Question

According to MO theory, which molecule or ion has the highest bond order? Highest bond energy? Shortest bond length?

Answer 1

Concepts and reason

Molecular orbital theory:

During the bond formation the atomic orbitals of individual atom will combine together to form equal number of molecular orbital. These orbitals are arranged in the order of increasing energy level, while in case of valence bond theory, the individual atomic orbital will directly involve in bond formation.

Bond order:

Bond order of the molecule indicates the number of bonds present between the pair of atoms.

Bond order is the measurement of the bond strength of a molecule.

An increase in the bond order shows the increase in the bond strength and therefore, a stable compound is formed.

Bond order can be calculated by using molecular orbital theory and molecular energy diagram.

Bond energy is defined as the amount of energy required to break all the bonds in one mole of a substance.

Bond length: The average distance between the two bonded atoms, Bond length is inversely proportional to the bond order.

Fundamentals

Molecular orbitals:

Linear combinations of atomic orbitals are called molecular orbitals. These molecular orbitals are generally divided into two types:

(i)Bonding orbitals

(ii)Antibonding orbitals

Bond order in terms of molecular orbitals:

If the bond order is high, then the atoms are close to each order, then distance between the atom will be short and bond energy will be high.

General molecular orbital diagram: Valence shell electrons only

(a)

Molecular orbital diagram of molecule was given below, total of electrons in

Molecular orbital diagram of molecule was given below, There total of electrons in

Molecular orbital diagram of molecule was given below,

Total number of electrons in is

Bond order of the given molecules , ,

Since molecule have highest bond order it will have the highest bond energy and shortest bond distance.

(b)

The given molecule here is , the total number of electrons in is 14, molecular orbital diagram for this molecule was given below

The given molecule here is , the total number of electrons in is , molecular orbital diagram for this molecule was given below

Bond order of the given molecules and

The bond order of and was calculated as and , Therefore it was identified that is the molecule with highest bond order and hence it posses the shortest bond distance and highest bond energy.

Ans:

Among the given set of molecules , and , the molecule with highest bond order is , so it posses the shortest bond distance and highest bond energy.

Among and , the molecule with highest bond order, shortest bond distance and highest bond energy is .