Problem 16 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The structure of \(\mathrm{XeO}_{3}\) is(a) linear (b) planar (c) pyramidal (d) T-shaped

Step-by-Step Solution

Answer

Option (c) pyramidal is correct.

Step 1: Understand the Structure of the Molecule

The molecule in question is xenon trioxide, \(X\mathrm{eO}_{3}\). It consists of a central Xenon (Xe) atom bonded with three Oxygen (O) atoms.

Step 2: Determine the Valence Electrons

Xenon, being in Group 18, has 8 valence electrons, and each oxygen atom has 6 valence electrons. Therefore, for Xe, \(XeO_{3}\), the total valence electron count is \(8 + 3 \times 6 = 26\).

Step 3: Apply the VSEPR Theory

Using the VSEPR (Valence Shell Electron Pair Repulsion) theory, we consider the electron pairs around the central Xenon atom. Xe has three bonding pairs (Xe-O) and one lone pair.

Step 4: Predict the Molecular Shape

Due to the three bond pairs and one lone electron pair, the geometry of XeO3 will be a distorted tetrahedron, which is described as a trigonal pyramidal shape. The lone pair arranges itself to minimize repulsion, pushing the other atoms into a pyramidal shape.

Step 5: Select the Correct Answer

Based on our analysis using the VSEPR theory, the structure of \(XeO_{3}\) is pyramidal due to the three bond pairs and one lone pair, making option (c) correct.

Key Concepts

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of molecules. It operates on the principle that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.
This theory helps chemists and students predict molecular shapes and angles between bonds, providing a 3D perspective of molecules. In the case of xenon trioxide (\(XeO_{3}\)), these electron repulsions can dictate how the atoms are oriented spatially.
To apply the VSEPR theory effectively:

• Count the valence electrons in the molecule.
• Determine the number of bonding and lone electron pairs.
• Use these to forecast the molecular shape based on minimizing electron-pair repulsion.

Through this approach, we can explain why molecules like \(XeO_{3}\), with three bonding pairs and one lone pair, have a distinctive pyramidal shape.

Valence Electrons

Valence electrons are the outermost electrons of an atom. They play a crucial role in chemical bonding and determine how atoms interact to form molecules. Understanding the behavior of these electrons allows chemists to predict molecular structures and properties.
Xenon (\(Xe\)) is a noble gas and typically has eight valence electrons. However, in compounds like xenon trioxide (\(XeO_{3}\)), it participates in bonding by sharing its electrons with oxygen atoms. Each of the three oxygen atoms contributes six valence electrons, making the total for \(XeO_{3}\) equal to 26.
This count is crucial when applying VSEPR theory, as it helps establish the number of bonding and lone pairs on the central atom. The electrons are arranged to ease repulsive forces, leading to the observed molecular geometry.

Trigonometric Pyramidal Shape

A trigonal pyramidal shape is a three-dimensional molecular geometry that arises when a molecule has three bonded pairs and one lone pair of electrons on the central atom. This shape is characterized by a central atom surrounded by three atoms forming a base of a pyramid, with the lone pair occupying a position above the base.
In xenon trioxide (\(XeO_{3}\)), the VSEPR theory helps us understand the pyramidal shape. The lone pair on xenon pushes the three oxygen atoms downward, creating a pyramid-like structure. This repulsion actually modifies the idealized tetrahedral angle of 109.5°, compressing it slightly due to the extra repulsive force exerted by the lone pair.
The trigonal pyramidal geometry is not only essential to chemistry learning but also relates to molecular polarity and reactivity, influencing how such molecules interact in various chemical environments.