Question

Section 10.2 discusses - bonds and $\sigma$- bonds for p - states and $\pi$-bonds for s-states but not $\sigma$- bonds for $\pi$ - states. Why not?

Short answer

Because p states can exist in 3 different orientations and s - states can only exist in one orientation.

Step-by-step solution

Description of the charge Density of These States

All $\mathit{\pi }$- bonds are defined as the states where the charge density is largely off the molecular axis.

Description of  s– States

All s- states have their charge densities largest along the molecular axis and thus only have $\sigma$- bonds.

Description of  p – States

Since p- states can have three different orientations, after picking one of them as the axis, the molecular states of the other two will have charge density largely off the molecular axis, which are $\pi$ - bonds.

Hence $\pi$- bonds exist for p– states but do not for s – states.