article rewrite hi i am currently re writing this article so it makes more sense and is more wikified i am doing this as a step process while i complete this please leave comments on this page until i'm done thanks step definition complete step characteristics complete step macroscopic properties complete step microscopic properties needs expansion its currently stub like step gas models complete step special topics needs expansion its currently stub like step history complete step references complete step clean up complete step review this is for other wikipedians to do