Question

On the basis of VBT explain the structure of Diborane.

Answer 1

Valence Bond Theory

• In a molecule, electrons inhabit atomic orbitals rather than molecular orbitals.
• It is based on the concept of bond overlapping.
• Covalent bonding is a chemical link generated by the sharing of electrons.

Postulates:-

• When two valence orbitals present in two separate atoms overlap on one other, the covalent bonds are created.
• Due to this overlapping, the electron density between the two bonding atoms increases, increasing the stability of the resulting molecule.
• The valence shell of an atom has several unpaired electrons, allowing it to make many bonds with other atoms and the paired electrons present in the valence shell do not participate in the creation of chemical bonds
• Covalent chemical bonds are directional and are also parallel to the region corresponding to the atomic orbitals that are overlapping.
• The pi bonds are formed from sidewise overlapping whereas the overlapping along the axis containing the nuclei of the two atoms leads to the formation of sigma bonds.

Structure of Diborane according to VBT:

• The chemical formula of Diborane is ${\mathrm{B}}_2{\mathrm{H}}_6$.
• The atomic number of Borane is 5 and the electronic configuration can be written as $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^1$.
• During bond formation, the one-electron gets excited to the $2\mathrm{p}$ orbital and will have four ${\mathrm{sp}}^3$ hybrid orbitals, out of which three is having one electron each and one orbital is empty.

• Each Borane forms two covalent bonds with Hydrogen and is now left with two orbitals, one having an empty orbital and the other having one electron.
• Due to unpaired electrons orbital and empty orbitals of two Borane atoms, a banana bond will form.