Answer to Question #79250 in General Chemistry for Rs2000

Question

Why 2p 2p overlap is better than 3p 3p overlap?. If so then why in f2 and cl2 we observe cl2 has more bond energy than in f2 even though the former is 2p 2p overlap?

Answer 1

F-F is interesting in its own right, and that bond is weak, and F2 has been responsible for the loss of more fingers than probably any other compound.

If you put two electrons in a bond, and two in an antibond, this is a repulsive interaction (this is what causes sterics - a steric repulsion is a filled-filled interaction). It turns out that the shorter the bond, the more ridiculous the gap between bonding stabilization and antibonding de-stabilization gets. If your bonds are long, bonding and antibonding are close to a wash. So when you get to Cl2, the pi-bonding is minimal, but so is the pi* antibonding. So that bond isn't weakened much by this effect.