Electronic configuration of aluminium

Electrons in each shell

Aluminium has 13 electrons arranged as 2, 8, 3 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 Aluminium's 13 electrons in that order gives 1s² 2s² 2p⁶ 3s² 3p¹.

Aluminium at a glance

Atomic number	13
Symbol	Al
Atomic mass	26.982 u
Group	13
Period	3
Block	p-block
Category	Post-transition metal
Valence electrons	3

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Other elements in group 13

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