Is air made 100% from atoms?

I know air is made up of roughly 78% nitrogen, 20% oxygen, etc.. but I would like to know what percentage of air is just space and has no atoms at all.




One way to answer this is to compare nitrogen gas at standard pressure and temperature to liquid nitrogen at 1 atm. The density ratio is about 1500. In the liquid, space is nearly filled by the N2 molecules, so it follows that the molecules in the gas only occupy 1/1500 of the total volume. Also, since the cube root of 1500 is about 12, it must be true that the typical distance between molecules is about 12 times the mean molecular diameter.


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**Air is mostly molecules not atoms and most of the space in a gas is empty**


Most of the gaseous components of air are not individual atoms but molecules (oxygen, nitrogen are diatomic, carbon dioxide and water vapour are triatomic). The only common single atom is argon (about 1% of the atmosphere by mole ratio).


But this is mostly irrelevant to the underlying question. Gases occupy far more space than the molecular size of the components of the gas. To a good approximation, all gases occupy just over 22 L of space at standard temperature and pressure whatever the molecule is. This is far larger (by a factor of 1000-2000 times the volume taken up by the molecules or atoms making up the gas if we use the normal size of the molecules (as 10ppb points out in their answer).


So most of the space in a gas is *not* "occupied" by anything at a given snapshot in time. But, remember, gas molecules move around quickly which is why they "fill" a space so a view at one moment in time is a misleading way to think about the issue.


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