There are two reactants needed to form sodium chloride, NaCl. Sodium, which is a solid under normal conditions, and chlorine, a diatomic gas under normal conditions must react to form the NaCl which will be a solid under these conditions. The reaction proceeds according to the following
2Na(s) + Cl2(g) --> 2NaCl(s)
The chlorine must be shown as a diatomic molecule because that is how it exists in nature. Therefore, we must include a coefficient of two in front of the sodium and the sodium chloride to achieve a balanced chemical equation.
The links below show you more information about the two reactants as well as NaCl.