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:
- 1s and 1s: This is a classic example of a sigma bond, formed by the end-to-end overlap of two \(s\)-orbitals.
- 1s and 2px: 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.
- 2py and 2py: 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.
- 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 2py and 2py 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: 2py and 2py