Under which conditions does a real gas stop behaving like an ideal gas?

1. An ideal gas is defined as having particles of zero volume with no forces between them. 2. At high pressure the particles are squeezed together and their own volume stops being negligible. 3. At low temperature the particles slow down and the attractive forces between them start to matter. 4. A real gas therefore behaves like an ideal gas except at high pressures and low temperatures. 5. Push the conditions far enough in that direction and the gas liquefies altogether. 6. Low pressure with high temperature is where the ideal picture works best, so that option is exactly backwards. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 7: Ideal gases_