Thanks, wwh. That's a good beginning.

Now under the microscope--how are they different?

I learned something interesting the other night--I learned that all oxygens are not created equally. A geologist trying to determine whether the moon was ever part of the earth examined moon rocks and found that the oxygen contained in the rocks was the same as the oxygen in our own rocks. This realization upset a physicist who had hoped that the moon came to us from another source. I read that the oxygen on Mars rocks, for instance, is different in structure from our own oxygen.

Anyway, all of that has led me to wondering how frost and ice are different. And it is especially interesting to consider how water vapor and water are different, other than the obvious point about their being in different states, one gaseous and the other liquid.