Question

How are sigma bonds counted?

Answer 1

The sigma bonds are formed by the end to end overlap of two orbitals. A single covalent bond is formed by sharing one electron each by the atoms present in the molecule which contain one sigma bond.

Complete answer:
The chemical bonding is the formation of chemical bonds between the two atoms which forms a chemical compound or molecule The chemical bonds keep the atom together and intact in a structure so that the atoms cannot move.
There are many types of bonds formed like ionic bond, covalent bond, hydrogen bond.
Covalent bonds are defined as the chemical bonds which are formed by the mutual sharing of electrons between the two atoms present in the molecule. The covalent bonding is of mainly two types:
1. Covalent $\sigma$ bond: The covalent sigma bond is formed by the end to end overlap of two orbitals which can be two s-orbital, two p-orbital or one s or one p orbital.
2. Covalent $\pi$-bond: The covalent pi bond is formed by the side to side overlap of the p-orbitals parallel to each other.
The single covalent bond is formed between the atoms, when only one pair of electrons is shared between the atoms. A single bond between the atom contains only one covalent $\sigma$ bond.
The double covalent bond is formed between the atoms, when two pairs of electrons are shared between the atoms. A double bond between the atoms contains only one covalent $\sigma$ bond and one $\pi$-bond.
The triple covalent bond is formed between the atoms, when three pairs of electrons are shared between the atoms. A triple bond between the atoms contains one covalent $\sigma$ bond and two $\pi$-bond.

Note:
You must know that the covalent sigma bond is much stronger than the covalent pi bond because in sigma bond orbitals are along the internuclear axis which results in more effective overlap as compared to pi bonds.