The atomic structure and unique properties of water seem to be especially designed for the biosphere.
Structure of Water Molecule and its Properties:
A water molecule consists of two atoms of hydrogen and an atom of oxygen. Two hydrogen atoms share their only electrons with those of an oxygen atom. The shared electrons are attracted more towards the oxygen nuclei which have a greater positive charge. This results in their asymmetrical distribution and oxygen atom gets a slight negative charge while hydrogen atoms a little positive charge.
The molecule acquires a polarity which causes it to form aggregates, a structure which is referred to as the Lattice structure. It is these aggregates which are responsible for the cohesive nature and a number of unusual properties of water.
1. Water has maximum density at 4°C. When it is cooled below 4°C it expands and freezes at 0°C, so that ice is lighter than water.
2. Water has an extraordinary high specific heat. Variations in its temperature require large amounts of heat energy or its withdrawal as compared to other liquids.
3. As the water molecules are bound together by hydrogen bonds much more energy is required to evaporate it as compared to other liquids. Hydrogen bonds have to be broken for evaporation which needs additional energy.
4. Water is characterised by the highest surface tension among all other liquids. This causes an extraordinary amount of water to be retained in the soil due to capillary action.