Why is Water a Polar Molecule

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 water in various forms like ice, snow, vapor, dew, rain, etc. Water is present in streams, lakes, rivulets, rivers, sea and ocean. It is present in the clouds in form of water vapor. Of the 75% water present on earth, only 2.7% water is freshwater that is usable. Water is very important for all life forms as all plants, animals and human body contains water. In this article, we will learn about why is water a polar molecule and why is polarity important. But before we move on to the hard-core basics, let's know more about structure of water molecule.

Structure of Water Molecule
The structure of water molecule is very simple. A water molecule is made up of one oxygen atom and two hydrogen atoms. The hydrogen atoms are covalently bonded to the oxygen atom by sharing a pair of electrons. The oxygen atom has two unshared electron pairs that makes a total of 4 electron pairs present around the oxygen atom.

Of these 4 electron pairs of oxygen, 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 oxygen atom. This gives oxygen a negative charge and makes it an 'electronegative' atom. In other words, it is an 'electron-loving' atom. The two lone-pairs of electrons on the oxygen atom make the H-O-H bond angle at 104.5 º. This angel is slightly less than the 109 º28' of the tetrahedral angle. This makes the structure of water molecule an angular structure.

Why is Water Polarized?
As explained above, water molecule is formed by two hydrogen atoms that are covalently bonded with an oxygen atom. In a covalent bond, the electrons are shared equally between the two bonding atoms. But this is not the case with water molecule. In the water molecule, the electron pair is strongly attracted by oxygen than hydrogen. This pull of the electrons by oxygen atom gives an asymmetrical distribution of charge. This asymmetry leaves the molecules with a partial negative charge (δ^-) and partial positive charge (δ⁺). This partial charge of molecules is known as polarity. This property of polarity helps other molecules to dissolve easily in water.

Why is Water Polarity Important?
Many students have a question, why is polarity important in water. The property of polarity helps the water molecules to stick together by a force called cohesion. Polarity also helps water molecules 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, that is called capillary action. This is due to its property of adhesion, that is, attraction between unlike molecules. Therefore, polarity, cohesion and adhesion is very important for life. Water can not only bind to water molecules, but also other molecules that helps in transportation of water up in the trees through tiny tubes called the 'xylem vessels'. This makes water polarity important for living things.

The hydrogen bonds are not as strong as covalent bonds. But these bonds are strong enough to bind water molecules together. You should always keep in mind the two most important characteristics of water. The first characteristic due to polarity is the ability to dissolve any substance and the next characteristic is the low density of water in its frozen state.