 An atom is the basic unit of matter (make up elements)  If you break it any smaller it is no longer the element  Atoms are made up of smaller pieces called protons, electrons, and neutrons  Elements are made entirely of the same type of atom

 When two or more atoms are joined together they form a bond  There are two types of bonds between atoms, ionic and covalent

 Two or more atoms joined together form a compound  The two main types of compounds are molecules and salts  Molecules are formed from covalent bonds (shared electrons)  Salts are formed from ionic bonds (taken electrons)

 A third type of bonding, called hydrogen bonding, occurs between certain molecules  Very present in water