Problem 10 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Identify the pair in which the geometry of the species is T-shape and square pyramidal, respectively (a) \(\mathrm{ICl}_{2}\) and \(\mathrm{ICl}_{5}\) (b) \(\mathrm{IO}_{3}^{-}\)and \(\mathrm{IO}_{2} \mathrm{~F}_{2}\) (c) \(\mathrm{ClF}_{3}\) and \(\mathrm{IO}_{4}\) (d) \(\mathrm{XeOF}_{2}\) and \(\mathrm{XeOF}_{4}\)

Step-by-Step Solution

Answer

The answer is option (a) \(\mathrm{ICl}_{2}^{-}\) and \(\mathrm{ICl}_{5}\).

Step 1: Understanding molecular geometries

T-shaped geometry is generally associated with molecules that have a central atom with 5 regions of electron density, including lone pairs, with the shape being AX3E2 (where A is the central atom, X is the bonded atoms, and E is the lone pairs). Square pyramidal geometry is common for molecules with 6 regions of electron density (AX5E), with one lone pair.

Step 2: Analyze each option

Go through each pair and determine the geometry based on VSEPR theory:a) \(\mathrm{ICl}_{2}^{-}\) has an AX2E3 structure (T-shaped), \(\mathrm{ICl}_{5}\) has an AX5E structure (square pyramidal).b) \(\mathrm{IO}_{3}^{-}\) has an AX3E1 structure (trigonal pyramidal), \(\mathrm{IO}_{2} \mathrm{F}_{2}\) has an AX3E2 structure (T-shaped).c) \(\mathrm{ClF}_{3}\) has AX3E2 structure (T-shaped), \(\mathrm{IO}_{4}^{-}\) has AX4E0 structure (tetrahedral).d) \(\mathrm{XeOF}_{2}\) has an AX3E1 structure (bent or T-shaped), \(\mathrm{XeOF}_{4}\) has an AX5E structure (square pyramidal).

Step 3: Identify the correct pair

From the analyses, the pair in option (a) has \(\mathrm{ICl}_2^{-}\) with a T-shaped geometry and \(\mathrm{ICl}_5\) with a square pyramidal geometry, satisfying both conditions of the exercise.

Key Concepts

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory is essential for predicting molecular geometry. This theory emphasizes minimizing repulsions between electron pairs surrounding a central atom. By minimizing these repulsions, molecules achieve specific three-dimensional shapes. VSEPR Theory suggests that the spatial arrangement of atoms in a molecule is determined by the number of regions of electron density around a central atom. These regions include both bond pairs and lone electron pairs.

According to VSEPR:

• "AX" represents bonded atoms, "E" symbolizes lone pairs on the central atom.
• Molecular geometry can range from linear to complex polyhedral structures depending on the AXE notation.
• The theory serves as a tool for predicting both simple and more intricate molecular shapes based on electron pair interactions.

VSEPR is a fundamental concept in chemistry, aiding students in visualizing molecular structures effectively. It explains why molecules like \(\mathrm{ICl}_{2}^{-}\) have a T-shaped structure, which we will explore next.

T-shaped Geometry

T-shaped geometry typically occurs in molecules with a central atom surrounded by five regions of electron density, classified as AX3E2. In these structures, three atoms are bonded to the central atom, accompanied by two lone pairs. The lone pairs occupy positions to maximize their distance, causing bonded atoms to form a T-like shape. This geometry is an outcome of balancing between electron pair repulsions.

Specifically for molecules like \(\mathrm{ClF}_{3}\):

• There's an axial position pair with strong lone pair repulsion pushing both downward.
• The bonded atoms are arranged in such a way to minimize these repulsions, forming a T-shape.
• Examples: \(\mathrm{ICl}_{2}^{-}\), \(\mathrm{ClF}_{3}\).

This helps illustrate how the VSEPR Theory prediction fits with these particular molecular structures.

Square Pyramidal Geometry

Square pyramidal geometry is another configuration predicted by VSEPR Theory, appearing in molecules with an AX5E configuration. Here, a central atom is bonded to five other atoms with one lone pair. The lone pair resides asymmetrically at one position, pushing the bonded atoms into the form of a square pyramid.

For example, \(\mathrm{ICl}_{5}\):

• This structure features four atoms forming the base of the pyramid.
• One atom at the apex with a lone pair exerting repulsion.
• Such lone pairs slightly distort ideal angles due to their electron cloud.

Consequently, molecules like \(\mathrm{ICl}_{5}\) demonstrate the square pyramidal structure. This geometry highlights the practical application of VSEPR Theory's principles in predicting molecular forms, aiding visualization and understanding of molecular behavior.