Question

The bond order depends on the number of electrons in the bonding and antibonding orbitals. Which of the following statements is/are correct about bond order?
(a) Bond order cannot have a negative value
(b) It always has an integral value
(c) It is a non-zero quantity
(d) It can assume any value – positive, integral or fractional, including zero

Answer 1

According to Lewis theory, bond is the number of electrons which hold the two different or same atoms together, and by molecular orbital theory, it is one-half of the difference between the bonding orbital, and antibonding orbital.

Complete step by step answer:
Bond order is given by the formula:
Bond order = $\dfrac{1}{2}$ (Number of electrons in bonding orbital - Number of electrons in antibonding orbital)
When electrons of two atoms which are taking part in bond formation are present in between the nuclei of those atoms then these electrons are placed in bonding orbitals, and when electrons of two atoms which are taking part in bond formation are present outside the nuclei of those atoms then these electrons are placed in antibonding orbitals.
(1) For option (a), it is a true statement because by the definition of bond order, it tells how many bonds there are in a molecule, so it is not possible to have a negative number of bonds. Hence, it is an incorrect answer.
(2) For option (b), bond order is one-half of the difference between the bonding orbital, and antibonding orbital. When this difference comes out to be an odd number, the bond order is no longer an integral value. Hence, this option is incorrect.
(3) For option (c), the difference between the bonding orbital, and antibonding orbital is zero when there are equal numbers of electrons in bonding, and antibonding orbitals. So, the overall result of the bond order comes out to be zero. Hence, it cannot be a non-zero quantity always.
(4) For option (d), it can be observed from the above three points that bond order can have any value either positive, integral, fraction or zero.
Thus, the correct answer is option D.

Note:
Rules to fill electrons in the molecular orbitals: Filling of electrons should be started with the lowest energy orbital according to the Aufbau principle with a maximum of two electrons in an orbital with opposite spins according to the Pauli Exclusion principle.