Argon (Ar): electron configuration, atomic mass and facts
Argon (Ar) is element 18 of the periodic table, a noble gas in period 3, group 18. Its electron configuration is [Ne] 3s2 3p6, with electrons arranged in shells 2, 8, 8, and its standard atomic weight is 39.948 u.
💡 The third most common gas in air (about 0.93%).
▶ Watch Argon’s electrons orbit in the interactive periodic tableArgon at a glance
| Symbol | Ar |
|---|---|
| Atomic number | 18 |
| Atomic mass | 39.948 u |
| Category | Noble gas |
| Group | 18 |
| Period | 3 |
| Block | p-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 |
| Noble-gas shorthand | [Ne] 3s2 3p6 |
| Electrons per shell | 2, 8, 8 |
| Outer-shell electrons | 8 |
| Electronegativity (Pauling) | — |
| State at 20 °C | gas |
Where is Argon on the periodic table?
Argon is in period 3, group 18, in the p-block. The period number matches its 3 electron shells, and the block names the subshell its last electrons fill. In the same group, Neon sits directly above it and Krypton sits directly below it. Elements in one group have the same number of outer-shell electrons (8 here), which is why they react in similar ways.
How to work out the electron configuration of Argon
Put 18 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18). In shorthand, [Ne] stands for the 10 electrons of neon, giving [Ne] 3s² 3p⁶.
Frequently asked questions
What is the electron configuration of Argon?
The electron configuration of Argon (Ar) is 1s2 2s2 2p6 3s2 3p6. In noble-gas shorthand it is written [Ne] 3s2 3p6.
How many electrons does Argon have in each shell?
Argon has 18 electrons arranged in shells as 2, 8, 8. It has 8 electrons in its outer shell.
What is the atomic mass of Argon?
The standard atomic weight of Argon is 39.948 u, so one mole of Argon atoms has a mass of about 39.948 g.
Is Argon a metal?
No. Argon is a noble gas.
Explore nearby elements
More noble gass: Helium, Neon, Krypton, Xenon, Radon, Oganesson. See all elements on the periodic table.