---
title: "Oxygen (O): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/oxygen.html
description: "Oxygen (O), element 8: atomic mass 15.999, electron configuration [He] 2s² 2p⁴, group 16, period 2, p-block reactive nonmetal. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
8O15.999

# Oxygen (O) – element 8

Oxygen is a chemical element with the symbol **O** and atomic number **8**. It is a reactive nonmetal in group 16 (chalcogens), period 2 of the periodic table (p-block), and is a gas at room temperature.

Oxygen (O) has atomic number 8, atomic mass 15.999 u and electron configuration [He] 2s2 2p4.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Oxygen facts

| Symbol | O |
| --- | --- |
| Atomic number | 8 |
| Atomic mass | 15.999 u (g/mol) |
| Category | reactive nonmetal |
| Group | group 16 (chalcogens) |
| Period | 2 |
| Block | p-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 2s2 2p4 |
| Noble-gas notation | [He] 2s2 2p4 |
| Electrons per shell | 2, 6 |
| Valence electrons | 6 |

## Bohr model and shells

Oxygen has 8 electrons in 2 shells: 2, 6. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 54.36 K (-218.8 °C) |
| --- | --- |
| Boiling point | 90.188 K (-183.0 °C) |
| Density | 1.429 g/L |
| Electronegativity (Pauling) | 3.44 |
| Electron affinity | 140.976 kJ/mol |
| Ionization energies | 1313.9, 3388.3, 5300.5 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Carl Wilhelm Scheele |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing O.

## Position in the periodic table

Tap any element to open its page.

## Molecules with oxygen

- [Acetic acid](https://www.moldraw.com/molecules/acetic-acid.html)
- [Acetone](https://www.moldraw.com/molecules/acetone.html)
- [Adrenaline](https://www.moldraw.com/molecules/adrenaline.html)
- [Alanine](https://www.moldraw.com/molecules/alanine.html)
- [Aspirin](https://www.moldraw.com/molecules/aspirin.html)
- [ATP](https://www.moldraw.com/molecules/atp.html)
- [Caffeine](https://www.moldraw.com/molecules/caffeine.html)
- [Carbon dioxide](https://www.moldraw.com/molecules/carbon-dioxide.html)
- [Cholesterol](https://www.moldraw.com/molecules/cholesterol.html)
- [Citric acid](https://www.moldraw.com/molecules/citric-acid.html)
- [Cortisol](https://www.moldraw.com/molecules/cortisol.html)
- [Cytosine](https://www.moldraw.com/molecules/cytosine.html)

Rotate each one in 3D, or draw your own structure in [MolDraw](https://www.moldraw.com/).

## Frequently asked questions

### What is the atomic mass of oxygen?

The atomic mass of oxygen is 15.999 u, so one mole of oxygen atoms weighs 15.999 g.

### What is the electron configuration of oxygen?

Oxygen has 8 electrons: 1s² 2s² 2p⁴, or [He] 2s² 2p⁴ in noble-gas notation. Electrons per shell: 2, 6.

### How many valence electrons does oxygen have?

Oxygen has 6 valence electrons (group 16).

### Is oxygen a metal?

No. Oxygen is a nonmetal (reactive nonmetal).

### Where is oxygen on the periodic table?

Oxygen is in group 16 (chalcogens), period 2, in the p-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.