The unit in one line
The rules the rest of chemistry obeys: how much reacts with how much, how atoms are built and bonded, and which way a reaction goes and how fast. 17 of Chemistry's 50 questions over fourteen chapters, the joint-heaviest unit in the subject and the most numerical.
Read in this order
Fourteen chapters is four sittings, not one. They are grouped below in the order they build on each other.
First, the counting. Nothing later works without these.
- Basic concepts in chemistry (10 min) — atoms, molecules and valency, the radicals table, empirical and molecular formulae, balancing.
- Stoichiometry (12 min) — the gas laws that fix the mole, mole conversions, limiting reagent and percentage yield, with ten graded numericals.
Then the atom and the bond.
- Atomic structure (12 min) — Bohr's radius and energy, the hydrogen spectrum, the four quantum numbers and the filling order.
- Classification of elements and periodicity (10 min) — every trend across and down, and the exceptions that get asked.
- Chemical bonding and shape of molecules (15 min) — VSEPR shapes and angles, hybridisation, dipole moment, hydrogen bonding.
- Redox reactions (10 min) — oxidation numbers with the fractional cases, and both ways of balancing.
- States of matter (16 min) — the gas laws and real gases, liquids, and the unit cell with its packing numbers.
Then equilibrium, which is three chapters of one idea.
- Chemical equilibrium (11 min) — Kc and Kp, Le Chatelier applied to the Haber and Contact processes, degree of dissociation.
- Volumetric analysis (12 min) — equivalent weights, every concentration unit, and fourteen worked titration problems.
- Ionic equilibrium (14 min) — pH of every kind of solution, the common-ion effect, buffers, solubility product and salt hydrolysis.
Then the four that stand alone.
- Chemical kinetics (14 min) — order against molecularity, first-order half-life, Arrhenius and catalysis.
- Electrochemistry (15 min) — Faraday's laws, electrode potentials and the series, cells from the Daniell to the fuel cell.
- Chemical thermodynamics (16 min) — the first law and its sign convention, Hess cycles, entropy, and the four cases of Gibbs energy.
- Nuclear chemistry (13 min) — decay types and equations, half-life arithmetic, radioisotopes and carbon dating.
About 180 minutes in all. Mass defect and binding energy are not here: they belong to Modern and nuclear physics.
How it is asked
MEC sets the paper roughly half recall, a third understanding and a fifth application. Recall here is a shape and its angle, a catalyst and its conditions, the unit of a rate constant. Understanding is why the order of a reaction is not its molecularity, why ammonia is polar and nitrogen trifluoride barely is, or which way an equilibrium shifts on compression. Application is the arithmetic: a limiting reagent, a pH, a titre, an equivalent weight, a half-life, a Gibbs energy at a stated temperature.
Then practise
Each chapter has a fixed-length chapter test under Practice › Topics, drawn from questions written to that chapter's scope. Sit it after reading; a second sitting a week later shows whether it stuck.