1Complete the electron arrangement of these elements and use it to find their valency: hydrogen, boron, magnesium, chlorine and calcium.
2Using the steps of the criss-cross method, write the molecular formula of magnesium oxide.
3Write the molecular formula of each of these compounds: potassium chloride, calcium chloride, ammonia, carbon dioxide and water.
4What are the valence shell, the valence electron and the valency? Explain each with an example.
5Why is the valency of argon 0?
6Sulphur has 6 electrons in its outer shell, yet its valency is only 2. Why?
7The swap gives \( \mathrm{Mg}_2\mathrm{O}_2 \). Why is this written as \( \mathrm{MgO} \)?
8Aluminium has valency 3 and oxygen has valency 2. Write the molecular formula of aluminium oxide.