Polarity of Water
Water (H2O) is a neutral molecule consisting of two atoms of hydrogen (H) and one atom of oxygen (O). The highly electronegative oxygen atom is bonded to each hydrogen atom through single covalent bonds. Because oxygen is more electronegative than hydrogen, it attracts the bonding electron pairs and acquires a partial negative charge. On the other hand, the two hydrogen atoms acquire partial positive charges. The difference in electronegativities between O and H results in dipole moments [1-5].
Lewis dot structure of water shows that oxygen has two lone (nonbonding) pairs of electrons. These electron pairs exert repulsive forces on the bonding electrons, pushing the bonds inward and resulting in a non-linear shape of the water molecule. Water has a bent or V shape with a bond angle of 104.5o . The two dipole moments due to O-H bonds do not cancel, resulting in a net dipole moment. Therefore, the water molecule is polar.
As a result of polarity, water molecules attract each other and form hydrogen bonding. Moreover, water confined to a container exhibits surface tension. Water attracts other polar molecules like sugar, amino acids, and nucleic acid. It can dissolve many ionic and polar covalent compounds. Therefore, its polarity influences its properties as a solvent. It is for this reason that water polarity is important.
A molecule that bonds with a water molecule is called hydrophilic. On the other hand, non-polar substances such as oil do not mix with water. A molecule that is not attracted to water molecule is called hydrophobic.