Theoretical chemistry tries to explain data from chemistry experiments. It uses mathematics and computers. Theoretical chemistry predicts what happens when atoms combine to form molecules. It also predicts chemical properties (characteristics) of molecules. An important part of theoretical chemistry is quantum chemistry. This is using quantum mechanics to understand valency (the number of bonds formed by an atom of an element). Other important parts include molecular dynamics, statistical thermodynamics and theories of electrolyte solutions, reaction networks, polymerization and catalysis.