Why is there no oxygen in space?

On Earth, gravity holds things to the Earth. For example, if you jump up, you come down because gravity pulls you back. It is the same with gases like oxygen, they can’t get very far from the Earth because gravity pulls them back.
On planets or moons that have very low gravity, gases can escape and enter space. But space is so big, that whatever gases are found in space, gases spread out so fast, that they are so far apart from each other that we say there is no gas in space. What I really mean is that there is so little gas in space, not enough for us to use to breathe.

 

Space is a vacuum because there is so much space between galaxies, stars, and planets. All of the mass of the universe is caught up in stars (which is made up of galaxies) and planets. In between are almost unimaginable distances, where there is nothing but a few hydrogen atoms every cubic meter.