A type of chemical bond formed by sharing electrons between two or more atoms is called a covalent bond. Covalent bonds are formed between two similar elements, whether metal or non-metal or between non-metals. An electron from the outermost shell of an atom cannot be exchanged between two atoms with less difference in electronegativity. The outermost orbital of these elements are filled and require just one or two electrons to fill the octet and form covalent bonds.
Let’s take an example of a chlorine molecule Cl2:-
In the formation of Cl2 molecules, the two chlorine atoms share electrons among themselves, where each atom contributes one electron to the shared pair. The electronic configuration of the chlorine atom is [Ne]3s2 3p5, which has one electron short of the argon configuration.
There are three types of covalent bonds based on the number of bonds formed or electrons shared between two or more elements :-
In a single covalent bond, one pair (2 electrons) takes part in forming a bond. This bond is formed to complete the octet and attain a stable electronic configuration. Non-metals or non-metals and metalloids led to the formation of a double bond.
Some of the features of single bonds are the large bond length and weak bond strength. This feature makes them less reactive and hence highly stable. A single dash line [-] represents a single bond.
In a double covalent bond 2 pairs (4 electrons) take part in forming a bond. The bond is formed to complete the valence electron and become stable. Non-metals or non-metals and metalloids led to the formation of a double bond.
Double covalent bonds are unstable due to their long bond length and high bond strength despite their moderate reactivity. The double dash ( = ) graphically represents them.
In a triple covalent bond 3 pairs (6 electrons) take part in forming a bond. The bond is formed to complete the octet and become stable. Non-metals, non-metals, and metalloids lead to forming a triple bond.
As a result of triple covalent bonding, the bond length is short and has high bond strength. Due to their high reactivity, triple dashes ( ≡ ) represent triple covalent bonds.
Covalent bonds are classified into two types based on polarity
The bond formed between two non-metallic atoms with an electronegativity difference between 0.4 and 1.7 leads to polar covalent bonds.
For example, in a water molecule, two polar covalent bonds are formed between oxygen and hydrogen. The electrons of the hydrogens in the water molecule H2O stay closer to the electronegative oxygen longer than in the water molecule H2O.
The bond formed between atoms with equal electronegativity and the atoms with an electronegativity difference of less than 0.4 leads to forming a non-polar Covalent Bond. Equal electron distribution shares between the atoms in non-polar covalent bonds.
For example- In the case of Chlorine molecule Cl2, the electron pairs that are created between two chlorine atoms of equal electronegativity form a non-polar covalent bond.
In covalent bonds, more than one electron pair may be shared between atoms if a single electron pair is not enough to satisfy the valence of an atom. Some important properties of covalent bonds are as follows:
In heavy metal adsorption, covalent bonding is induced by polarization, and electrostatic forces and covalent bonding forces work together. Quantitative separation is possible between these forces. Covalent bonding energy induced by polarization is less than that of a classical one. Control and adjustment are possible in covalent bonding energy.
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