Question

Pure covalent bond is present in:
A) ${\text{H}} - {\text{Cl}}$
B) ${\text{Cl}} - {\text{Cl}}$
C) ${\text{C}} - {\text{Cl}}$
D) ${\text{Na}} - {\text{Cl}}$

Answer 1

To solve this we must know that a pure covalent bond is formed between two atoms that have same electronegativities. Also, the atomic size of the bonding atoms should be the same. We must now the atoms whose electronegativities are the same.

Complete step-by-step answer:
We know that a pure covalent bond is formed between two atoms that have the same electronegativities. Also, the atomic size of the bonding atoms should be the same.
A pure covalent bond is formed by an equal sharing of electrons from both the atoms that are bonded. The electron pair involved in covalent bonding is known as a shared pair or bonding pair. A pure covalent bond has no ionic character.
The covalent bond is also known as molecular bond. The atoms achieve stability due to the sharing of bonding pairs. Diatomic molecules generally have covalent bonds.
We are given four bond between ${\text{H}} - {\text{Cl}}$, ${\text{Cl}} - {\text{Cl}}$, ${\text{C}} - {\text{Cl}}$ and ${\text{Na}} - {\text{Cl}}$.
Consider the bond between chlorine and chlorine atom ${\text{Cl}} - {\text{Cl}}$. The electronegativity and the size of both the bonded atoms are the same.
Thus, pure polar covalent bond is present in ${\text{Cl}} - {\text{Cl}}$.

Thus, the correct option is (B) ${\text{Cl}} - {\text{Cl}}$.

Note: The bond between ${\text{H}} - {\text{Cl}}$ is a polar covalent bond as the electronegativity difference is zero. The bond between ${\text{C}} - {\text{Cl}}$ is a slightly polar bond as the electronegativity difference is very low. The bond between ${\text{Na}} - {\text{Cl}}$ is an ionic bond as the electronegativity difference between sodium and chloride ions is very high. As a result the bond loses its covalent nature and becomes ionic.