Polar vs Nonpolar Covalent Bonds
As proposed by the American chemist G.N.Lewis, atoms are stable when they contain eight electrons in their valence shell. Most of the atoms have less than eight electrons in their valence shells (except the noble gases in the group 18 of the periodic table); therefore, they are not stable. These atoms tend to react with each other, to become stable. Thus, each atom can achieve a noble gas electronic configuration. Covalent bonds are a major type of chemical bonds, which connect atoms in a chemical compound. There are two types of covalent bonds as non-polar and polar covalent bonds.
What is Polar Covalent Bond?
Polarity arises due to the differences in electronegativity. Electronegativity gives a measurement of an atom to attract electrons in a bond. Usually Pauling scale is used to indicate the electronegativity values. If the electronegativity difference between the two atoms is very large (more than 1.7), then the bond will be ionic. For a bond to be a polar covalent bond, the electronegativity difference should not exceed the value 1.7. Depending on the degree of electronegativity difference, the covalent character can be changed. This degree of difference may be higher or lower. Therefore, the bond electron pair is pulled more by one atom compared to the other atom, which is participating in making the bond. This will result in an unequal distribution of electrons between the two atoms, and these types of covalent bonds are known as polar covalent bonds. Because of the uneven sharing of electrons, one atom will have a slightly negative charge whereas the other atom will have a slightly positive charge. At this instance, we say that the atoms have obtained a partial negative or positive charge. The atom with a higher electronegativity gets the slight negative charge, and the atom with a lower electronegativity will get the slight positive charge. Polarity means the separation of the charges. These molecules have a dipole moment. Dipole moment measures the polarity of a bond, and it is commonly measured in debyes (it also has a direction).
What is Non-Polar Covalent Bond?
When two of the same atom or atoms having the same electronegativity form a bond between them, those atoms pull the electron pair in a similar way. Therefore, they tend to share the electrons, and this kind of bonds is known as non-polar covalent bonds. For example, when the same atoms are joined to form molecules like Cl2, H2, or P4, each atom is bonded to another by a non-polar covalent bond.
What is the difference between Polar Covalent and Non-Polar Covalent Bonds?
• Covalent bonds, which are non-polar, are made by two atoms with similar electronegativities. Polar covalent bonds are made by two atoms with different electronegativities (but the different should not be exceeding 1.7).
• In non-polar covalent bonds, electrons are equally shared by the two atoms participating in making the bond. In polar covalent, electron pair is pulled more by one atom compared to the other atom. So the electron sharing is not equal.
• In polar covalent bond, the atoms have partial positive and negative charges, but in non-polar bonds, there are no partial charges for the atoms.
• Polar covalent bond has a dipole moment, whereas a non-polar covalent bond does not.