Chemical Bonding and Structure of Matter
What you must know
Distinguish ionic, covalent (polar and non-polar), metallic and intermolecular bonding. Use electronegativity difference to judge bond polarity and predict molecular shape with VSEPR (linear, trigonal planar, tetrahedral, trigonal pyramidal, bent). Apply hybridisation (sp, sp², sp³) and recognise that lone pairs compress bond angles. Relate structure type to physical properties: melting point, conductivity, solubility. Know the crystal classes - ionic, molecular, covalent network, metallic - and the hydrogen bond as an unusually strong dipole interaction.
Traps
- Assuming any polar bond gives a polar molecule; symmetry can cancel dipoles (CO₂, CCl₄).
- Confusing bond polarity with bond strength.
- Forgetting that network covalent solids (diamond, SiO₂) sublime or melt very high, while molecular solids melt low.
- Misreading VSEPR when lone pairs are present: NH₃ is pyramidal, H₂O is bent, not tetrahedral.
Worked example
Predict the shape of SF₄. Sulfur has 6 valence electrons; four S–F bonds use four, leaving one lone pair. Five electron domains give trigonal bipyramidal electron geometry; the lone pair occupies an equatorial site, so the molecular shape is a see-saw. Rule of thumb: count domains first, then place lone pairs to minimise repulsion (equatorial before axial).