7(ii)
The diagram below illustrates the structures of two atoms P and Q.
What is the formula and mass of one mole of the compound formed when P and Q react together?
[At. wt of P is 23 and Q is 16]
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From the diagram, P has 11 protons (2, 8, 1) and is a monovalent metal, while Q has 8 protons (2, 6) and is a divalent non-metal. When they react, P loses one electron and Q gains two electrons, so two atoms of P combine with one atom of Q.
Formula of the compound = P2Q
Mass of one mole = 2 × (At. wt of P) + (At. wt of Q)
= 2 × 23 + 16
= 46 + 16
= 62 g
∴ The formula is P2Q and one mole has a mass of 62 g.