The most essential molecule after oxygen that helps in sustaining life is water. The Earth's surface consists of over 75% water. You will find H2O in various forms like ice, snow, vapor, dew, rain, etc. Water is present in streams, lakes, rivulets, rivers, seas, and oceans. It is present in the clouds in form of water vapor. Of the 75% water present on our planet, only 2.7% is freshwater that is usable. H2O is very important for all life forms as all the plants and animals contain water.
Structure of Water Molecule
An H2O molecule is made up of one oxygen and two hydrogen atoms. The latter are covalently bonded to the oxygen atom by sharing a pair of electrons. O2 has two unshared electron pairs that makes up a total of 4 electron pairs present around it. Of these, 2 electron pairs are involved in the covalent bond with hydrogen, and the two lone-pair electrons are present on the opposite side of the atom. This imparts a negative charge to oxygen, and makes it 'electronegative'. The two lone-pairs of electrons on the O2 atom forms the H-O-H bond angle at 104.5 degrees. Hence, a water molecule can be said to have angular structure.
Why is Water Polarized?
In a covalent bond, the electrons are shared equally between the two bonding atoms. But this is not the case with a water molecule. The electron pair is strongly attracted by oxygen than hydrogen in this molecule. This pull of the electrons imparts an asymmetrical distribution of charge, which forms a partial negative charge (δ-) and partial positive charge (δ+) in the molecule. The partial charge is known as polarity, and this property helps in easy dissolution of other molecules in water.
Important of Water Polarity
This characteristic helps the water molecules to stick together by a force called cohesion. It also helps them to bind with molecules of other substances through a force called adhesion. You may have observed in your chemistry experiments that water rises up in a tube (capillary action). This is due to its property of adhesion, i.e., attraction between unlike molecules. Therefore, polarity, cohesion, and adhesion is very important for life. For example, transportation of water in an upwards direction in the plants through tiny tubes called 'xylem vessels' showcases the contribution of this property.
In the human body, the polar nature of H2O is very important especially during the digestion process, wherein the water molecules dissolve numerous other compounds.