Problem 180 - A Complete Resource Book in Chemistry for JEE Main

Question

The structure of \(\mathrm{XeO}_{3}\) is (a) linear (b) planar (c) pyramidal (d) T-shaped \([2007]\)

Step-by-Step Solution

Answer

The structure of \(\text{XeO}_3\) is pyramidal (c).

Step 1: Determine the Valence Electrons of Xenon

Xenon (Xe) is a noble gas and is in Group 18 of the periodic table. It has 8 valence electrons according to its group number.

Step 2: Calculate Total Valence Electrons

Oxygen (O) has 6 valence electrons. Since there are 3 oxygen atoms, the total number of valence electrons from oxygen is \(3 \times 6 = 18\). Adding these to xenon's valence electrons, we get a total of \(8 + 18 = 26\) valence electrons for \(\text{XeO}_3\).

Step 3: Predict the Geometry with VSEPR Theory

Using VSEPR theory, xenon being the central atom with 3 bonded oxygens and 1 lone pair (total of 4 regions of electron density) leads to a tetrahedral electron geometry. However, considering the presence of a lone pair, the actual molecular geometry is pyramidal.

Step 4: Identify the Molecular Geometry

Given the tetrahedral electron geometry and one lone pair, the structure of \(\text{XeO}_3\) is adjusted to accommodate lone pair repulsion effects, resulting in a pyramidal shape.

Key Concepts

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory is a helpful model for determining the shape of a molecule. It explains how the arrangement of electron pairs around an atom affects the geometry of the molecule. The basic premise of VSEPR Theory is that electron pairs will position themselves as far apart as possible from each other to minimize repulsion. This is because electron pairs are negatively charged and repel each other naturally.

In practice, VSEPR theory considers both bonding electron pairs (shared between atoms) and lone electron pairs (localized on a single atom). By counting these regions of electron density, one can predict the shape of a molecule.

• If a molecule has four regions of electron density, it may first assume a tetrahedral electron pair geometry.
• Notably, lone pairs take up more space than bonding pairs and can push the bonding pairs closer together.

Applying VSEPR theory helps chemists and students alike conceptualize the three-dimensional arrangement of atoms, as seen in compounds like Xenon Trioxide.

Valence Electrons

Understanding valence electrons is crucial for predicting how atoms interact in compounds. Valence electrons are the outermost electrons of an atom and are responsible for chemical bonding, as they can be lost, gained, or shared between atoms.

For example:

• Xenon, a noble gas, has 8 valence electrons, which is typical for elements in Group 18 of the periodic table.
• Oxygen, on the other hand, has 6 valence electrons, allowing it to form stable compounds by sharing electrons to fulfill the Octet Rule, which states that atoms prefer having eight electrons in their valence shell for stability.

When atoms form molecules, their valence electrons interact. In the case of \(\mathrm{XeO}_3\), the combination of valence electrons from xenon and three oxygen atoms gives us the total valence electron count needed to apply VSEPR Theory and deduce molecular geometry.

Recognizing how these electrons contribute to bonding and molecular shape is key to grasping the structural formation process of molecules.

Xenon Trioxide

Xenon Trioxide (\(\text{XeO}_3\)) is a fascinating compound due to its molecular geometry and the unique role of xenon as a central atom. Despite being a noble gas, xenon can form stable compounds with highly electronegative elements like oxygen.

In \( ext{XeO}_3\), the xenon atom is surrounded by three oxygen atoms, giving it a framework of bonds. The total number of valence electrons in \(\text{XeO}_3\) is 26, contributing to its unique shape.

• Xenon has 8 valence electrons.
• Each oxygen atom contributes 6 valence electrons, which adds up to 18 electrons for oxygen in total.

The arrangement of these electrons forms a three-dimensional shape that can initially appear tetrahedral if considering electron pairs only. However, the presence of one lone pair on xenon, which repels the bonded pairs, alters this shape to be pyramidal.

Understanding Xenon Trioxide helps illustrate how even noble gases, under certain conditions, can participate in bonding and molecular geometry deviations from expected norms.