O
Oxygen
Element 8 · Reactive nonmetal
Oxygen (O)
Oxygen is a highly reactive gas that makes up 21% of the air and nearly half of Earth’s crust by mass. Animals need it to release energy from food.
- Reactive nonmetal
- Period 2
- Group 16
- p-block
- gas at room temperature
Key properties
- Atomic mass
- 15.999
- u
- Electron configuration
- [He] 2s2 2p4
- Melting point
- -218.8 °C
- 54.36 K
- Boiling point
- -183 °C
- 90.2 K
- Density
- 1.429 g/L
- Electronegativity
- 3.44
- Pauling
- Atomic radius
- 152 pm
- van der Waals
- 1st ionisation energy
- 13.618 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about oxygen
- 01
Oxygen is the most abundant element in Earth’s crust and in the human body by mass.
- 02
Liquid oxygen is pale blue and is attracted to a magnet.
- 03
Almost all of the oxygen in the air was produced by photosynthesis.
Applications
What is oxygen used for?
- Steelmaking
- Medical oxygen therapy
- Rocket oxidiser
- Water treatment
History
Discovery & name origin
Discovered by
Year
Where
Sweden and England
Name origin
Greek oxys + genes, “acid-former” — Lavoisier wrongly believed all acids contained oxygen.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 8
- Atomic mass
- 15.999 u
- Group
- 16
- Period
- 2
- Block
- p-block
- Electron configuration
- [He] 2s2 2p4
- Full configuration
- 1s2 2s2 2p4
- Electrons per shell
- 2, 6
- Electronegativity (Pauling)
- 3.44
- Electron affinity
- 1.461 eV
- Atomic radius (van der Waals)
- 152 pm
- Stable isotopes
- 3
Oxidation states
Highlighted: common oxidation states (-2).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st1,313.9
- 2nd3,388.3
- 3rd5,300.5
- 4th7,469.2
- 5th10,989.5
- 6th13,326.5
- 7th71,330
- 8th84,078
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Gas
- Melting point
- 54.36 K · -218.8 °C · -361.8 °F
- Boiling point
- 90.2 K · -183 °C · -297.3 °F
- Density
- 1.429 g/L
- Molar heat capacity
- —
- Appearance
- —
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Oxygen questions
What is O on the periodic table?
O is the symbol for oxygen, element 8 on the periodic table. It sits in group 16, period 2, in the reactive nonmetal category, and has an atomic mass of 15.999.
What is the atomic number of oxygen?
Oxygen has atomic number 8, so every oxygen atom has 8 protons in its nucleus. Its symbol is O and its atomic mass is 15.999.
Who discovered oxygen?
Oxygen was discovered by Carl Wilhelm Scheele and Joseph Priestley in 1774 (Sweden and England). The name comes from Greek oxys + genes, “acid-former” — Lavoisier wrongly believed all acids contained oxygen.
What is oxygen used for?
Oxygen is used for: steelmaking; medical oxygen therapy; rocket oxidiser; water treatment.
Is oxygen a metal?
No. Oxygen is classed as a reactive nonmetal.
What is the electron configuration of oxygen?
The electron configuration of oxygen is [He] 2s2 2p4. Its 8 electrons are arranged in shells as 2, 6.