Question

Two atoms are bonding along the Z-axis. How will the \( \pi^* \) orbital look like (Z is the internuclear axis)? 

• A. A
• B. B
• C. C
• D. D

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to identify the visual representation of an antibonding pi molecular orbital (\(\pi^{*}\)) formed when the internuclear axis is the Z-axis.
Step 2: Detailed Explanation:
A \(\pi\) bond is formed by the sideways (lateral) overlap of atomic p-orbitals. When the internuclear axis is the Z-axis, \(\pi\) bonds are formed by the overlap of \(p_{x}\) or \(p_{y}\) orbitals.

A \(\pi^{*}\) (antibonding) molecular orbital is formed when these p-orbitals overlap in out-of-phase (destructive interference). This means the wavefunctions of the overlapping lobes have opposite signs.

Characteristics of a \(\pi^{*}\) orbital:
1. There is a nodal plane between the two nuclei (perpendicular to the internuclear axis).
2. There is another nodal plane containing the internuclear axis.
3. The overlapping lobes facing each other laterally have opposite signs (+ and -).

Looking at the diagrams:
- Diagram 1 shows lobes of same signs facing each other; this represents a \(\pi\) (bonding) orbital.
- Diagram 2 shows end-to-end overlap, representing sigma (\(\sigma\)) bonding/antibonding.
- Diagram 3 shows sideways overlap where a positive lobe of one atom faces a negative lobe of the other. This accurately represents the \(\pi^{*}\) orbital.
Step 3: Final Answer:
The correct representation of the \(\pi^{*}\) orbital is given in diagram 3, which is Option (C).