Question

If the intermolecular axis is taken to be in z- direction, then molecular orbitals obtained from $2{p_x}$ and $2{p_y}$ orbitals are not symmetrical around the bond axis.
A. Positive lobes are above the molecular plane and negative lobes are below the molecular plane
B. Negative lobes are above the plane and positive lobes are below the plane
C. Positive and negative lobes both are in the same plane
D. All of the above

Answer 1

Hint: To answer this question, you must recall the shapes and arrangement of the orbitals in molecules. The p orbital is dumbbell shaped with a node at the middle. The p orbitals are present along axes that they denote.

Complete step by step solution:
- In the question, we are given that the intermolecular axis lies along the z- axis. So in bond formation, the atomic orbitals of an atom are mixed in such a manner so as to produce equivalent orbitals. One of the lobes of the dumbbell shaped p orbitals is positive and one is negative.
- In the atomic orbitals, the positive lobes lie above the plane and negative lobes lie below the plane.
- Now the orbitals combine in two ways making either a bonding molecular orbital (when the positive lobe combines with the positive lobe and the negative lobe combines with the negative lobe) or an antibonding molecular orbital (when the positive lobe of one atomic orbital combines with the negative lobe of the other orbital).
- As a result, in the bonding molecular orbitals the positive lobes lie above the plane and negative lobes below the intermolecular axis. In the antibonding molecular orbitals the positive and negative lobes lie both above the intermolecular axis and below the axis. Or in other words, they lie in the same plane.
The molecular orbitals formed by the $2{p_x}$ and $2{p_y}$ orbitals lie in the opposite x-y plane.

Thus, the correct answer is A.

Note: The p orbitals have two lobes on either side of the plane passing through the nucleus having probability of finding the electron as zero on it. There are 3 p orbitals and all three of them have the same shape and energy and lie on the x- axis, y- axis and z axis respectively.