The properties
of water

Like all matter, water is made up of atoms. Atoms attach together, or bond, to form molecules. Two hydrogen atoms bonded to an oxygen atom form a water molecule. Water has several properties that make it a very unique substance.

Polarity
When electrons are not shared equally in a covalent bond, the molecule is described as polar. Water molecules are ploar. This means that while water molecules are neutral as a whole, one end of the water molecule tends to have a positive charge while the other has a negative charge. The oxygen end has a slight negative charge while the hydrogen end has a slight positive charge. Each end of a water molecule is attracted to the opposite charged end of another water molecule. Water's polarity is responsible for the "stickiness" or cohesion between the molecules.

Capillary Action
Cohesion of water causes capillary attraction, which is the ability of water to move upward in small spaces. Cohesion makes it possible for water to move up the fibers of a plant. This is how plants get the water they need to survive. In addition, it moves water upwards in soil. Cohesion of water also causes surface tension, water's invisible skin which allows water striders to walk on water

Surface Tension
Water is considered the "universal solvent" because its bipolar molecule enables it to dissolve a wide variety of substances. Solubility is affected by polarity. Polar substances can dissolve other polar substances. Non-polar substances dissolve other non-polar substances. Polar substances and non-polar substances, however, do not mix.

Density
Another property of water is density during phase changes. The density of most substances increases when a liquid becomes a solid. Solid water is actually less dense than liquid water. It is for this reason that ice floats. Can you imagine a world where ice sank? Lakes would freeze from the bottom up, killing many fish. Frozen water in the polar regions would sink and change the ocean levels. The fact that ice floats is essential for the survival of many aquatic ecosystems and ultimately life on Earth.