Chemical Fundamentals: Structure, Properties and Reactions
What you must understand
Start with the periodic table as a predictive tool: position determines valence electron count, which determines bonding and hence properties. You need to move fluently between electron configuration, Lewis structures, VSEPR shapes, and intermolecular forces, because most exam questions chain these ideas together. Know the distinction between ionic, covalent, metallic and network covalent substances, and be able to justify conductivity, melting point and solubility from structure rather than memory.
Balance equations and perform stoichiometric calculations confidently, including limiting reagent, percentage yield and molar volume of gases at STP (22.71 L mol⁻¹ under the current definition) and the ideal gas law. Understand enthalpy of combustion and neutralisation as experimental quantities, and the difference between exothermic and endothermic processes in terms of bond breaking and forming.
Traps to watch
- Empirical vs molecular formula: combustion analysis gives empirical ratios; you must be told or calculate molar mass to reach the molecular formula.
- Limiting reagent: divide moles by stoichiometric coefficient before comparing.
- VSEPR lone pairs: lone pairs compress bond angles (CH₄ 109.5°, NH₃ 107°, H₂O 104.5°).
- Conductivity: graphite conducts but diamond does not, despite both being carbon - delocalised electrons matter, not bonding type alone.
Worked example
4.60 g of ethanol (M = 46.07 g mol⁻¹) burns completely. Moles = 4.60/46.07 = 0.0999 mol. From C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O, CO₂ = 2 × 0.0999 = 0.200 mol, volume at STP = 0.200 × 22.71 = 4.54 L.
Rule of thumb: always convert to moles first, apply the mole ratio, then convert to the requested unit - never ratio masses directly.