Water is a special molecule that has a unique set of properties which set it apart from all others. Life on Earth is made possible because of its unique nature. One interesting property is the polarity of water molecule. In this article, I talk about the reasons behind the molecular polarity of water.
What is Polarity?
What do we mean by 'polarity' of water molecule? Polarity is charge inequality on two ends of any molecule. Due to the unequal distribution of electrons in water molecule, one part of the molecule is more negatively charged than the other part. This is caused by the property of 'electronegativity', which can be defined as ability of an element to attract electrons. If the atoms that make up a molecule have different electronegativities, that differ substantially, they attract electrons unequally, causing polarity.
Water: Molecular Structure
To understand what is polarity of water, one needs to understand the molecular structure of water and the arrangement of electrons in it. The polarity of water molecule arises due to its peculiar molecular structure. The molecule is made up of one oxygen atom covalently bonded with two hydrogen atoms. A covalent bond is formed when two atoms share electron pairs with each other to achieve stability.
Oxygen has six electrons in its outermost orbit. Out of these six electrons, one electron each is shared with two hydrogen atoms, which have one electron in the outermost shell. Through covalent bonding, oxygen shares two pairs of electrons with hydrogen atoms to form the water molecule. Besides these two shared pairs of electrons, water has two pairs of unshared electrons that repulse the other two pairs, leading to distortion in its shape.
Why is Water Molecule Polar?
The polarity of water molecule arises due to its greater electronegativity or electron loving nature, than hydrogen. Even though the pairs of electrons are shared with the hydrogen atoms, they are not shared equally as oxygen pulls the electrons more towards itself. This gives rise to a greater negative charge on the side of oxygen atom and a positive charge on the hydrogen atoms. That means, water molecule becomes polar because of the greater ability of oxygen to attract electrons toward itself. This polar nature of water molecule gives rise to an electric dipole moment.