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

Short answer

(c) 2.

Step-by-step solution

Determine the Total Valence Electrons

First, find the total number of valence electrons for the molecule \(\mathrm{ClF}_{3}\). Chlorine (Cl) has 7 valence electrons, and each fluorine (F) also has 7 valence electrons. Since there are 3 fluorine atoms, the total number of electrons is \(7 (\text{from Cl}) + 3 \times 7 (\text{from F}) = 28\) electrons.

Form Bonds and Count Electrons Used

In \(\mathrm{ClF}_{3}\), chlorine bonds with three fluorine atoms. Each bond uses 2 electrons, thus 3 bonds use \(3 \times 2 = 6\) electrons from the total pool.

Calculate Remaining Electrons

Subtract the electrons used in bonding from the total count: \(28 - 6 = 22\) electrons. These electrons remain to be distributed as lone pairs.

Distribute Electrons As Lone Pairs

Assign 6 electrons (3 lone pairs) to each of the 3 fluorine atoms. This uses \(3 \times 6 = 18\) electrons. Now, \(22 - 18 = 4\) electrons remain for chlorine.

Identify Lone Pairs on Central Atom

The remaining 4 electrons are assigned as 2 lone pairs on chlorine because 4 electrons equal 2 pairs.

Key concepts

Valence Electrons and Their Importance

Valence electrons are the electrons present in the outermost shell of an atom. These electrons play a crucial role in determining how atoms bond with each other.
Understanding valence electrons is vital when exploring molecular structures and chemical reactions, as they are the participants in bond formation with other atoms. For example, in the molecule \( \mathrm{ClF}_{3} \), chlorine and fluorine each have 7 valence electrons, contributing to the molecule's overall structure.
By knowing the total number of valence electrons, chemists can predict how these atoms will share or transfer electrons to achieve stable configurations, resembling the nearest noble gas electron configuration.

Understanding Molecular Geometry

Molecular geometry is the three-dimensional arrangement of atoms in a molecule. This concept helps us determine the molecule's shape, which influences its chemical properties and reactivity.
VSEPR (Valence Shell Electron Pair Repulsion) theory is used to predict molecular geometry based on the repulsion between electron pairs surrounding a central atom. According to this theory, electron pairs rearrange themselves in space to minimize repulsion, enabling the determination of the molecule's exact shape.
For instance, \( \mathrm{ClF}_{3} \) has a T-shaped molecular geometry. Chlorine, being the central atom, bonds with three fluorine atoms and also holds lone pairs, which affects the geometry.

The Role of Electron Pairs

Electron pairs, including both bonding pairs and lone pairs, define how atoms make bonds in a molecule.
A bonding pair is a pair of electrons shared between two atoms, forming a covalent bond. Each bond typically uses one electron from each atom involved. Meanwhile, lone pairs are not involved in bonding and are instead located on the central atom.
In \( \mathrm{ClF}_{3} \), the central chlorine atom forms three bonds with fluorines, thereby using three pairs as bonding pairs. The rest of the electrons are organized into lone pairs, influencing the molecule's geometry and properties.

Understanding Lone Pairs

Lone pairs are pairs of valence electrons that aren't shared with other atoms, residing solely on one atom. They are significant because they affect molecular shape and reactivity.
Lone pairs tend to repel other electron pairs more strongly than bonding pairs. This increased repulsion can lead to adjustments in bond angles, altering the geometric arrangement of the molecule.
In the molecule \( \mathrm{ClF}_{3} \), after accounting for bonding electrons, the remaining electrons form two lone pairs on the central chlorine atom. These lone pairs contribute to the molecule's T-shaped structure by pushing the bonded atoms into a specific configuration to minimize electron pair repulsion.