Problem 171 - A Complete Resource Book in Chemistry for JEE Main

Question

Number of lone pairs of electrons present in central atom of \(\mathrm{ClF}_{2}\) is

Step-by-Step Solution

Answer

Chlorine has 2 lone pairs of electrons in ClF₂.

Step 1: Determine Total Valence Electrons

Count the total number of valence electrons available for the molecules. Chlorine (Cl) belongs to group 17 and has 7 valence electrons. Fluorine (F) also belongs to the same group with 7 valence electrons each. Since there are two fluorines, they contribute a total of 14 electrons. Thus, the total number of valence electrons for ClF is \(7 + 7 \times 2 = 21\) electrons.

Step 2: Construct Lewis Structure

In the Lewis structure, we place Cl as the central atom surrounded by the two F atoms. Each Cl-F bond requires 2 electrons, so 4 electrons are used to form two bonds with the fluorines, resulting in \(21 - 4 = 17\) electrons remaining.

Step 3: Distribute Remaining Electrons

Distribute the remaining 17 valence electrons as lone pairs on the outer fluorines first to satisfy the octet rule: 16 electrons will make 8 lone pairs (4 on each fluorine). This leaves 1 electron left to place on the central chlorine atom.

Step 4: Determine Lone Pairs on Chlorine

Since the chlorine atom has used 2 valence electrons for bonding (1 electron from chlorine typically bonds with 1 electron from fluorine), and has 1 additional electron from remaining count, place these in pairs as lone pairs. This gives chlorine 4 electrons in 2 lone pairs. The chlorine atom has 2 lone pairs of electrons.

Key Concepts

Valence Electrons

Valence electrons are the electrons present in the outermost shell of an atom. These electrons play a crucial role in chemical bonding and reactions. Understanding how to count and utilize valence electrons is essential when working with molecules.

• The valence electrons determine how atoms interact and bind with each other.
• Atoms in the same group of the periodic table have the same number of valence electrons.
• For example, both chlorine (Cl) and fluorine (F) belong to group 17, meaning each has 7 valence electrons.

By adding the valence electrons of each atom in a molecule, you can determine the total number of electrons available for bonding. This is the first step in drawing a Lewis structure, where you arrange these electrons to show how atoms in the molecule bond together.

Lewis Structure

A Lewis structure is a diagram that represents the arrangement of atoms within a molecule, highlighting the bonded and lone electrons. It provides a visual representation of molecular bonding, aiding in understanding how molecules are structured.

• The central atom is usually the one with the lowest electronegativity, often bonded to the surrounding atoms.
• Bonds between atoms are represented by lines, where each line signifies two shared electrons.
• Lone pairs of electrons, or non-bonding pairs, are represented by dots around the atoms.

In the case of the \(\mathrm{ClF}_{2}\) molecule, chlorine (Cl) serves as the central atom, bonding with two fluorine (F) atoms. Initially, identify bonds and distribute electrons to form a stable structure, ensuring each atom has a full outer shell wherever possible.

Octet Rule

The octet rule is a chemical rule that reflects the tendency of atoms to have eight electrons in their valence shell. This rule provides stability to atoms and is a fundamental concept when drawing Lewis structures.

• Atoms achieve an octet configuration by gaining, losing, or sharing electrons.
• This rule is especially applicable to main-group elements, including chlorine and fluorine.
• In some cases, like in molecules with a central atom like chlorine in \(\mathrm{ClF}_{2}\), exceptions to the octet rule occur due to the availability of d orbitals in larger atoms.

While distributing remaining electrons in a Lewis structure, it's crucial to fulfill the octet rule for maximal stability. In \(\mathrm{ClF}_{2}\), both fluorine atoms meet this requirement first, and the remaining electrons are placed on the central chlorine atom.