Electronic configuration of chlorine

Electrons in each shell

Chlorine has 17 electrons arranged as 2, 8, 7 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 Chlorine's 17 electrons in that order gives 1s² 2s² 2p⁶ 3s² 3p⁵.

Chlorine at a glance

Atomic number	17
Symbol	Cl
Atomic mass	35.45 u
Group	17
Period	3
Block	p-block
Category	Halogen
Valence electrons	7

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Other elements in group 17

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