Other examples of ionic bonding

2 marks · Hard

Explain why a bromide ion () has the same number of electrons as a krypton atom.

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Also accept: Bromine atom (Br) gains 1 electron to become Br–, making total electrons equal to krypton atom.; Br atom has 35 electrons, Br– has 36, same as krypton.

Common mistakes: States loses electron instead of gains; Compares number of protons

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Marking points

M1 · 1 mark · States that the bromine atom gains 1 electron to form Br–.

A1 · 1 mark · States that Br– has same number of electrons as krypton.

Worked solution

A bromine atom gains 1 electron to become Br–, giving it 36 electrons.

Krypton also has 36 electrons, so Br– is isoelectronic with krypton.