Explain why `BF_(3)` exist but `BH_(3)` does not.

Explanation

Boron fluoride exists as `BF_(3)` which is quite stable. This is because of `p pi-p pi` back bonding between filled 2pi orbtial of fluorine and vacant 2p orbital of boron. But not back bonding is possible between. 1s orbital of hydrogen as 2p orbtial of boron. this means that `BH_(3)` is not stable it exists as a dimer in the form of diborane `(B_(2)H_(6))`. for its structure, consult section 11.4.