Question

The structure of diborane $({B_2}{H_6})$ contains:
A.Four 2C-2e bonds and two 3C-2e bonds
B.Two 2C-2e bonds and 3C-2e bonds
C.Two 2C-2e bonds and four 3C-2e bonds
D.Four 2C-2e bonds and four 3C-2e bonds.

Answer 1

Diborane is a chemical compound that consists of boron and hydrogen atoms. Its molecular formula is $({B_2}{H_6})$. The structure of diborane is based on hybridization.

Complete step by step answer:
Since the atomic number of boron is 5 and the electronic configuration of boron is in the ground state is $1{s^2},2{s^2},2{p^1}$. In the excited state, the electron from 2s orbital jumps in 2p orbital hence in the excited state the electronic configuration is $1{s^2},2{s^1},2p{}_x^1,2p_y^1,2p_z^0$ and it undergoes $s{p^3}$ hybridization.
The two half-filled hybrid orbitals of each boron atom overlap with the half-filled orbitals of hydrogen atom forming a normal covalent bond whereas third half-filled hybrid orbital of boron atom and vacant hybrid orbital of second boron atom overlap simultaneously with the half-filled orbital of H- atom, thus the electron cloud contain two electrons but spread over three atoms that why this bond is called three centres electron-pair bond. The structure of diborane.

The bond length of terminal B-H bond is 119pm. And the distance between two boron atoms is 178pm.

Hence the correct answer is option A.

Note:
Alternatively, according to X-ray diffraction studies, there are two types of hydrogen atoms i.e., four-terminal hydrogen atoms and two bridge hydrogen atoms. The four-terminal hydrogen atom forms a normal covalent bond with boron hence it is quite strong whereas each bridge hydrogen atom is bonded to two boron atoms by a pair of electrons. In other words there are three centre electron-pair bonds and due to resemblance with bananas, it is also known as a banana bond. The three centre electron-pair bond is quite different from the normal covalent bond hence it is a weak bond.