Most familiar matter exists in three forms, solid, liquid, and gas. An ice cube, for example is a solid, it just sits there and doesn't move. You can see it. Apply some heat and the ice cube melts into water. You can still see it, but as a liquid, it spreads around and sloshes if it is in a glass. If you weigh the ice cube and the amount of water they should be the same. No matter has vanished. Now heat the water. It seems to disappear. It turns into water vapor, a gas. But if you could collect all the water vapor and weigh it you would find it weighs the same amount. So nothing has been lost, it just changes form. The fact that you can't see it just means that your eyes are not sensitive enough. Certain scientific instruments can, though. The water vapor will expand and dissipate if you don't confine it to a bottle or box, but it does take up space. For example if you blow up a balloon and squeeze it you can feel that there is something inside it. That's air. The air that we breathe is made up of several kinds of gasses, mainly Nitrogen. About 21 percent is Oxygen, the stuff that we can't live without. Several other kinds of gasses are there too.
Why isn't there air in outer space? It's because the earth's gravity keeps most of it close to home.
LeeH
(published on 05/16/2013)