Question #d5075

1 Answer
Sep 15, 2016

Answer:

Here's my explanation.

Explanation:

The geometry of #"B"_2"H"_6# is

upload.wikimedia.org

Each #"B"# atom has a tetrahedral arrangement of bonds, so it is reasonable to assume an #sp^3# hybridization.

B2H6
(From wps.prenhall.com)

But it is a distorted tetrahedron. The bridging #"H-B-H"# bond angles are 97°, but the outer #"H-B-H"# bond angles are 120 °.

The bridging bonds are banana bonds.

To understand the bond angles, recall the discussion of banana bonds in the structure of cyclopropane.

The four bonds between the two #"B"# atoms and the two bridging #"H"# atoms "want" to get close to a square, so the internal bond angle will settle on some value between 90° and 109.5°.

The inner #sp^3# orbitals get a little more #p# character, and the internal #"H-B-H"# bond angles decrease by about 12°.

Thus, the outer #sp^3# orbitals get a little more #s# character, and the outer #"H-B-H"# bond angles increase by about 11° to 120°.

That the angle is the same as the #sp^2# bond angle is just a coincidence.

Molecular Orbital theory gives a better explanation of the structure of #"B"_2"H"_6#, as in the video below.