Metals and non-metals in the periodic table

2 marks · Easy

Calcium (Ca) forms an oxide when it reacts with oxygen. The formula of the oxide is either CaO or CaO2. Using your knowledge of the periodic table, determine which formula is correct for the oxide of calcium and state how many oxygen atoms are present in the formula.

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The correct formula of calcium oxide is CaO. It contains 1 atom of oxygen. atoms (±0)

Also accept: 1

Common mistakes: 2

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Marking points

M1 · 1 mark · Identifies CaO as the correct formula for the oxide of calcium.

A1 · 1 mark · States there is 1 atom of oxygen in CaO.

Worked solution

Group 2 elements form oxides with the formula MO, where M is the metal. Calcium is in Group 2, so its oxide is CaO.

There is 1 atom of oxygen in CaO.