Air may feel a lot like space because it does not put up much resistance to moving through it or displacing it by putting something else in its place. But the reality is that air does not have space, air actually fills space. Space has nothing in it, but air is space filled with gases, nitrogen, oxygen, argon, carbon dioxide in particular.

Air is made of a bunch of molecules that are moving around very fast. These molecules bounce off of each other and resist being compressed. Because of this, air wants to take up a lot of space, even though if you were to magically stop all the molecules from moving, there would still be a lot of empty space.

Did you know the air we breath is made mostly of nitrogen and not oxygen? Nitrogen and Oxygen molecules (along with a few other gas molecules) bounce around us in our atmosphere. There is no boundary for our outer atmosphere but the heavier molecules like oxygen and nitrogen stay close to Earth's surface and we are able to breath! Other parts of our atmosphere extend out into space so air has infinite space!

Air "has" (or perhaps, occupies) space ( Baylor College video proving this ) because air is made of matter, and matter occupies space. "Occupying" space may be difficult to define at this level, but one way is to say that volume is occupied by some piece of matter when another piece of matter cannot be at the same location. That is, if one were to try to force one piece of matter into space already occupied by some other matter, then the two bits of matter would repel and either the first piece would be pushed away so the new could move into its place, or the first piece would remain and the new piece could only be placed nearby. Explaining this repulsion and reasons that matter has space requires rather advanced physics.

The Pauli exclusion principle states that two particles cannot occupy the same quantum state. Quantum states and quantum physics is far too large a topic for this question, but one result is that all electrons of atoms cannot simply fall toward the nucleus, which would be their lowest energy state. Instead, electrons must exist at successively greater distances, meaning that atoms will "fill" some finite volume. Another (related) result is that electrons of two atoms cannot be in the same place. In accordance with the Pauli exclusion principle, the electrons and atoms will "repel" each other, essentially refusing to be in the same location, giving the sensation of solidity to matter. Thus the atoms that make up air occupy space, and since the atmosphere is made up of many many atoms which cannot be in the same location, air also takes up space.

What we call air is made of many small things called molecules - oxygen, nitrogen, carbon dioxide are all made of these molecules. Molecules affect one another just like we humans affect one another: They have mass and volume, and they cannot take up space that another molecule has already taken, just as I as a human cannot literally be in the space in which you're standing/sitting/lying down. Furthermore, these molecules move fast, run into one another, and everything around them. Therefore, even though they're very small, they take up more space than just their small volumes would have allowed them to if they were not moving very fast. Together, the number and speed of these molecules make their apparent volume much larger than their literal volume.

The air molecules are far apart. The molecules of nitrogen gas and oxygen gas and water vapor move all around and bump into each other, but they're not crowded together, like water molecules in liquid water or in ice. Liquid nitrogen is very very cold. When it expands into nitrogen gas, it takes up almost 700 times as much space as it did when it was liquid nitrogen.

Liquid Nitrogen Facts.

Air is not space. Air is atoms and molecules in the gas phase that are very low density than most other matter, but air is still matter, not empty space.