Oxygen

Element 8 · Nonmetal

Specimen

Atomic number: 8
Atomic mass: 15.999
State at room temperature: Gas
Melting point: -218.8 °C
Boiling point: -183 °C
Density: 0.001429 g/cm³
Discovered: 1774

Atomic mass from IUPAC.¹ Other physical data from PubChem.²

Can I eat it?

In food and water: Your body needs it. Oxygen is the most common element in the human body. It is in water and in food molecules such as glucose. ³

The atom

Shell	Electrons
1 (K)	2
2 (L) outermost	6
Total	8

Configuration [He] 2s² 2p⁴

2s ↑ ↓

2p ↑ ↓ ↑ ↑

Oxygen-16
Protons	8
Neutrons	8
Mass number	16

A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 8 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the He core, with one arrow per electron.

Related elements

Sources

1

IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

The atomic mass shown for the 84 elements that have a standard atomic weight.
2

National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

Electron configuration, melting and boiling points, density and discovery year for all 118 elements.
3
OpenStax, Rice University, 2022. Anatomy and Physiology 2e, section 2.1: Elements and Atoms: The Building Blocks of Matter .
- beginning with the most abundant: oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)
- When two hydrogen atoms each share their single electron with oxygen, covalent bonds are formed, resulting in a molecule of water
4

National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.

Specimen

Can I eat it?

The atom

Related elements

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Sources