Ideal gases and lattice structures

Last time

Before we start: last time, in Intermolecular forces and metallic bonding, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

A gas, a solid, and the rules they follow

A balloon of helium and a diamond ring are both made of atoms. The gas atoms move freely, almost without interacting. In diamond, every atom is locked into a rigid lattice. Two models explain them: the ideal gas, and the four types of giant or simple lattice.

The ideal gas

The molecules have negligible volume compared with the volume of the container. There are no intermolecular forces between the molecules. Collisions between molecules, and with the walls, are perfectly elastic. The molecules move randomly. A real gas behaves most like an ideal gas at high temperature and low pressure.

When a gas is not ideal

At low temperature, molecules move slowly, and intermolecular forces matter. At high pressure, the volume of the molecules is no longer negligible. A small molecule with few electrons has weak instantaneous dipole-induced dipole forces and a small volume. So helium behaves most like an ideal gas. A gas with strong forces, such as one with hydrogen bonds, deviates most.

The ideal gas equation

The equation is p V equals n R T. Pressure in pascals, volume in cubic metres, amount in moles, temperature in kelvin. R is the molar gas constant, 8.31 joules per kelvin per mole. Convert: cm cubed to m cubed by multiplying by ten to the minus six; kPa to Pa by multiplying by a thousand; Celsius to kelvin by adding 273.