WAEC Chemistry 2017 Paper

Concept:The strength of a metallic bond depends on the number of valence electrons contributed by each atom and the charge of the cation formed.Explanation:Metallic bonding arises from the attraction between positively charged metal ions and the sea of delocalised electrons.A higher positive charge on the metal ion creates a stronger electrostatic attraction.Among the given metals, aluminium, $_{13}\mathrm{Al}$, has the valence electronic configuration $3s^2 3p^1$, so it loses 3 electrons to form $\mathrm{Al}^{3+}$.Magnesium, $_{12}\mathrm{Mg}$, forms $\mathrm{Mg}^{2+}$; sodium, $_{11}\mathrm{Na}$, forms $\mathrm{Na}^{+}$; and potassium, $_{19}\mathrm{K}$, forms $\mathrm{K}^{+}$.Since $\mathrm{Al}^{3+}$ has the highest charge, its metallic bond is the strongest.Answer:A. $_{13}\mathrm{Al}$