Question

Use the MO diagrams of SO- and SO+ to predict which is likely to have the shorter bond length.

Answer 1

From MO of SO, wee that pi*(3p) molecular orbital is HOMO.

pi*(3p) is anti bonding molecular orbital.

Bond order = (Bonding electrons - antibonding electrons) / 2

thus

for  SO+, one electron remove from pi*(3p) and thus S-O bond order increases from SO and bond length decreases.

But

for SO-, one electron enter to the pi*(3p). so bond order bond order decreases.

therefore,

SO+ have the shorter bond length.