Скачать или смотреть Why ice floats on liquid water? Why volume of water increases on freezing?

Water molecules forms a special hydrogen bond where hydrogen atom is shared unequally. At temperatures above 4 degree C, since water molecules have high kinetic energy, they keep on randomly moving and this hydrogen bond forms and breaks.
But at temperatures below 4 degree C, the kinetic energy of water molecules decrease and they no longer move away from each other fast and the hydrogen bonds between water molecules does not break frequently, generating a structure which we know as ice cubes that is less dense than the liquid water.
So the water molecules are denser at temperatures above 4 degree C but below 4 degree C, the water molecules becomes less dense as they form a structure and as we know less dense material float on high density liquid so ice cubes float on liquid water. Also since the generation of a structure causes some space between the water molecules the volume of the water also increases when it freezes and hence it breaks the glass bottle if it is completely filled.

Chapters:
0:00 Example from daily life
0:40 Chemical structure of water
1:53 Bonds in water molecule
2:06 Explanation
3:24 Conclusion