Important Properties of Water

Water, in the form of H2O is probably the most important substances for all living organism on this planet due to its unique properties. To understand these properties, we must first understand some important terms in order to understand the following concepts.

Electronegativity - Assigned to each element, this represents the force of attraction an atom has to electrons. The larger the electronegativity number, the stronger the atom attracts the electrons of a covalent bond. Covalent bonds that have unequal sharing of electrons are said to be polar, and those evenly shared are non-polar. (only happens in covalent bonds)

van der Waals forces - these forces include London dispersion forces,dipole-dipole attractions, and hydrogen bonds. These forces are caused by the unequal sharing of electrons resulting in intermolecular bonds. These forces keeps molecules together in certain substances.

Universal Solvent

     Due to the reason that water is highly polar molecule, it has the ability to dissolve almost all polar materials. This is the most important reason why most organisms are mainly composed of water, its because water's ability to dissolve body's important materials and nutrients.

Cohesion 
    Water molecules have a special ability to attract one another. This is caused by the polar covalent bonding in the water molecule. The electrons shared in the water molecules stays relatively longer around the oxygen atom, and shorter around the hydrogen atoms, this is caused by oxygen's greater electronegativity. The oxygen is said to be electronegative, and the hydrogen atoms are electropositive. therefore, the oxygen of one water molecule attracts the hydrogen atom of a nearby molecule, forming an hydrogen bond.
This also results in a high surface tension in water, due to its cohesive force, many organisms can stay on the surface of water.

                                                           Adhesion
   Water can also "stick" to other polar materials by forming hydrogen bonds with them. An good example of this would be capillary action, where climbs up a narrow tube on its own. 



High Heat Capacity
      Water molecules have the ability to absorb large amounts of heat energy before its temperature would raise appreciably. Similarly, it also must lose a significant amount of heat before the temperature decreases. This ability allows organisms to keep a constant body temperature.

Density
     Water is most dense at 4 degrees Celsius, below/above 4 degrees, the hydrogen bonds between the V-shaped molecules spread the molecules apart, reducing its density. This property allows ice to float on water in the winter, also acting as an insulator, allowing aquatic organisms to live through winter.