Question

What is the term defined when a bond is formed by a shared pair of electrons, and each bonding atom contributes one electron to the pair.

Answer 1

We have to know that in chemistry, chemical bonds are three types of classification. This classification is based on electron binding in the bond. There are covalent bonds, ionic bonds and coordinate bonds. The covalent bond is nothing but the mutually sharing of electrons between the two atoms in the molecule. The ionic bond is nothing but highly electronegativity pulls the electrons towards itself, least electronegativity atoms lose the electrons in the molecule. The coordinate bond is nothing but the pair of the electrons from one atom to another atom in the molecule. It is mainly seen in coordination chemistry.

Complete answer:
As we know that the covalent bond is important for chemistry. This covalent bond depends on the mutual sharing of electrons between the atoms in the molecules. In that mutual sharing of electrons in the atom, some overlapping of orbitals are also involved. In this overlapping of orbitals, involve the mutual sharing of electrons in the atom. These overlapping are classified as two types are head wise overlapping and sidewise overlapping. There are two types of covalent bonds. There are sigma bonds and pi bonds.
The covalent bond when a bond is formed by a shared pair of electrons, and each bonding atom contributes one electron to the pair.
Because, ionic and coordinate bonds are not able to be formed by a shared pair of electrons, and each bonding atom contributes one electron to the pair.

Note:
We must remember that the electronegativity difference in the bonded atom plays a vital role whether the bond is ionic or covalent or polar covalent bond. The electronegativity difference between the bonded atom is lesser than $1.7$, means it consider as covalent bond. If the electronegativity difference between the bonded atom is equal to $1.7$, means it consider as polar covalent bond. If the electronegativity difference between the bonded atom is greater than $1.7$, it is considered a polar bond.