Problem 73 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of lone pairs of electrons present in central atom of \(\mathrm{ClF}_{3}\) is (a) 0 (b) 1 (c) 2 (d) 3

Step-by-Step Solution

Answer

There are 2 lone pairs on the central chlorine atom.

Step 1: Determine the Central Atom

In the molecular formula \(\mathrm{ClF}_3\), chlorine (Cl) is the central atom because it is the less electronegative atom compared to fluorine (F).

Key Concepts

Electron Pairs

Electron pairs are groups of two electrons that occupy the same orbital in an atom or molecule. These pairs are crucial in determining the shape and structure of a molecule. In VSEPR (Valence Shell Electron Pair Repulsion) theory, electron pairs, which include both bonding pairs and lone pairs, are used to predict molecular geometry. There are two types of electron pairs:

• Bonding pairs are shared between atoms where they participate in chemical bonds, holding the atoms together.
• Lone pairs, also known as non-bonding pairs, are not involved in bonding. They reside on a single atom, influencing the molecule's geometry by repelling other electron pairs.

To understand electron pairs, consider the molecule \(\mathrm{ClF}_3\). Chlorine has 7 valence electrons, and 3 of these form bonds with fluorine atoms, resulting in 3 bonding pairs. The remainder form lone pairs. Lone pairs have a substantial impact on the molecular shape due to their tendency to occupy more space than bonding pairs, leading to distortions in angles within the molecule.

Molecular Geometry

Molecular geometry refers to the 3-dimensional arrangement of atoms in a molecule. This geometry is determined by the number of electron pairs surrounding the central atom, including both bonding and lone pairs. For example, in \(\mathrm{ClF}_3\), molecular geometry is influenced by VSEPR theory, which predicts how electron pairs will spatially arrange themselves to minimize repulsion.

• The electron pair geometry around chlorine in \(\mathrm{ClF}_3\) is trigonal bipyramidal, but due to the presence of lone pairs, the molecular geometry is distorted.
• ClF\(\_3\) typically adopts a T-shaped molecular geometry due to the presence of 3 bonding pairs and 2 lone pairs.

Understanding molecular geometry is essential, as it impacts a molecule's chemical properties and reactions. The shape affects the dipole moment and intermolecular forces, influencing how molecules interact with each other.

Valence Electrons

Valence electrons are the outermost electrons of an atom that are involved in chemical bonding. These electrons play a pivotal role in determining how an element will react with others.

• For instance, chlorine has 7 valence electrons while fluorine has 7 as well, but chlorine is central to \(\mathrm{ClF}_3\) because it can share more electrons.
• In \(\mathrm{ClF}_3\), chlorine shares three of its valence electrons with fluorine's valence electrons, contributing to bond formation.

Valence electrons dictate the electron configuration of atoms in molecules and are crucial in covalent bonding. When atoms interact, they often seek to complete their octet, achieving stability similar to noble gases.

Chemical Bonding

Chemical bonding refers to the interactions that hold atoms together in compounds. It's primarily facilitated through the sharing or transfer of electrons.

• Covalent bonds result when two atoms share electron pairs to achieve stability.
• In \(\mathrm{ClF}_3\), chlorine and fluorine form covalent bonds, sharing electrons to stabilize the molecule.

The strength and type of chemical bond contribute to the molecule's physical properties and reactivity. In \(\mathrm{ClF}_3\), the strong covalent bonds provide stability, while the lone pairs and bond angles influence how it reacts with other substances. Chemical bonding is crucial to understanding the structure, behavior, and interaction of molecules in chemistry.