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

Question

Match the following: List I (Compound) List II (Number of lone pair electron) 1\. \(\mathrm{XeF}_{2}\) (i) 0 2\. \(\mathrm{XeF}_{4}\) (ii) 1 3\. \(\mathrm{XeF}_{6}\) (iii) 2 4\. \(\mathrm{XeO}_{3}\) (iv) 3 The correct matching is: \(\begin{array}{llll}1 & 2 & 3 & 4\end{array}\) (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 matching is option (d): 1-(iv), 2-(iii), 3-(ii), 4-(i).

Step 1: Determine Lone Pairs for XeF2

In the compound \( \text{XeF}_2 \), xenon is the central atom. Xe typically forms 8-electron structures, having 2 bonds with fluorine and a total of 10 valence electrons. Subtract 4 electrons used in bonds; 6 electrons remain, forming 3 lone pairs. Therefore, Match 1 to (iv).

Step 2: Determine Lone Pairs for XeF4

In \( \text{XeF}_4 \), xenon forms 4 bonds using 8 electrons, with 6 electrons from 4 bonds with each fluorine atom. Total valence electrons minus bonding electrons (12 - 8) leaves us with 4, making 2 lone pairs. Match 2 to (iii).

Step 3: Determine Lone Pairs for XeF6

For \( \text{XeF}_6 \), xenon is bonded to 6 fluorine atoms, using all 12 valence electrons as bonds (6 pairs) and 2 electrons forming 1 remaining lone pair. Match 3 to (ii).

Step 4: Determine Lone Pairs for XeO3

In \( \text{XeO}_3 \), xenon bonds to 3 oxygen atoms (6 electrons in bonds), and no electrons remain unpaired, indicating 0 lone pairs. Match 4 to (i).

Step 5: Matching the List

The matching results in: 1 matches (iv), 2 matches (iii), 3 matches (ii), and 4 matches (i). This corresponds to option (d).

Key Concepts

Lone Pairs

In chemistry, lone pairs are crucial when understanding the spatial arrangement of molecules. Lone pairs refer to valence electrons in an atom that are not shared with another atom. These electrons occupy space around the atom and significantly influence the molecule's shape and properties.

For many compounds, especially xenon compounds, identifying the number of lone pairs can help predict molecular geometry. In the compound \( \text{XeF}_2 \), xenon has three lone pairs, which means it retains three pairs of electrons not involved in bonding.

This leads to its linear shape as non-bonding electrons push the bonded electrons into a straight line.

• 3 lone pairs in \( \text{XeF}_2 \)
• 2 lone pairs in \( \text{XeF}_4 \) result in a square planar shape
• 1 lone pair in \( \text{XeF}_6 \) results in a distorted octahedral shape
• No lone pairs in \( \text{XeO}_3 \), giving a trigonal pyramidal shape

The non-bonding electrons, although invisible, cause these changes in geometry making them vital for structural understanding.

Xenon Compounds

Xenon is typically known as an inert or noble gas, but under specific conditions, it can form stable compounds. Xenon compounds, such as \( \text{XeF}_2 \), \( \text{XeF}_4 \), and \( \text{XeF}_6 \), involve xenon bonding with more electronegative elements.

Xenon makes these compounds by expanding its octet, which means it can hold more than 8 electrons in its valence shell. This quality allows xenon to participate in chemical reactions. For instance:

• \( \text{XeF}_2 \): A linear molecule owing to its electron configuration creating a stable molecule ideal for various reactions.
• \( \text{XeF}_4 \): A square planar molecule, which is symmetric and adds stability to xenon's unusual chemistry.
• \( \text{XeF}_6 \): Displays a more complex geometry because of xenon's flexibility in accommodating numerous electrons.

Understanding how xenon behaves and forms these compounds unveils not only xenon's chemistry but the broader concept of chemical bonding beyond the classic octet rule.

Valence Electrons

Valence electrons play a significant role in determining how atoms bond and interact with one another. These are the outermost electrons in an atom and are crucial in forming chemical bonds.

In the context of xenon compounds, it's important to know how many valence electrons xenon might have. Xenon typically possesses eight valence electrons. However, during the formation of compounds like \( \text{XeF}_2 \), \( \text{XeF}_4 \), and \( \text{XeF}_6 \), xenon can utilize additional electrons from bonded atoms.

• In \( \text{XeF}_2 \): Xenon uses 4 of its 8 valence electrons for bonding, leaving it with 3 lone pairs.
• For \( \text{XeF}_4 \): Xenon utilizes 8 electrons for bonding, resulting in 2 lone pairs.
• With \( \text{XeF}_6 \): Xenon uses all 12 electrons for forming bonds, resulting in 1 lone pair.

As a noble gas, xenon's ability to expand its octet and make use of these electrons challenges typical bonding models and showcases the complexity of chemical interactions.