Everything from the 3 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
An ideal gas obeys pV = nRT exactly. The kinetic model assumes the molecules are in rapid random motion, have negligible volume compared with the container, have no intermolecular forces, and collide elastically. Real gases behave most ideally at low pressure and high temperature, where the molecules are far apart and move fast. In pV = nRT use SI units: p in Pa, V in m3, T in K and R = 8.31 J K−1 mol−1. Rearranged with n = m ÷ M, the equation gives M = mRT ÷ pV, a way to find Mr of a gas or volatile liquid.
Keep M in g mol−1 by leaving the mass in grams. And check your answer is sensible: an Mr of 0.058 or 58 000 for a simple liquid means a volume or pressure was not converted. A temperature in °C instead of K is the other classic slip.
In a liquid the particles are close together but disordered, moving randomly and sliding past each other while intermolecular forces still hold them. Melting overcomes only some of those forces, but vaporisation separates the particles completely, so the enthalpy change of vaporisation is much larger than that of fusion (water: 41 against 6.0 kJ mol−1). In a closed container, evaporation and condensation reach a dynamic equilibrium; the pressure of the vapour then is the vapour pressure. It rises with temperature, and a liquid boils when its vapour pressure equals the external pressure.
Evaporation happens at any temperature, from the surface only; boiling happens at one temperature for a given pressure, throughout the liquid. And when explaining vapour pressure, say the equilibrium is dynamic: both processes continue at equal rates, they do not stop.
A crystalline solid has a regular three-dimensional arrangement of particles called a lattice. There are four types: giant ionic (NaCl, MgO: ions held by ionic bonds), giant metallic (Cu: cations in delocalised electrons), giant molecular or covalent (diamond, graphite, graphene, SiO2: atoms joined by covalent bonds throughout) and simple molecular (I2, ice, C60: molecules held by weak intermolecular forces). To explain a property, name the particles, the force that must be overcome, and how strong it is.
For a giant molecular solid, melting breaks covalent bonds; for a simple molecular solid it overcomes only intermolecular forces. Mixing these up is the most common error in this section. Graphite conducts through delocalised electrons, not ions.