Question

The type of hybridisation of boron in diborane is (a) \(s p\) (b) \(s p^{2}\) (c) \(s p^{3}\) (d) \(d s p^{2}\)

Short answer

The hybridization of boron in diborane is \(sp^2\).

Step-by-step solution

Understand the Structure of Diborane

Diborane, \(B_2H_6\), has a unique structure with two boron atoms and six hydrogen atoms. The molecule is generally considered to have two boron atoms linked by two hydrogen atoms in a bridge formation.

Determine the Electron Pair Geometry around Boron

Each boron atom in diborane is surrounded by three hydrogen atoms, two of which are terminal, and one acts as a bridge. Given that each boron atom forms three bonds, we initially consider the electron pair geometry around each boron atom.

Identify the Type of Hybridization

Since each boron atom forms three bonds in diborane and has no lone pairs, the hybridization corresponds to having three hybrid orbitals. This typically indicates \(sp^2\) hybridization, as it provides three orbitals for bonding.

Choose the Correct Answer

Based on the hybridization determined, the correct choice for the hybridization type of boron in diborane is \(s p^{2}\). Therefore, the answer is option (b).

Key concepts

Diborane

Diborane, represented by the chemical formula \( B_2H_6 \), is a fascinating molecule that challenges our understanding of molecular geometry and hybridization. It is an electron-deficient compound where the boron atoms do not possess enough valence electrons to form typical covalent bonds. One key feature of diborane is its unique three-centered two-electron (3c-2e) bonds, known as banana bonds, which involve two boron atoms and a bridging hydrogen atom.
The structure of diborane can be visualized as two boron atoms linked by two bridging hydrogen atoms, with the remaining four hydrogen atoms attached terminally to the boron atoms. This formation makes diborane a prime example of a molecule with unconventional bonding, as it doesn't fit neatly into the standard octet rule.

Boron

Boron, a group 13 element, is crucial in forming compounds like diborane. It has three valence electrons, which means it typically forms three bonds. In diborane, each boron atom utilizes all its valence electrons to participate in the formation of the 3c-2e bonds with hydrogen.
Due to its limited number of valence electrons, boron often forms electron-deficient compounds like diborane. In these cases, boron must utilize hybridization to maximize the effectiveness of its electron sharing.
The hybridization of boron in diborane is particularly interesting because it involves \( sp^2 \) hybridization. This results in the formation of three hybrid orbitals per boron atom, each used for bonding with either a terminal hydrogen atom or participating in the banana bond with the bridging hydrogens. Boron's ability to engage in such unique bonding formats underlines its versatility as a chemical element.

Molecular geometry

Understanding the molecular geometry of diborane requires a consideration of both its bridges and terminal bonds. The combination of \( sp^2 \) hybridization and 3c-2e bonds makes the geometry of diborane quite different from simpler molecules.
Each boron atom in diborane adopts a trigonal planar configuration due to \( sp^2 \) hybridization. However, the presence of the bridge hydrogen atoms distorts this geometry slightly.

• The terminal hydrogen bonds, which are linear, contribute to the stability of the molecule.
• The bridge hydrogens introduce a bend in the overall geometry, creating an angle, giving diborane a unique geometry.

Overall, diborane is a prime example of how variations in atomic bonding and hybridization can lead to complex and interesting molecular shapes.