Nitrogen vs. Oxygen

Wait, can someone explain to me how the Nitrogen (N2) molecules are larger than the Oxygen (O2) molecules when Nitrogen has a smaller atomic mass displayed on the periodic table of elements? Nitrogen is 14 g/mol while Oxygen is 16 g/mol.

From what I recall, Nitrogen was used as it's lighter than Oxygen or Air (which is about 75% N2 anyways). The lighter weight means it takes less torque to spin the wheel. When the newest Generation Nissan GTR's came out they put N2 in their tires from the factory.