The world of particles is so small that it is difficult to use normal measurements to describe it. New concepts and ideas are needed to be able to deal comfortably with a world that we cannot see, but which, when scaled up, produces the surroundings with which we are familiar.
Atoms of different elements combine in fixed ratios to form compounds, which have different properties from their component elements.
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.
Applications and skills
Deduction of chemical equations when reactants and products are specified.
Application of the state symbols (s), (l), (g) and (aq) in equations.
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
In Chapter 3.2