18. Explain how the ions of the elements Al (Z = 13) and S (Z = 16) are formed
An aluminium atom has 13 electrons and 3 valence electrons on the outer shell. When an aluminium atom loses three valence electrons, the atom forms a positively charged ion Al3+. In contrast to aluminium, sulphur contains 16 electrons and has free orbitals. Sulphur can accept additional electrons resulting in the formation of negatively charged ions. If sulphur accepts two electrons it forms ion S2-.