• The mole is a fixed number of particles and refers to the amount, n, of substance.

• Masses of atoms are compared on a scale relative to 12C and are expressed as relative atomic mass (Ar) and relative formula/molecular mass (Mr).

• Molar mass (M) has the units g mol-1.

• The empirical formula and molecular formula of a compound give the simplest ratio and the actual number of atoms present in a molecule respectively.

• Calculation of the molar masses of atoms, ions, molecules and formula units.

• Solution of problems involving the relationships between the number of particles, the amount of substance in moles and the mass in grams.

• Interconversion of the percentage composition by mass and the empirical formula.

• Determination of the molecular formula of a compound from its empirical formula and molar mass.

• Obtaining and using experimental data for deriving empirical formulas from reactions involving mass changes.

• The value of the Avogadro’s constant (L or NA) is given in the data booklet in section 2 and will be given for paper 1 questions.

• The generally used unit of molar mass (g mol-1) is a derived SI unit.