Electronic configuration of sodium

Electrons in each shell

Sodium has 11 electrons arranged as 2, 8, 1 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 Sodium's 11 electrons in that order gives 1s² 2s² 2p⁶ 3s¹.

Sodium at a glance

Atomic number	11
Symbol	Na
Atomic mass	22.990 u
Group	1
Period	3
Block	s-block
Category	Alkali metal
Valence electrons	1

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Other elements in group 1

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