Question

Which of the following statements is not correct regarding the structure of diboranc? (1) Therc are two bridging hydrogen atoms in diboranc. (2) Each boron atom forms four bonds in diborane. (3) \Lambdall the hydrogen atoms are not in the same planc in diboranc. (4) \Lambdall B II bonds in diborane are similar.

Short answer

Statement 4 is not correct regarding the structure of diborane.

Step-by-step solution

- Analyze the Chemical Structure

Diborane (B2H6) is a molecule with a unique structure. To determine the incorrect statement, review the structure where two boron atoms are bonded to four terminal hydrogen atoms and two bridging hydrogen atoms.

- Evaluate Statement 1

The statement 'There are two bridging hydrogen atoms in diborane' must be assessed. Indeed, diborane has two hydrogen atoms that act as bridges between the two boron atoms.

- Evaluate Statement 2

Consider the bonding of boron. Each boron is bonded to three hydrogen atoms (two terminal and one bridge) and one other boron atom. Evaluate if each boron forms four bonds in diborane.

- Evaluate Statement 3

Examine the spatial arrangement. Due to bridging hydrogens, not all hydrogens lie in the same plane.

- Evaluate Statement 4

Review the nature of B-H bonds. The terminal B-H bonds are single covalent bonds, whereas bridging B-H bonds are three-center two-electron bonds. Assess the similarity of all B-H bonds in diborane.

- Identify the Incorrect Statement

In conclusion, identify the statement that is inconsistent with the known structure and bonding of diborane.

Key concepts

Bridging Hydrogen Atoms

Diborane (B2H6) has a fascinating molecular structure. One key feature is the presence of **bridging hydrogen atoms**.
There are two hydrogen atoms that bridge between boron atoms.
These hydrogen atoms are unique because they are involved in bonds that are different from typical covalent bonds.
This kind of bond is called a **three-center two-electron bond**.
Meaning, a single pair of electrons is shared between two boron atoms and one hydrogen atom.
This unique bonding arrangement helps to hold the diborane molecule together.
It also explains its distinct properties.

Boron Bonding

In diborane, each boron atom shows a distinctive bonding pattern.
Every boron atom forms a total of four bonds.
Here's how these bonds are structured:
- Two **terminal hydrogen atoms** are linked to each boron with regular single covalent bonds.
- One **bridging hydrogen** forms a three-center two-electron bond, connecting it with the other boron atom.
- The two boron atoms are also bonded directly to each other.
This creates a robust structure due to the multi-center bonding prevalent in **diborane**.

B-H Bonds

The **B-H bonds** in diborane are essential to understand: they come in two distinct types.
- **Terminal B-H Bonds**: These are regular, two-center two-electron single bonds.
Each boron directly connects to two hydrogens in this way.
- **Bridging B-H Bonds**: As mentioned earlier, these are three-center two-electron bonds.
They form a bridge between the two boron atoms using one pair of electrons.
This distinction in bonding types adds complexity to the molecule.
But it is crucial for its structural integrity and chemical behavior.

Spatial Arrangement of Hydrogens

The spatial arrangement of hydrogen atoms in **diborane** is quite interesting.
Due to the unique bonding structures, not all the hydrogen atoms in diborane lie in the same plane.
Here's how they are arranged:
- The **terminal hydrogen atoms** are in one plane, bonded directly to the boron atoms.
- The **bridging hydrogen atoms** sit in a separate plane, above and below the plane containing the boron atoms.
This results in the molecules having a staggered arrangement.
Driving the characteristic three-dimensional shape of the diborane molecule.
This non-planar arrangement is pivotal for understanding the molecule's reactivity and interactions.