources
- Air (21%)
- Water
- Quartz and silicates
- Metal oxides (hematite, bauxite)
How is oxygen produced?
It is produced industrially by distilling liquefied air, or by membrane or molecular-sieve separation for smaller needs. Industry separates more than 100 million tonnes a year, most of it destined for steelmaking.
What is oxygen used for?
- Steelmaking: removing carbon from pig iron to make steel.
- Oxygen therapy in hospitals.
- Oxy-acetylene welding and cutting.
- Rocket oxidizer (liquid oxygen).
- Water treatment and the chemical industry.
In everyday life
- The air you breathe
- Tap water
- Rust on a bike
- A candle flame
Role in living things
Vital to the respiration of almost all animals, plants and fungi: it serves as the final electron acceptor in our mitochondria. It is produced by photosynthesis in plants, algae and cyanobacteria, which release it by splitting water molecules.
Hazards of oxygen
Not flammable itself, it makes everything else burn fiercely: an oxygen-enriched atmosphere turns a spark into a blaze, as in the Apollo 1 accident in 1967. Breathed pure and under pressure, it becomes toxic to the lungs and nervous system.
Cosmic origin
- Supernovae: Forged in the cores of massive stars, then scattered when they explode.
History of oxygen
The Swede Carl Wilhelm Scheele discovered it around 1771–1772 but published late; the Englishman Joseph Priestley isolated it in 1774. It was Lavoisier who understood its role in combustion and respiration and named it oxygen, “acid-former,” wrongly believing it was part of every acid.
Did you know?
- About 2.4 billion years ago, oxygen produced by cyanobacteria flooded the atmosphere: the “Great Oxidation Event,” which wiped out many microbes.
- Liquid oxygen is magnetic: poured between the poles of a strong magnet, it stays suspended there.
- Ozone (O₃), made of three oxygen atoms, shields us from UV high in the atmosphere but irritates the lungs at ground level.
Isotopes of oxygen
Three stable isotopes. The ratio of oxygen-18 to oxygen-16 in ice and fossils is a genuine thermometer for past climates.
- oxygen-15: radioactive, half-life 2.04 min. Water labeled with oxygen-15 measures blood flow in the brain in PET scans.
- oxygen-16: 99.757% of natural oxygen, stable
- oxygen-17: 0.038% of natural oxygen, stable. The only oxygen isotope visible in NMR.
- oxygen-18: 0.205% of natural oxygen, stable. Raw material for fluorine-18 used in PET, and a gauge of past temperatures (paleoclimatology).
Common compounds
Water (H₂O) · Glucose (C₆H₁₂O₆) · Table sugar (C₁₂H₂₂O₁₁) · Alcohol (C₂H₅OH) · Caffeine (C₈H₁₀N₄O₂) · Atmospheric oxygen (O₂) · Ozone (O₃) · Urea (CO(NH₂)₂) · Citric acid (C₆H₈O₇) · Vitamin C (C₆H₈O₆) · Aspirin (C₉H₈O₄) · Paracetamol (C₈H₉NO₂) · Chlorophyll a (C₅₅H₇₂MgN₄O₅) · Hydroxyapatite (Ca₅(PO₄)₃(OH)) · Baking soda (NaHCO₃) · Vinegar (CH₃COOH) · Bleach (NaClO) · Caustic soda (NaOH) · Hydrogen peroxide (H₂O₂) · Limestone (CaCO₃) · Gypsum (plaster) (CaSO₄·2H₂O) · Carbon dioxide (CO₂) · Quartz (sand) (SiO₂) · Rust (Fe₂O₃) · Corundum (ruby, sapphire) (Al₂O₃) · Sulfur dioxide (SO₂) · Malachite (Cu₂CO₃(OH)₂) · Sulfuric acid (H₂SO₄) · Titanium dioxide (TiO₂) · Lithium cobalt oxide (LiCoO₂) · Lithium iron phosphate (LiFePO₄) · Uranium dioxide (UO₂) · Ammonium nitrate (NH₄NO₃)
Related elements
Same family (nonmetals): Hydrogen (H), Carbon (C), Nitrogen (N), Phosphorus (P), Sulfur (S), Selenium (Se).
Same column (group 16): Sulfur (S), Selenium (Se), Tellurium (Te), Polonium (Po), Livermorium (Lv).