WAEC Chemistry 2015 Paper

Concept:Van der Waals forces are the dominant intermolecular forces that act between neutral, non-polar covalent molecules.Explanation:Chlorine exists as a simple covalent molecule, $\mathrm{Cl}_2$.It is non-polar because both atoms have equal electronegativity.Therefore, the only significant forces between separate chlorine molecules are weak London dispersion forces, which are a type of Van der Waals forces.Ammonium chloride, $\mathrm{NH}_4\mathrm{Cl}$, and sodium chloride, $\mathrm{NaCl}$, are ionic compounds.In these solids, strong ionic bonds hold the ions together, not Van der Waals forces.Water, $\mathrm{H}_2\mathrm{O}$, is a polar molecule.It forms strong hydrogen bonds between its molecules, and these hydrogen bonds are much stronger than ordinary Van der Waals forces.Hence, among the given options, only chlorine has Van der Waals forces as its dominant intermolecular force.Answer:B. Chlorine