Ideal Gas
Definition
A simplified model of a gas where particles are tiny points that never attract or repel each other. Real gases behave like this at low pressure and high temperature.
Technical definition
An ideal gas is a theoretical gas of point particles with no intermolecular forces and perfectly elastic collisions, obeying PV = nRT exactly. Real gases approximate ideal behavior at low pressure and high temperature, deviating near condensation points.
Example
Helium at room temperature and atmospheric pressure follows PV = nRT within about 0.1 percent, close enough that chemists treat it as ideal.
Common confusion
No gas is truly ideal: it is a model. It fails for gases near liquefaction or at very high pressures, where particle volume and attractions matter.