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

Step-by-Step Solution

Answer

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

Step 1: Understand the Molecular Formula

The given molecule is \( \mathrm{XeO}_3 \). This molecule is composed of one xenon (Xe) atom and three oxygen (O) atoms.

Step 2: Determine the Electron Geometry Using VSEPR

Use the Valence Shell Electron Pair Repulsion (VSEPR) theory to determine the geometry. Xenon has 8 valence electrons. In \( \mathrm{XeO}_3 \), xenon is bonded to three oxygens. Assuming each bond uses 2 electrons, 6 electrons are used in bonding, leaving 2 electrons as a lone pair on xenon.

Step 3: Assess the Molecular Geometry

With three bonded atoms (O) and one lone pair, the geometry around xenon is based on a tetrahedral electron geometry. However, the presence of the lone pair changes the observed molecular geometry to be trigonal pyramidal.

Step 4: Compare with Given Options

Review the options provided: (a) linear, (b) planar, (c) pyramidal, and (d) T-shaped. "Pyramidal" best fits the geometry of \( \mathrm{XeO}_3 \) given the lone pair causing the other atoms to assume a trigonal pyramidal shape.

Key Concepts

Molecular Geometry and Its Importance

Molecular geometry is all about the three-dimensional arrangement of atoms within a molecule. It significantly influences the chemical properties and behavior of the molecule. Molecules adopt specific shapes to minimize repulsion between electron pairs according to the Valence Shell Electron Pair Repulsion (VSEPR) theory.

This can affect everything from the molecule's reactivity to its color, and even its smell. Therefore, understanding molecular geometry allows chemists to predict how molecules will interact with each other.

• Geometry determines angles between bonds.
• It explains molecular polarity, which impacts reactivity.
• This knowledge aids in predicting molecular interactions with other compounds.

The molecular geometry of a molecule like xenon trioxide ( XeO_3 ) is deduced through analyzing both bonding pairs and lone pairs of electrons around the central atom, in this case, xenon (Xe). This analysis helps us determine exactly what shape the molecule takes.

The Role of Electron Pairs in VSEPR Theory

Electron pairs, including both bonding and lone pairs, play a crucial role in determining the molecular geometry of a compound through the VSEPR theory.

Bonding pairs are shared between atoms within a molecule, while lone pairs are not shared and remain on a single atom.

Lone pairs occupy more space than bonding pairs because they are not attracted to any other nucleus. This can distort molecular geometry by pushing the bonded atoms closer together.

• Bonding pairs participate directly in chemical bonds.
• Lone pairs repel more strongly than bonding pairs.
• The arrangement seeks to minimize total repulsion among all electron pairs.

In XeO_3 , electron pairs result in a pyramidal shape. The strong repulsion by the lone pairs forces the bonds with oxygen atoms to position themselves away from the lone pairs, creating a slightly compressed geometry.

Understanding the Xenon Trioxide Structure

Xenon trioxide ( XeO_3 ) is a fascinating molecule due to its arrangement and the properties of xenon as a noble gas.

Despite xenon being a noble gas, it can form compounds, and XeO_3 is one example. The molecule is composed of one xenon atom and three oxygen atoms bonded together, with xenon at the center.

Applying VSEPR theory, xenon holds three bonded pairs and one lone pair, which leads to a tetrahedral electronic geometry. However, this lone pair modifies the observed shape, giving XeO_3 its distinctive pyramidal shape.

• The geometry results in an asymmetrical shape.
• This structure exhibits polarity due to the uneven distribution of electrons.
• Prediction of interactions with other molecules involves understanding this altered shape.

Xenon trioxide’s unique structure and configuration showcases how seemingly inert elements can form reactive compounds under the right conditions.