Here is a site that has some of these explanations. If you look over to the right, there is a list that includes topics like "States" and "Phase change". Start with the "Matter" page and then go straight down the list.
I know that Isaac Asimov wrote a couple of great, very conversational science essays about water and ice that discussed the physical structural changes that happen during phase changes in water specifically. I read them when I was about 7 or 8. If you can get your hands on some of his books of collected science essays, you might find what you are looking for there.
Edit: I believe that the essay might be in "The Left Hand of the Electron".
