The periodic table

2 marks · Hard

The symbol for antimony is Sb. An atom of antimony has 51 protons and a mass number of 123. State the number of electrons and calculate the number of neutrons in a neutral atom of antimony.

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51 electrons; 72 neutrons

Also accept: electrons: 51; neutrons: 72

Common mistakes: Electrons: 123; Neutrons: 51

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Marking points

M1 · 1 mark · States electrons = 51 (neutral atom has equal numbers of electrons and protons).

A1 · 1 mark · Correctly calculates neutrons: 123 - 51 = 72.

Worked solution

Number of electrons = number of protons = 51 (because it is a neutral atom).