Problem 23 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The geometry and the type of hybrid orbital present about the central atom in \(\mathrm{BF}_{3}\) is (a) linear, \(s p\) (b) trigonal planar, \(s p^{2}\) (c) tetrahedral, \(s p^{3}\) (d) pyramidal, \(s p^{3}\).

Step-by-Step Solution

Answer

(b) trigonal planar, \(sp^2\).

Step 1: Identify the Central Atom

In the molecule \(\mathrm{BF}_3\), the central atom is Boron (B). This is because Boron is less electronegative than Fluorine and typically forms the core structure from which other atoms are arranged.

Step 2: Count Valence Electrons

Boron (B) has 3 valence electrons, while each Fluorine (F) atom has 7 valence electrons. Therefore, the total number of valence electrons in \(\mathrm{BF}_3\) is \(3 + 3 \times 7 = 24\) valence electrons.

Step 3: Determine Electron Pair Arrangement

The three valence electrons of Boron form single covalent bonds with each of the three Fluorine atoms. This results in Boron being surrounded by three bond pairs, which positions the Fluorine atoms around Boron, minimizing electron pair repulsion, to form a planar triangular shape.

Step 4: Identify Geometry of the Molecule

With three regions of electron density around the central atom (Boron) and no lone pairs affecting the molecular geometry, the structure forms a trigonal planar shape according to VSEPR (Valence Shell Electron Pair Repulsion) theory.

Step 5: Identify Hybridization of the Central Atom

To achieve the trigonal planar structure, Boron undergoes \( sp^2 \) hybridization. This involves mixing one s orbital and two p orbitals to form three \( sp^2 \) hybrid orbitals.

Step 6: Choose the Correct Answer

Considering the findings, \(\mathrm{BF}_3\) exhibits a trigonal planar molecular geometry with \( sp^2 \) hybridization for the central atom Boron. Thus, the correct option is (b) trigonal planar, \(sp^2\).

Key Concepts

Hybridization

Hybridization is a concept in chemistry that describes the merging of orbitals to form new, equivalent hybrid orbitals. This occurs in atoms when they bond to form molecules. By understanding hybridization, we can predict the shape and bonding patterns of molecules.

In the case of \(\mathrm{BF}_3\), Boron, as the central atom, undergoes \(sp^2\) hybridization. This means one of Boron's s orbitals merges with two of its p orbitals. This merging creates three equivalent \(sp^2\) hybrid orbitals. These orbitals are arranged in a plane, 120 degrees apart, providing stability and the best arrangement for minimizing electron repulsion.

The goal of hybridization is to allow for the optimal bonding and layout for atoms in a molecule. Through understanding hybridization, chemists can predict the geometry and potential reactivity of different molecular structures.

Trigonal Planar

A trigonal planar arrangement is a common geometry for molecules where the central atom is bonded to three peripheral atoms. In this structure, all atoms lie in the same plane, forming a roughly triangular shape with 120-degree angles between bonds.

In \(\mathrm{BF}_3\), the trigonal planar shape is achieved due to the Boron atom forming bonds with the three Fluorine atoms using its \(sp^2\) hybridized orbitals. Each of the fluorine atoms is positioned at the corners of an equilateral triangle when viewed from above.

This shape is important because it influences the molecule's properties, including polarity and reactivity. In the case of \(\mathrm{BF}_3\), the symmetry of a trigonal planar shape means the molecule is nonpolar, despite the large electronegativity difference between Boron and Fluorine.

VSEPR Theory

VSEPR stands for Valence Shell Electron Pair Repulsion theory. It is a model used to predict the shape of individual molecules based on the repulsion between the electron pairs in the valence shell of atoms.

According to VSEPR theory, molecules will adjust their shapes so that electron pairs are as far apart as possible, minimizing repulsion. This is crucial in determining molecular geometry. \(\mathrm{BF}_3\) is a perfect example, where using VSEPR theory, we predict a trigonal planar geometry due to the three bonding pairs of electrons around the boron atom.

VSEPR theory helps explain why molecules have particular shapes and can account for physical properties such as angles between bonds and the molecules' reactivity. By applying this theory, chemists can predict and visualize how molecules look three-dimensionally.