Today in chemistry I learned that the particles in a gas are considered to be small, hard spheres with an insignificant volume. Within a gas, the particles are relatively far apart compared with the distance between particles in a liquid or solid. Between the particles, there is empty space. No attractive or repulsive forces exist between the particles. The motion of the particles in a gas is rapid, constant, and random. As a result, gases fill their containers regardless of the shape and volume of the containers. All collisions between particles in a gas are perfectly elastic.