Each water molecule consists of one oxygen atom and two hydrogen atoms. The oxygen atom bears a slight electronegative charge while hydrogen possesses a more positive one. Because opposite charges attract, the water molecules are drawn together. When an oxygen atom is linked to a neighboring molecule's hydrogen atom, a bond called a hydrogen bond is formed. In an ice crystal the hydrogen bonds govern the shape of the crystal so that the grid of molecules surrounds relatively large spaces. In a liquid form, water has no such spaces; thus ice is less dense and will float on liquid water. If not for this, great bodies of water would freeze from the bottom up without the insulation of a top layer of ice and all life in the water would die. The water molecule is a very small one but because of its unique properties it behaves like a larger one. The bonds between water molecules are so strong that water resists changes in its state (Solid, liquid, gas); thus water has a higher melting point and a higher boiling point than another molecule of similar size. If water followed the example of other molecules its size it would have a boiling point of -75 degrees C and a freezing point of -125 degrees C4. This would mean that, on Earth, water would be a gas all of the time and life would not be possible.
When heat is applied to solid water, some hydrogen bonds get so much kinetic energy that they break and the ice melts. Liquid water does not necessarily have all four hydrogen bonds present at all times but it must retain some of them. For any object to penetrate water, it must be able to break the hydrogen bonds on the surface of the water. These bonds resist breaking thus forming a