Chemical Bonding — Prelims Strategy

Prelims Strategy

Classify the structure before selecting a property. An ionic crystal, a molecular substance and an extended covalent network should not be treated as interchangeable categories. For conductivity questions, identify the mobile carrier and the physical state. Solid sodium chloride already contains ions; melting changes their mobility rather than creating charge for the first time.

For polarity, combine bond polarity with geometry. Opposing dipoles can cancel in a symmetric molecule. In shape questions, count bonding regions and lone pairs, then distinguish electron-domain arrangement from the positions of atoms. Water's four electron domains do not make its molecular shape tetrahedral.

For phase changes, ask whether molecules are being separated or chemically decomposed. Hydrogen bonding between water molecules differs from the covalent O–H bonds within each molecule. Finally, use diamond and graphite to check overbroad claims about covalent materials. A correct statement about many simple molecular substances may fail for an extended network or a material with delocalised electrons. Read the stated structure before applying the generalisation.