Chapter 9, Problem 144RQ

The structure of the diborane molecule, B₂H₆, is sometimes drawn as

There are not enough valence electrons in the molecule to form eight single bonds, which is what the structure implies. Assuming that the boron atoms use $s{p}^3$ hybrid orbitals, suggest a way that hydrogen 1s orbitals can be involved in forming delocalized molecular orbitals that bridge the two boron atoms. Use diagrams to illustrate your answer. What would be the average bond order in the bridging bonds?