Question

Draw the MO energy level diagrams for N₂, N₂⁺, and N₂^- Calculate the bond order for each. Which has the shortest bond? Which is/are paramagnetic?

Draw the MO energy level diagram for O₂^- and calculate its bond order.

Answer 1

Concepts and reason

The concepts used in this problem is molecular orbital theory.

Fundamentals

Bond order:

It is the number of chemical bonds between two atoms and calculated by the following formula.

Bond order =

Bond length:

Bond length is the distance between two covalently bonded atoms.

(a)

The electronic configuration of ${{\rm{N}}_2}$ $\left( {14} \right)$ is:

The electronic configuration of ${{\rm{N}}_2}^ +$ $\left( {13} \right)$ is:

The electronic configuration of ${{\rm{N}}_2}^ -$ $\left( {15} \right)$ is:

The molecular orbital diagram of ${{\rm{N}}_{\rm{2}}}$ , ${{\rm{N}}_2}^ +$ ^, and ${{\rm{N}}_2}^ -$ are:

${{\rm{N}}_{\rm{2}}}$	${{\rm{N}}_2}^ +$	${{\rm{N}}_2}^ -$
Bond order = = $= 3$	Bond order = = $= 2.5$	Bond order = = $= 2.5$
Since the bond order of N2 is highest among all, so, the bond length of ${{\bf{N}}_{\bf{2}}}$ is shorter than ${{\rm{N}}_2}^ +$ , and ${{\rm{N}}_2}^ -$ .
Diamagnetic	Paramagnetic	Paramagnetic

(b)

The electronic configuration of ${{\rm{O}}_2}^ -$ is:

The molecular orbital diagram of ${{\rm{O}}_2}^ -$ is as follows:

Bond order =

=

$= 1.5$

Therefore, the bond order of ${{\rm{O}}_2}^ -$ is $1.5$ .

Ans: Part a

Hence, ${{\bf{N}}_{\bf{2}}}$ have the shortest bond.

Part b

The bond order of O₂^- is ${\bf{1}}.{\bf{5}}$ .