Which of the following diatomic molecular species has only π bonds according to Molecular Orbital Theory?

Concept:

Molecular Orbital theory - According to the theory, when atoms are combined to form molecules, formations of molecular orbitals takes place.

• No. of molecular orbitals is equal to the no. of atomic orbitals combined to form a molecule.
• Two types of molecular orbital are there in MOT, bonding and anti-bonding molecular orbital.
• Based on the configuration of the molecular orbital we can calculate the type of bonding and bond order present in the molecule.

Explanation:

Step 1: MOT configuration C₂ is:

\(\sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\pi 2p_x^2 = \pi 2p_y^2\)

Step 2: Bond Order in C₂ = 8-4/2 = 2

Bond order in C₂ is two means a double bond is present in C₂.

Step 3: By observing configuration we can state that only degenerated Pi orbitals only participated in bonding having 4 electrons in total. Also, no sigma electron is participating in bonding. Hence no sigma bond is present in C₂.

So, C₂ molecule has 2 π bonds in its structure.

Hence, the correct answer is option 3.

Important Points To find the type of bond present in a diatomic molecule following steps have to be followed-

Step 1: Write down the configuration of the diatomic molecule according to MOT.

Step 2: Calculate the bond order using the formula - bonding electrons - antibonding electrons / 2

Step 3: Observe the MO configuration, and depending upon the type of electrons participating in bonding, give the type of bonding present in the molecule.