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Sub-shells

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Each electron shell is divided into sub-shells.

• The first shell has one sub-shell (called the s sub-shell).

• The second shell has two sub-shells (called the s and p sub-shells).

• The third shell has three sub-shells (called the s, p and d sub-shells).

• The fourth shell has four sub-shells (called the s, p, d and f sub-shells).