Question

Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?

• A. 1s and 1s
• B. 1s and 2p_x
• C. 2p_y and 2p_y
• D. 1s and 2s

Answer 1

The Correct Option is C

To determine which of the given pairs will not form a sigma bond when considering the x-axis as the internuclear axis, we need to understand the basic concept of sigma bond formation.

Sigma (\(\sigma\)) bonds are covalent bonds formed by the head-on (end-to-end) overlap of atomic orbitals. The types of overlaps that typically form \(\sigma\) bonds include:

• \(s\)- and \(s\)-orbital overlap
• \(s\)- and \(p_x\)-orbital overlap (where \(p_x\) is aligned along the internuclear axis)
• \(p_x\)- and \(p_x\)-orbital overlap

Now, let's analyze each option to determine if they can form a sigma bond:

1. 1s and 1s: This is a classic example of a sigma bond, formed by the end-to-end overlap of two \(s\)-orbitals.
2. 1s and 2p_x: This combination forms a sigma bond through the overlap of the spherical \(s\)-orbital with the linear \(p_x\)-orbital, as the \(p_x\)-orbital is aligned along the internuclear axis.
3. 2p_y and 2p_y: The \({p_y}\) orbitals are oriented perpendicular to the x-axis (internuclear axis). They will overlap side-to-side, which results in a \(\pi\) (pi) bond, not a \(\sigma\) bond. Therefore, they cannot form a \(\sigma\) bond.
4. 1s and 2s: Both are \(s\)-orbitals, and their overlap is end-to-end, which results in a sigma bond.

Hence, the pair of orbitals 2p_y and 2p_y will not form a sigma bond, as their overlap is not along the internuclear axis but rather perpendicular, leading to a pi bond formation instead.

Correct Answer: 2p_y and 2p_y