Electronic configurations and the periodic table

2 marks · Easy

An atom of chlorine has atomic number 17. Calculate the number of electrons in its second shell.

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8 (±0)

Also accept: eight

Common mistakes: 17 electrons; 7 electrons

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Marking points

M1 · 1 mark · Correctly deduces electronic configuration: 2,8,7.

A1 · 1 mark · States 8 electrons in the second shell.

Worked solution

Chlorine (atomic number 17):

First shell: 2 electrons

Second shell: 8 electrons

Third shell: 7 electrons (altogether: 2+8+7 = 17)

So the second shell has 8 electrons.