Question

What is the Lewis dot structure of `BH_3`? How many lone pair electrons are in this molecule? How many bonding pairs of electrons are in this molecule? How many lone pair electrons are at the central atom?

Answer 1

Well, there are 6 electrons to distribute in `BH_3`, however, `BH_3` does not follow the pattern of `"2-centre, 2 electron"` bonds.

Explanation:

Boron has 3 valence electrons, and hydrogen has the 1; thus there are 4 valence electrons. The actual structure of borane is as diborane `B_2H_6`, i.e. `{H_2B}_2(mu_2-H)_2`, in which there are `"3-centre, 2 electron"` bonds, bridging hydrogens which bind to 2 boron centres. I would suggest that you get your text, and read in detail how such a bonding scheme operates.

By contrast, in ethane, `C_2H_6`, there are enough electrons to form `7xx"2-centre, 2 electron"` bonds, i.e. the `C-C` linkage, and `6xx"C-H"` bonds.