COMPOSITION OF MATTER 7 



destroy the identity or change the composition of the 

 molecule. When a chemical change occurs, the atoms 

 are combined in a different way and a new molecule is 

 produced. The molecule is the smallest particle of mat- 

 ter that can exist and retain its identity or individuality. 

 Physics and chemistry are closely related sciences, but 

 each deals with a different kind of change. Compounds 

 are composed of molecules, and molecules of atoms. 

 Atoms never exist free, but unite to form molecules. If 

 a substance contains in its molecule only atoms of one 

 kind, it is an element. If there are present atoms of 

 more than one kind, it is a compound. Life processes 

 are dependent largely upon the physical and chemical 

 changes continually taking place in nature. 



