Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

The planar structure of \(\mathrm{BF}_{3}\) can be explain by the fact that \(\mathrm{BF}_{3}\) is (a) sp hybridized (b) sp \(^{2}\) hybridized (c) sp \(^{3}\) hybridized (d) sp \(^{3}\) hybridized

Step-by-Step Solution

Answer

The planar structure of \(\mathrm{BF}_{3}\) is due to \(\text{sp}^2\) hybridization.

Step 1: Analyze the Given Molecule

The molecule in question is \(\mathrm{BF}_{3}\), or boron trifluoride. It is a compound of boron surrounded by three fluorine atoms.

Step 2: Determine the Central Atom's Electron Configuration

Boron, the central atom, has an atomic number of 5, with an electron configuration of \([1s^2 2s^2 2p^1]\). This suggests boron has three valence electrons available for bonding.

Step 3: Calculate the Number of Hybrid Orbitals

In \(\mathrm{BF}_{3}\), boron forms three sigma bonds with fluorine atoms. This requires three equivalent hybrid orbitals, indicating \(\mathrm{sp}^2\) hybridization, since \(\mathrm{sp}^2\) provides three hybrid orbitals: one \(s\) and two \(p\).

Step 4: Relate Hybridization to Molecular Shape

\(\mathrm{sp}^2\) hybridization results in a trigonal planar shape, which corresponds to \(\mathrm{BF}_{3}\)'s planar structure.

Step 5: Confirm with VSEPR Theory

According to VSEPR theory, the geometry of three bonded pairs around the central atom, with no lone pairs, results in a trigonal planar shape, consistent with \(\mathrm{sp}^2\) hybridization.

Key Concepts

BF3 molecular geometry

Borondifluoride, or \( \text{BF}_3 \), is a molecule that showcases a simple yet elegant geometry known as trigonal planar. This geometry occurs because of how the atoms are arranged around the central atom, boron. In \( \text{BF}_3 \), the boron atom is surrounded equally by three fluorine atoms. This creates a flat triangular shape where each fluorine atom is at each corner of the triangle.

In this structure, the bond angles are all 120°, providing symmetry and balance. The boron atom is on the same plane as the three fluorine atoms, hence the name "planar." This arrangement minimizes repulsion between the bonding pairs, resulting in a stable molecular structure. The planar structure is essential for \( \text{BF}_3 \) as it plays a role in its reactivity and interaction with other molecules, particularly in chemical reactions where it often acts as a Lewis acid.

sp2 hybridization

To understand \( \text{BF}_3 \)'s geometry, we need to examine the concept of \( \text{sp}^2 \) hybridization. Hybridization is a process that describes the mixing of atomic orbitals to produce new hybrid orbitals. These hybrids are key in forming molecular bonds. When we say \( \text{sp}^2 \) hybridization, we refer to the blending of one s orbital and two p orbitals from the boron atom.

This process creates three equivalent \( \text{sp}^2 \) hybrid orbitals. Each of these orbitals forms a sigma bond with an orbital from a fluorine atom in \( \text{BF}_3 \).

• The hybrid orbitals align 120° apart, creating a planar and symmetrical molecular structure.
• The remaining unhybridized p orbital doesn’t participate in bonding directly, but its presence is crucial for other chemical properties like electronic interactions.

The \( \text{sp}^2 \) hybridization helps us understand \( \text{BF}_3 \)'s stability and geometry, reinforcing the role of valence electrons in shaping molecular structures.

VSEPR theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the shape of molecules. The theory is based on an intuitive understanding: Because electron pairs repel each other, molecules adjust their shape so that these repulsions are minimized. In \( \text{BF}_3 \), VSEPR theory helps explain its planar geometry.

• The boron atom in \( \text{BF}_3 \) forms three bonding pairs with fluorine atoms.
• There are no lone pairs on the boron, which is crucial because lone pairs typically have stronger repulsive forces compared to bonding pairs.

According to VSEPR theory, when there are three pairs of bonded electrons and no lone pairs, the most effective arrangement to minimize repulsion is a trigonal planar shape.

This theory elegantly complements the concept of \( \text{sp}^2 \) hybridization, as both show how electrons strive for a balance that dictates overall molecular geometry. VSEPR provides a useful framework for predicting molecular shapes just by considering electron pair interactions, making it an invaluable tool in chemistry.