The chemical compounds that are held together by polar covalent bonds are known as polar compounds. The word 'polar compound' can be defined as a chemical species consisting of two or more atoms that are kept together due to the unequal sharing of electrons by covalent bonds that are polar in nature. The differences in the electronegativities of the bonded atoms may cause the bond pair of electrons to move closer to the more electronegative atom when two atoms are bound together by a covalent bond.
Overview of Polar Compounds
It is important to remember that polar compounds are different from ionic compounds. Ionic compounds are held together by ionic bonds that occur between ions due to electrostatic forces. In such situations, to form a cation, one of the atoms loses an electron and another atom receives an electron to form an anion. In polar compounds, there are two chemical species sharing the electron pair. However, due to the variations in electronegativity of the two chemically bound species, the electron pair is exchanged in an unequal way.
No compound is a hundred percent ionic nor covalent. Even when the two hydrogen atoms combine by covalent bond, they possess some ionic character.
Heteronuclear molecules are said to be polar compounds because the electron pair sift towards the more electronegative atom resulting in the polarity of bonds. Due to this polarity, the molecule possesses the dipole moment. The dipole moment is defined as the product of the magnitude of charge and distance of separation of charges. It is denoted by ‘d.’ The dipole moment is expressed in Debye.
μ = q x d
Examples of Polar Molecule
Here are some examples of polar compounds-
Water is a polar compound since the water molecule's covalent bonds between hydrogen and oxygen are polar in nature. Owing to the variations in the electronegativity of hydrogen and oxygen, the bond polarity of the hydrogen-oxygen bond occurs. It draws the bond pair of electrons closer to itself, as oxygen is more electronegative than hydrogen. This allows a partial negative charge to be produced by the oxygen atom and a partial positive charge to be developed by the hydrogen atom.
As the covalent bond between hydrogen and fluorine in this compound has a polar nature, hydrogen fluoride is a polar compound. Since fluorine is much more electronegative than hydrogen, it draws the electron bond pair closer to itself and, in the process produces a partial negative charge. The hydrogen atom, on the other hand, produces a partial positive charge (since the bond pair of electrons is placed quite far away from the nucleus of the hydrogen atom).
A polar covalent bond between the terminal carbon and the hydroxyl group occurs in the ethanol molecule. As oxygen is more electronegative than carbon, this carbon-oxygen bond is polar in nature, allowing it to move the bond pair of electrons closer to itself and gain a partial negative charge in the process. Since the electron pair is located relatively far away from its nucleus, the carbon atom gains a partial positive charge.
Differentiation of Polar Compounds from the Non-Polar compounds
Let us look at the differentiation of the polar compounds from the non-polar ones.
Polar compounds have atoms with differing electronegativity, which is usually quite large. As a result, the atom that is more electronegative than the other tends to draw the linked electron (in a covalent bond) toward itself. This results in a loss on more electronegative ones and addition on less electronegative ones with less charges.
The electronegativity of an atom is related to its diameter. Because the nucleus is further away from the outer valence electron shell or bonded electrons, the larger the diameter, the less electronegative it gets. This also explains why group 7 tends to undergo more ionic reactions than covalent reactions (larger diameter loss easily than holding on).
Because the atoms in non-polar are of relatively identical size/diameter, their electronegativity is more or less equal, bound electrons sit between them (equal distance apart).
Non-polar chemicals are soluble in non-polar compounds, such as butane in octane/gasoline, and polar compounds are soluble in polar compounds, such as ethanol in water.
Did You Know?
There are two important factors to determine the polarity of bonds-
To determine the polarity of bonds, check the electronegativity of an atom. If the difference between electronegativities is less than or equal to 0.4 then the compound is said to be non-polar and if the difference between electronegativities lies between 0.5 to 1.7 the compound is said to be polar.
Molecules with bent and trigonal pyramidal shapes are always polar.