Is air matter?

( source:http://i.treehugger.com/images/2007/10/24/air-quality-clouds.jpg)

When I first think of matter, I think matter is the things that have weight and takes space. The reason that I think air is not a matter it's because air is invisible, it seems that air don't takes space and it doesn't have weight either. After reading some articles about air and matter, I finally understand it and I found out the 3 big categories of matter: gas liquid, solid. Air does take up space, even though we can't see it, and air has weight, even if we can't feel it. I am not lying, this had been observed and analyzed by some scientists.