In chemistry, we often explain the states of matter in terms of the kinetic molecular theory (KMT). The word kinetic refers to motion and the kinetic molecular theory suggests that atoms and molecules are always in motion. The energy associated with this motion is termed kinetic energy.
Point out the following about solids: The particles (atoms or molecules) are attracted to each other. The particles (atoms or molecules) vibrate but do not move past one another. The solid retains its shape.
They are not always in motion. They are always in motion if and only if the temperature of the surroundings is greater than absolute zero ( 0 K ).
Not only are molecules really small but they are in constant motion. The motion is called “thermal motion” because it's caused by temperature. Increase the temperature around them and the molecules move faster.
