Electronic configuration of argon

Electrons in each shell

Argon has 18 electrons arranged as 2, 8, 8 across 3 shells, which is why it sits in period 3.

How to write it

Electrons fill orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p… Each s orbital holds 2 electrons, p holds 6 and d holds 10. Placing Argon's 18 electrons in that order gives 1s² 2s² 2p⁶ 3s² 3p⁶.

Argon at a glance

Atomic number	18
Symbol	Ar
Atomic mass	39.95 u
Group	18
Period	3
Block	p-block
Category	Noble gas
Valence electrons	8

Could you find argon in 6 guesses?Play Tatva, the free daily periodic table game

Other elements in group 18

Elements in the same group have the same number of outer electrons, which is why they behave alike.