Atomic Structure, Bonding and Chemical Reactions
Atomic structure, bonding and chemical reactions brings together electronic configuration, chemical bonding and quantitative reaction chemistry. The exam rewards precise use of the mole concept and correct ion charges.
Atomic structure
Atoms contain protons (relative mass 1, charge +1), neutrons (mass 1, charge 0) and electrons (mass about 1/1836, charge −1). Isotopes have the same proton number but different neutron numbers. Electrons fill orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d.
Bonding
Ionic bonding transfers electrons between metals and non-metals, giving high melting points and conductivity when molten. Covalent bonding shares electron pairs; molecular substances have weak intermolecular forces and low melting points. Metallic bonding involves delocalised electrons. Electronegativity differences explain polarity.
Moles and stoichiometry
n = m/M; one mole of gas occupies 22.4 dm³ at s.t.p.; concentration c = n/V. Balance equations before using mole ratios, and identify the limiting reagent.
Acids, redox and equilibrium
pH = −log₁₀[H⁺]. Oxidation is loss of electrons; reduction is gain. Le Chatelier's principle predicts the direction of shift when conditions change.
Worked example
5.3 g of Na₂CO₃ (M = 106 g mol⁻¹) is 0.050 mol. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ needs 0.10 mol HCl. At 0.50 mol dm⁻³, V = n/c = 0.10/0.50 = 0.20 dm³ = 200 cm³.
Traps
Forgetting the 2:1 ratio, using mass instead of moles, and treating strong and weak acids as equally dissociated.