Problem 174 - A Complete Resource Book in Chemistry for JEE Main

Question

How many lone pairs are there at xenon in XeOF \(_{4} ?\)

Step-by-Step Solution

Answer

Xenon in XeOF \(_4\) has 1 lone pair of electrons.

Step 1: Determine the Valence Electrons

Xenon (Xe) belongs to Group 18 of the periodic table, which means it has 8 valence electrons. Oxygen (O) contributes 6 electrons, and each of the 4 fluorine (F) atoms contributes 7 electrons, making a total of \(8 + 6 + (4 \times 7) = 42\) valence electrons for XeOF \(_4\).

Step 2: Allocate Electrons to Bonds

First, connect the central xenon atom to the surrounding atoms: one oxygen and four fluorine atoms. Each bond primarily uses two electrons, so the five bonds use \(5 \times 2 = 10\) electrons.

Step 3: Distribute Remaining Electrons to Atoms

There are \(42 - 10 = 32\) electrons left after forming bonds. The remaining electrons are distributed to satisfy the octet rule, primarily around the oxygen and fluorine atoms, as these typically follow the octet rule. This leaves xenon to potentially have any spare lone pairs.

Step 4: Observe Xenon's Octet Extension

Xenon can accommodate more than an octet due to available d-orbitals. After distributing electrons to ensure filling surrounding atoms (16 electrons to four fluorines and 6 to oxygen, totaling 22 electrons), 6 electrons remain that could be used to complete xenon's needs.

Step 5: Count Lone Pairs on Xenon

After using the remaining electrons, xenon will have a lone pair of electrons beyond the single bonds it has formed in this molecule. Thus, xenon in XeOF \(_4\) contains 1 lone pair of electrons.

Key Concepts

Lone Pairs

In the realm of chemistry, lone pairs are non-bonded pairs of electrons residing around an atom. Unlike those electrons that form bonds by sharing between atoms, lone pairs belong solely to one atom.
This distinction is critical as lone pairs significantly impact the shape and properties of molecules.
Let's break it down further:

• Lone pairs occupy more space around an atom than bonding pairs. This is due to their lack of a partner atom pulling them in another direction.
• Lone pairs cause distortion in the usual geometry of atoms, impacting the angles between bonds.
• They are crucial in determining the reactivity and polarity of molecules.

For instance, in XeOF  oxeON, the lone pair on xenon plays a vital role. It alters the molecular shape by repelling bonded electrons, making the molecule take a specific configuration. These insights display the importance of accounting for lone pairs when considering molecular structure and behavior.

Octet Rule

The octet rule is an essential guideline in molecular chemistry. It postulates that atoms tend to bond in such a way that each has eight electrons in their outer shell, much like the electron configuration of a noble gas.
However, the octet rule has its exceptions, and understanding these can clarify many molecular structures.

• Some elements, like hydrogen, are satisfied with two electrons (a duet).
• Metals such as beryllium and boron often have less than eight electrons.
• Elements that have access to d-orbitals, such as xenon, can hold more than eight electrons, a concept known as an 'expanded octet.'

XeOF  oxeON illustrates the expanded octet exception, where xenon, as the central atom, has more than eight electrons involved in bonding and lone pairs. Recognizing these exceptions is essential for accurately predicting and understanding molecule formation.

Electron Distribution

Electron distribution refers to the way electrons are arranged around atoms in a molecule. This distribution is fundamental to understanding how molecules bond and interact.
Electrons reside in different layers or shells, usually filling up space from the innermost to the outermost.

• Valence electrons are the electrons that occupy the outermost shell and are the most involved in chemical reactions.
• Bonding electrons are those that form ionic or covalent bonds by being shared or exchanged.
• Lone pairs are the non-bonding electrons remaining after bonds form.

For a compound like XeOF  oxeON, precise electron distribution helps predict its structure and function. In this molecule, electron distribution goes beyond typical bonds, with electrons shared unevenly among atoms and some remaining as lone pairs on xenon. Understanding electron distribution hence aids in predicting chemical behavior and geometry.

Xenon Compounds

Xenon compounds are fascinating exemplars of chemistry's surprises. Despite being a noble gas, xenon forms compounds due to its ability to expand its valence shell.
These compounds shed light on stability and reactivity challenges in seemingly inert elements.

• Xenon can undergo reactions with strong oxidizing agents due to its capacity for expanded valence shells.
• Common compounds include xenon fluorides and oxides, each demonstrating unique bonding characteristics.
• In compounds like XeOF  oxeON, xenon bonds with electronegative elements such as oxygen and fluorine, where its expanded octet plays a critical role.

These xenon compounds enhance our understanding of chemical bonding, especially pertaining to noble gases, and challenge our perceptions of inertness. They highlight the fascinating complexity and adaptability of elements when subject to varying conditions.