COMPOUNDS AND ELEMENTS. 11 



say, seventy odd marbles, it is no matter for wonder that 

 there are some two hundred and fifty thousand different 

 molecules. A substance is x molecules, and a molecule is 

 a little building of which the atoms are the bricks. We 

 may now re-define our definitions. 



A Molecule is the smallest particle of a substance that 

 can exist in a free state, and which has the same composi- 

 tion as any larger mass of the substance. 



An Atom is the smallest particle of an element that exists 

 in any molecule. 



A Compound is a substance whose molecule contains two 

 or more kinds of atoms. 



An Element is a substance whose molecule contains only 

 one kind of atom. 



&F 



