How do particles differ in states of matter?

Answer 1

The primary difference in particles in different sates of matter is their kinetic energy. Atoms and molecules in solids will have less kinetic energy (the energy of "vibration" or motion) than those same atoms and molecules will in the liquid state. In a gas, the atoms or molecules will have more energy than in the liquid state, and much more than in the solid state. That's the key here.

There is a bit more to this in that the atoms and molecules in solids will be "bound together" more than in the liquid state. The solid has "structure" or "shape" because of the inter-atomic or intermolecular bonds. That changes in a liquid as liquids don't hold their shape, which you knew as a part of the definition of that state of matter. It's easy to see that the atoms and molecules will be even less strongly bound together in a gaseous state, and for the same reason. But atomic or molecular kinetic energy will keep atoms or molecules apart if it is high. And it will allow them to "come together" to interact and "hook up" if it is low.