Lesson 1 Atom，Molecule，Ion and Element

The term state of matter refers to the physical forms in which matter exists: solid，liquid and gas. All substances in the world assume one of the three different states of matter. All matter，whether it is a gas，a liquid or a solid，can all be composed of fundamental units，such as atom，molecule，ion and element. These units are very helpful in understanding chemistry. This lesson will introduce the student to the general knowledge of these particles.