Oxygen (O)
Oxygen is the 8th element, a reactive nonmetal in the p-block. Its standard atomic weight is 15.999.
Oxygen
15.999
What the table records
- Atomic number
- 8
- Standard atomic weight
- 15.999
- Group
- 16
- Period
- 2
- Block
- p-block
- Category
- Reactive nonmetal
- [He] 2s2 2p4
- Valence electrons
- 6
- Typical valence
- 2
- Van der Waals radius
- 1.55 Å
- Covalent radius
- 0.66 Å
Molecules containing oxygen
The lightest named structures in this library that contain O.
Atomic oxygen
O · 16 g/mol
Hydroxide
HO- · 17.01 g/mol
Hydroxyl
HO · 17.01 g/mol
Water
H₂O · 18.02 g/mol
Hydrogen hydrate
H₄O · 20.03 g/mol
Carbon Monoxide
CO · 28.01 g/mol
Formaldehyde
CH₂O · 30.03 g/mol
Nitroxyl
HNO · 31.01 g/mol
Methoxide
CH₃O- · 31.03 g/mol
Oxygen
O₂ · 32 g/mol
Methanol
CH₄O · 32.04 g/mol
Hydroxylamine
H₃NO · 33.03 g/mol
How to read these numbers
The standard atomic weight is an average over the isotopes as they occur naturally, which is why it is rarely a whole number. It is the figure a molar mass calculation uses. Work in mass spectrometry wants the monoisotopic mass of a single isotope instead, which is a different number.
The two radii are not the same measurement. The covalent radius is half the distance between two bonded atoms of the element; the van der Waals radius is how close a non-bonded atom gets before repulsion takes over, and is always the larger. Space-filling models are drawn with the second, ball-and-stick models with the first — which is why the same molecule looks so different in the two.