---
title: "Argon (Ar): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/argon.html
description: "Argon (Ar), element 18: atomic mass 39.948, electron configuration [Ne] 3s² 3p⁶, group 18, period 3, p-block noble gas. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
18Ar39.948

# Argon (Ar) – element 18

Argon is a chemical element with the symbol **Ar** and atomic number **18**. It is a noble gas in group 18 (noble gases), period 3 of the periodic table (p-block), and is a gas at room temperature.

Argon (Ar) has atomic number 18, atomic mass 39.948 u and electron configuration [Ne] 3s2 3p6.

[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)

## Argon facts

| Symbol | Ar |
| --- | --- |
| Atomic number | 18 |
| Atomic mass | 39.948 u (g/mol) |
| Category | noble gas |
| Group | group 18 (noble gases) |
| Period | 3 |
| Block | p-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 |
| Noble-gas notation | [Ne] 3s2 3p6 |
| Electrons per shell | 2, 8, 8 |
| Valence electrons | 8 |

## Bohr model and shells

Argon has 18 electrons in 3 shells: 2, 8, 8. 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 | 83.81 K (-189.3 °C) |
| --- | --- |
| Boiling point | 87.302 K (-185.8 °C) |
| Density | 1.784 g/L |
| Electron affinity | -96 kJ/mol |
| Ionization energies | 1520.6, 2665.8, 3931 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Lord Rayleigh |

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 Ar.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of argon?

The atomic mass of argon is 39.948 u, so one mole of argon atoms weighs 39.948 g.

### What is the electron configuration of argon?

Argon has 18 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶, or [Ne] 3s² 3p⁶ in noble-gas notation. Electrons per shell: 2, 8, 8.

### How many valence electrons does argon have?

Argon has 8 valence electrons (group 18).

### Is argon a metal?

No. Argon is a nonmetal (noble gas).

### Where is argon on the periodic table?

Argon is in group 18 (noble gases), period 3, 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.