Carbon dioxide has one carbon atom and two oxygen atoms, and a molecular weight of 44 grams per mole (a certain number of molecules). The oxygen in the air is actually O 2, or molecular oxygen, with a molecular weight of 32.Hence, carbon dioxide has a higher density, or is heavier than oxygen. That is why you need to be careful with carbon dioxide. It can displace the oxygen in a room and lead to asphyxiation.ence, carbon dioxide has a higher density, or is heavier than oxygen. That is why you need to be careful with carbon dioxide. It can displace the oxygen in a room and lead to asphyxiation.