Chapter 9, Problem 95AP

Interpretation Introduction

Interpretation:

The difference in bond enthalpies of ${\text{F}}_{\text{2}}$

and ${\text{F}}_{\text{2}}{}^{-}$

is to be determined using the molecular orbital theory.

Concept introduction:

According to the molecular orbital theory:

Two atomic orbitals undergo a combination process in order to form a bonding and an antibonding molecular orbital. Orbitals that lie on internuclear axis combine to form sigma $\sigma$ molecular orbital, and orbitals parallel to each other combine to form $\pi$

molecular orbitals.

The molecular orbital formed by the combination of $\text{1s}$

orbital forms bonding molecular orbital designated as ${\sigma }_{1s}$ and antibonding molecular orbital ${\sigma }^{\ast }{}_{1s}$. The $\text{2s}$ orbital forms corresponding molecular orbitals.

Molecular orbital formed by the combination of ${\text{2p}}_{\text{x}}$ orbital forms a bonding molecular orbital designated as ${\sigma }_{2{\text{p}}_{\text{x}}}$

and an antibonding molecular orbital designated as ${\sigma }^{\ast }{}_{2{\text{p}}_{\text{x}}}$.

Molecular orbitals formed by combining ${\text{2p}}_{\text{y}}$ and ${\text{2p}}_{\text{z}}$ orbital forms bonding molecular orbitals designated as ${\text{π}}_{{\text{2p}}_{\text{y}}}$

and ${\text{π}}_{{\text{2p}}_{\text{z}}}$, and antibonding molecular orbitals designated as ${\text{π}}^{\ast }{}_{{\text{2p}}_{\text{y}}}$

and ${\text{π}}^{\ast }{}_{{\text{2p}}_{\text{z}}}$.

Electrons are filled in the molecular orbitals in increasing order of their energy.

Bond order is determined by subtracting the number of electrons in antibonding orbitals from the number of electrons in bonding, divided by two.

The higher the bond order, the more stable is the molecule and thus higher is the bond enthalpy.