Final answer:
Gas particles will get closer together when they are cold because they have less kinetic energy. As the temperature decreases, the gas behaves less ideally due to the prominence of intermolecular forces bringing the particles closer.
Step-by-step explanation:
When gas particles are cold, the particles will get closer together because they have less energy. In the context of thermal physics, when gas particles cool down, their average kinetic energy decreases. This reduction in energy means the particles slow down and the attractive forces between them become more prominent, pulling them closer together. If the cooling continues, the gas could condensate into a liquid or even solidify, further illustrating the decrease in energy and particle motion.
Under conditions of low temperature and high pressure, gases behave less ideally, as the assumptions used in the ideal gas law become less applicable. The particles have lower kinetic energy relative to the attractive forces and are thus less effective in overcoming these attractions, leading to a denser phase where particles are closer together.