There is only one significant force at work in chemical reactions: the electromagnetic force. There are four fundamental forces in the universe: gravity, the electromagnetic force, the weak nuclear force and the strong nuclear force. Gravity is too weak to affect chemical reactions much, seeing as chemical reactions involve the rearranging of tiny atoms. Also, the nuclear forces don't play a role in chemical reactions. If a nuclear force becomes involved, then you are dealing with a nuclear reaction and not a chemical reaction. Every facet of chemistry is the result of one force: the electromagnetic force. However, because of the quantum wave nature of particles, this force can take on many forms. In a strict sense, every manifestation of the electromagnetic force is unique, as it depends crucially on the arrangement of atoms, the state of their electrons, their temperature, etc. To foster better understanding, however, chemists place the different forms of the electromagnetic force into broad classes: