Question

Identify the statement that is correct as far as structure of diborane is concerned. (1) All B - H bonds in diborane are similar (2) The hydrogen atoms are not in the same plane in diborane (3) There are two bridging hydrogen atoms in diborane (4) Each boron atom forms four bonds in diborane (a) 1,2 (b) \(1,2,3\) (c) \(2,3,4\) (d) \(1,3,4\)

Short answer

Correct statements are (2, 3, 4). Answer: (c) 2,3,4.

Step-by-step solution

Understanding Diborane Molecular Structure

Diborane is a chemical compound with the formula \( B_2H_6 \). It has a unique structure often characterized by two boron atoms and six hydrogen atoms arranged such that not all \( B - H \) bonds are the same. This is because it features terminal (normal) \( B - H \) bonds as well as bridging \( B - H - B \) bonds.

Analyzing the Plane of Hydrogen Atoms

In diborane, the hydrogen atoms attached directly to the boron atoms (the terminal hydrogens) are not in the same plane as the two bridging hydrogens. In fact, the diborane structure is often described in terms of being 'banana-shaped' due to the position of the bridging hydrogens.

Identification of Bridging Hydrogens

Diborane includes two bridging hydrogen atoms. These hydrogens are shared between the two boron atoms, forming two three-center, two-electron bonds. This unique bonding is a key feature of diborane.

Boron Atom Bonding Count

Each boron atom in diborane forms four bonds. In detail, one boron forms two terminal \( B - H \) bonds and participates in two \( B - H - B \) bridge bonds. This results in a total of four bonds for each boron.

Select the Correct Statement

Considering the statements:(1) All \( B - H \) bonds in diborane are similar is incorrect as there are terminal and bridging \( B - H \) bonds.(2) The hydrogen atoms are not in the same plane in diborane is correct.(3) There are two bridging hydrogen atoms in diborane is correct.(4) Each boron atom forms four bonds in diborane is correct.Thus, the correct statements are 2, 3, and 4.

Key concepts

Bridging Hydrogen Atoms

In the unique structure of diborane (\( B_2H_6 \)), one of the most intriguing features is the presence of bridging hydrogen atoms. These hydrogen atoms are not like any regular hydrogen in chemical structures. They "bridge" between two boron atoms, creating what is known as the bridging \( B-H-B \) bonds. Normally, you would expect hydrogen to form a simple one-to-one bond with another atom. However, in diborane, things are a little different.
- These bridging hydrogens sit between two boron nuclei.- They form bonds with two borons simultaneously.- This arrangement leads to a unique type of bonding.
In terms of molecular geometry, these bridging hydrogen atoms cause the structure to appear "banana-shaped" compared to traditional bonding arrangements. This shape is a result of the need for the bridging hydrogens to stay stable while maintaining their unusual bonds with both boron atoms.

Boron Atom Bonding

In diborane, boron atom bonding is anything but ordinary. Each of the two boron atoms finds itself in a scenario consisting of both typical and atypical bonds. A single boron atom in this compound establishes four bonds: two are normal, direct bonds with hydrogen atoms which we term as terminal \( B-H \) bonds, and two are bridging bonds known as \( B-H-B \).
- Terminal \( B-H \) bonds are straight connections between a boron atom and a hydrogen atom.- Bridging bonds involve the sharing of a hydrogen atom between two boron atoms.
It's important to remember that while all the bonds involve borons, not all \( B-H \) bonds are the same. The innovation in diborane bonding mainly stems from these bridging interactions, which enable boron to achieve its four-bond arrangement in a stable manner.

Three-Center Two-Electron Bonds

One of the fascinating aspects of the diborane (\( B_2H_6 \)) structure is the phenomenon of three-center two-electron (3c-2e) bonds. These bonds are central to understanding why diborane can stably exist despite its unconventional appearance. Typically, most bonds form with one pair of electrons shared between two atoms. But, diborane challenges this norm.
- In a 3c-2e bond, a single pair of electrons is shared across three atoms.- Within diborane, these three atoms include two boron atoms and one bridging hydrogen atom.
To visualize this, imagine a traditional bond with two atoms, but this time, an additional atom (the bridging hydrogen) swoops in to share the single electron pair. Therefore, the electron pair holds together three atoms, forming a bond that seems unusual but is crucial to the structure's integrity. This bonding type is key for the stability in compounds like diborane with bridging hydrogen atoms.