Problem 156 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List I (Compound) 1\. \(\mathrm{XeF}_{2}\) 2\. \(\mathrm{XeF}_{4}^{\circ}\) 3\. \(\mathrm{XeF}_{6}\) 4\. \(\mathrm{XeO}_{3}\) List II (Number of lone pair electron) (i) 0 (ii) 1 (iii) 2 (iv) 3 The correct matching is: 1 2 3 4 (a) (iii) (iv) (ii) (ii) (b) (iv) (iii) (ii) (ii) (c) (iv) (ii) (ii) (iii) (d) (iv) (iii) (i) (ii)

Step-by-Step Solution

Answer

The correct match is (b) - (iv), (iii), (ii), (ii).

Step 1: Identify XeF2 and Lone Pairs

For XeF2, we determine its Lewis structure. Xenon (Xe) is in Group 18, so it has 8 valence electrons, while Fluorine (F) has 7 valence electrons each. XeF2 has a total of 22 valence electrons (8 from Xe and 14 from two F atoms). When arranging them with a stable electron configuration, XeF2 forms a Linear shape with 3 lone pairs on Xe, hence matching with number of lone pairs from List II as (iv) 3.

Step 2: Identify XeF4 and Lone Pairs

XeF4 also requires a Lewis structure for determination. Xe(8 valence electrons) and four F atoms (7 each) result in 36 valence electrons in XeF4. The structure equilibrates with a square planar geometry, placing 2 lone pairs on Xe. This pairs with (iii) 2 from List II.

Step 3: Identify XeF6 and Lone Pairs

Forming the Lewis structure for XeF6, we have Xe with 8 valence electrons, and 6 fluorine atoms contributing 42 electrons in total. An octahedral shape accommodates the lone pair arrangement for Xenon in this compound, resulting in 1 lone pair. Hence it matches with (ii) 1 from List II.

Step 4: Identify XeO3 and Lone Pairs

For XeO3, Xe has 8 valence electrons, with each O adding 6 electrons, totalling 26 valence electrons. The structure aligns with a pyramidal shape, explaining the presence of 1 lone pair on Xe, consistent with (ii) 1 from List II.

Key Concepts

Lewis Structures

Lewis Structures are essential for understanding how atoms in a molecule are bonded and how electrons are arranged around them. It’s a visual representation of the valence electrons that helps us predict molecular shapes and properties.

• Each atom is represented by its symbol.
• Valence electrons of the atom are shown as dots around the symbol. These electrons are in the outermost shell and are the ones involved in bonding.
• Lines represent covalent bonds, showing shared pairs of electrons between atoms.

To draw a Lewis structure, count the total number of valence electrons in a molecule, arrange them to satisfy the octet rule (where possible), and assign lone pairs or bond pairs as needed. For Xenon fluoride compounds like \( \text{XeF}_2 \), \( \text{XeF}_4 \), and \( \text{XeF}_6 \), this method helps disclose how Xenon can have more than eight electrons surrounding it through "expanded octet" property.

Lone Pair Electrons

Lone pair electrons, also known as non-bonding pairs, are valence electrons that are not shared with another atom and do not participate in bonding. They influence molecular geometry and reactivity.

• Present on atoms to satisfy the octet rule when there aren't enough atoms to form bonds.
• Their presence can repel bonding pairs, impacting the geometry of the molecule.

For example, in \( \text{XeF}_2 \), Xenon has three lone pairs. These pairs contribute to the \( \text{linear geometry} \) of the molecule by pushing the bonded pairs of electrons into alignment. Understanding where lone pairs are present aids in predicting and explaining the molecular behavior and geometry.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are critical in determining how atoms bond and react with each other. They participate in forming chemical bonds either by sharing, losing, or gaining electrons.

• Group number of elements can help in determining the number of valence electrons in main group elements.
• Generally range from 1 to 8 for main group elements.

In the Xenon compounds from our exercise, Xenon's valence electrons are crucial in forming bonds with fluorine and oxygen. For example, in \( \text{XeF}_4 \), each fluorine atom requires one electron to attain stability, making Xenon's \( 8 \) valence electrons pivotal in accommodating a stable bond structure.

Molecular Geometry

Molecular Geometry describes the three-dimensional arrangement of atoms within a molecule. It provides insight into molecular shape and its potential interactions with other molecules.

• Determined by the number of bonding pairs and lone pairs on the central atom.
• Common geometries include linear, bent, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral.

For instance, \( \text{XeF}_2 \) has a linear geometry due to three lone pairs on Xenon pushing the bonded pairs apart. Similarly, \( \text{XeF}_4 \) has a square planar shape thanks to its two lone pairs setting the arrangement on a flat plane. These spatial arrangements are paramount in predicting the reactivity and interaction of molecules.