Problem 53 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following is a correct set with respect to molecule, hybridization and shape? (a) \(\mathrm{BeCl}_{2}, \mathrm{sp}^{2}\), linear (b) \(\mathrm{BeCl}_{2}, \mathrm{sp}^{2}\), triangular planar (c) \(\mathrm{BCl}_{3}, \mathrm{sp}^{2}\), triangular planar (d) \(\mathrm{BCl}\). \(\mathrm{sp}^{3}\). tetrahedral

Step-by-Step Solution

Answer

Option (c): \(\mathrm{BCl}_{3}, \mathrm{sp}^{2}\), triangular planar is correct.

Step 1: Analyze the options

We need to review each option carefully. The options involve molecular examples, corresponding hybridization, and geometrical shapes. For each molecule, we should check what type of hybridization it undergoes and its resultant shape.

Step 2: Investigate \(\mathrm{BeCl}_{2}\) Configuration

\(\mathrm{BeCl}_{2}\) is a molecule where beryllium (\(\mathrm{Be}\)) has 2 electrons in its outer shell. In \(\mathrm{BeCl}_{2}\), \(\mathrm{Be}\) uses \(\mathrm{sp}\) hybridization to form two \(\sigma\)-bonds with chlorine atoms. The geometry is linear.

Step 3: Check \(\mathrm{BCl}_{3}\) Configuration

\(\mathrm{BCl}_{3}\) is a molecule where boron (\(\mathrm{B}\)) has 3 outer electrons. In \(\mathrm{BCl}_{3}\), \(\mathrm{B}\) undergoes \(\mathrm{sp}^2\) hybridization, which involves the mixing of one \(s\) orbital and two \(p\) orbitals, resulting in a planar triangular shape.

Step 4: Validate Other Options

\(\mathrm{BeCl}_{2}\) configurations in options (a) and (b) are incorrect because \(\mathrm{BeCl}_{2}\) is linear, not angular or triangular planar. Option (d) involving \(\mathrm{BCl}\) is also incorrect; \(\mathrm{BCl}\) mentioned as \(\mathrm{sp}^{3}\) tetrahedral does not exist with such a configuration in common chemistry contexts.

Step 5: Determine the Correct Option

Based on steps 2 and 3, the correct configuration for \(\mathrm{BCl}_{3}\) is \(\mathrm{sp}^2\) hybridization with a triangular planar shape.

Key Concepts

Hybridization

Hybridization is a fundamental concept in chemistry that explains how atomic orbitals of an atom mix to form new orbitals, which can then form bonds with other atoms. Understanding this concept helps explain the shapes and structures of molecules :

• The process involves combining different atomic orbitals (like s and p orbitals) into a new set of hybrid orbitals with equivalent energy.
• The type of hybridization determines the geometry of the molecule. For example, sp hybridization leads to a linear shape, while sp² leads to a trigonal planar shape.
• Hybridization occurs to lower the energy of the molecule by maximizing the overlap of atomic orbitals, which enhances bonding.

To determine hybridization, consider the number of atoms bonded and lone pairs of electrons present on the central atom. For instance, two areas of electron density imply sp hybridization, resulting in a linear shape.

BCl3 structure

In the molecule of boron trichloride (BCl₃), boron is the central atom and forms three bonds with chlorine atoms. Boron has three electrons in its outer shell that undergo sp² hybridization:

• This hybridization strategy involves one s orbital and two p orbitals of boron combining to create three sp² hybridized orbitals.
• The resulting geometry is trigonal planar, with each bond angle being 120 degrees.

The planar shape is essential for minimizing repulsion between the electron pairs around boron. As a result, BCl₃ is perfectly symmetrical, which also means it's non-polar. Further, this arrangement allows max overlap of orbitals, ensuring strong covalent bonds in the molecule.

BeCl2 structure

Beryllium chloride (BeCl₂) is a simple example that showcases the concept of hybridization and its role in determining molecular shape:

• Beryllium, the central atom, typically would not form more than two bonds because of its 2-valence electron configuration.
• In BeCl₂, beryllium undergoes sp hybridization, which involves one s and one p orbital forming two equivalent and linear sp hybridized orbitals.
• This results in a linear shape where chlorine atoms are placed at a 180-degree angle from each other.

The linear configuration minimizes repulsions between bonded electron pairs on beryllium. In the gas phase, this linear shape remains, but in the solid state, the arrangement can change due to intermolecular forces and crystal packing. Understanding such configurations helps explain both molecular behavior and interactions.