Important Terms

1. Kinetic molecular model explains the three states of matter assuming that

• matter is made up of particles called molecules.
• the molecules remain in continuous motion.
• molecules attract each other.

At very high temperatures, the collision between atoms and molecules tears off their electrons. Atoms become positive ions. This ionic state of matter is called the plasma-the fourth state of matter.

Density is the ratio of mass to volume of a substance. The density of water is 
$1000 kgm^{-3}$.