That the motion of water molecules in each state of matter is similar to what happens for most substances. Adding energy increases the motion of the molecules and causes them to move further apart. Removing energy decreases the motion of the molecules and causes them to move closer together. But, water does something very unusual when it freezes to become ice. The molecules, which were moving closer and closer together, move further apart as they organize themselves into the open ring pattern shown below for ice. This is why ice expands when it freezes.