Covalent bonds or molecular bonds are the chemical bonds involving the sharing of electron pairs between two or more atoms. These electron pairs are also known to be shared pairs or the bonding pairs, the stable balance of attraction and repulsion forces between the atoms when they are sharing electrons is known as the covalent bonding. For a lot of molecules, with correspondence to the stable electronic configuration, the sharing of the electrons helps each of the atoms in attaining a full outer shell.
The term “covalent bond” was first used in 1939 even though in 1919, Irving Langmuir had introduced the term “covalence” for describing the number of electron pairs that were shared with the neighbouring atoms.
Covalent bonding includes a lot of variety of interactions like the metal-to-metal bonding, agnostic interactions, the bent bonds, the three-center two-electron bonds, the σ-bonding and also the Π-bonding.
Covalency is greatest when it is between the atoms of similar electro negativities. Hence, the covalent bonding does not mean that there has to be two atoms of same elements but only that they should have comparable electro negativity. When the covalent bonding occurs between more than two atoms (i.e. sharing of electrons that occurs between more than two atoms) then it is known to be delocalized.
The Octet rule states that all the atoms in a molecule should have 8 valence electrons in their outer shell – either by means of sharing, losing or gaining electrons- to gain stability. In Covalent bonding, atoms share their electrons with each other for satisfying the Octet rule. Each of the electron needs to become stable by filling up their outer shell in order to attain the charge of 0.
The exception to the octet rule are Hydrogen (H) and Helium (He) since they follow the duet rule. They just have one orbit and can contain only 2 electrons.
UNDERSTANDING THE COVALENT BONDING
Imagine two scenarios:
- X1 is an atom which has one extra electron in its outer shell and X2 is an electron with one less electron i.e. has only seven electrons in its outer shell. Instead of trying to gain 7 electrons for becoming stable, X1 would easily donate its 1 electron to X2 and both would become stable. This donation of electrons can be termed as ionic bonding.
Eg. In the case of Sodium (Na), it has only one electron in its outer shell. And Chlorine (Cl) has seven electrons in its outer shell. Then, Na donates one electron to Chlorine and becomes Sodium Chloride with Na acquiring a positive charge and Cl acquiring a negative charge.
- Both X3 and X4 are electronegative in nature. Both are not ready to lose their electrons, so they tend to share the valence electrons with each other. This sharing is known as covalent bonding.
Eg. Chlorine has 7 electrons in its outer shell. So both the Chlorine atoms share one electron with each other becoming Cl-Cl.
POLAR AND NON POLAR COVALENT BONDING
- Polar covalent bonding occurs when electrons are shared equally between the atoms. It often occurs between same atoms. Eg. Cl-Cl
- Non polar covalent bonding occurs between two different type of atoms and the electrons are not shared equally between the atoms. Eg. H-Cl