Water can exist in three different states of matter: solid, liquid, and gas. The water molecules are the same in each state, but the distance between them changes as water changes state. Space your four molecules evenly on one sheet of paper. Now place the second sheet of paper next to the first sheet, so the long edges of the sheets are touching. Space your four molecules evenly over both sheets of paper. Compare the two models. Does this demonstration show how the distance between water molecules can change? Were the molecules more tightly-packed on one or two sheets of paper? Explain.