Chapter 9, Problem 52QP

Interpretation Introduction

Interpretation:

The reason why ${\text{Be}}_{\text{2}}$ molecule does not exist is to be discussed based on the molecular orbital theory.

Concept introduction:

Two atomic orbitals combine to form onebonding and oneantibonding molecular orbitals. Orbitals that lie on internuclear axis combine to form $\sigma$

(sigma) molecular orbitals, and orbitals parallel to each other combine to form $\pi$

molecular orbitals.

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

orbitals are a bonding molecular orbital, designated by ${\sigma }_{1s}$, and an antibonding molecular orbital, designated by ${\sigma }^{\ast }{}_{1s}$. The $\text{2s}$

orbital forms corresponding molecular orbitals.

The molecular orbitals formed by the combination of ${\text{2p}}_{\text{x}}$

orbitals are a bonding molecular orbital, designated by ${\sigma }_{2{\text{p}}_{\text{x}}}$, and an antibonding molecular orbital, designated by ${\sigma }^{\ast }{}_{2{\text{p}}_{\text{x}}}$.

The molecular orbitals formed by combining ${\text{2p}}_{\text{y}}$ and ${\text{2p}}_{\text{z}}$

orbitals are bonding molecular orbitals, designated by ${\text{π}}_{{\text{2p}}_{\text{y}}}$

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

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

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

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

Higher the bond order, more stable is the molecule. Zero bond order indicates molecule is unstable.