Problem 80 - A Complete Resource Book in Chemistry for JEE Main

Question

Total number of lone pair of electrons in \(\mathrm{XeOF}_{4}\) is (a) 0 (b) 1 (c) 2 (d) 3

Step-by-Step Solution

Answer

The total number of lone pair of electrons in \( \mathrm{XeOF}_{4} \) is 1.

Step 1: Identify the Valence Electrons of Xenon

The central atom in \( \mathrm{XeOF}_{4} \) is Xenon (\( \mathrm{Xe} \)). Xenon is a noble gas and is located in group 18 of the periodic table, so it has 8 valence electrons.

Step 2: Count the Electrons Used in Bonds

In \( \mathrm{XeOF}_{4} \), Xenon forms one double bond with Oxygen and four single bonds with Flourines. Each single bond takes 2 electrons and the double bond takes 4 electrons, resulting in \( 2 \times 4 + 4 = 12 \) electrons being used in bonding.

Step 3: Calculate Remaining Electrons on Xenon

Xenon starts with 8 valence electrons. After forming bonds, it has used 8 of its valence electrons (since bonds can be formed through shared electrons). However, since there are additional electrons needed for the bonds, the second part of step 2 accounts for that. Xenon might extend its octet to accommodate the extra bonding, and additional electrons might be coming from the fluorine and oxygen atoms.

Step 4: Determine Lone Pairs on Xenon

After accessing the original 8 electrons and considering \( Xe \) can have an expanded octet absorbing electrons, the computation of true lone pair electrons settles since fluorine needs electrons, some are freed as lone pairs on \( Xe \). After placing all electron pairs for bonding, \( Xe \) has a lone pair of electrons left. Therefore there is just \( 1 \) lone pair.

Key Concepts

Molecular Geometry of XeOF4

The molecular geometry of a molecule like XeOF4 is crucial for understanding its physical and chemical properties. The shape or geometric structure of XeOF4 can be described as square pyramidal. This configuration arises due to the arrangement of electron pairs around the central xenon atom. The placement of bonds and lone pairs shape the overall geometry of a molecule, influencing its reactivity and interactions with other substances.
The square pyramidal geometry in XeOF4 is due to:

• One lone pair: This lone pair occupies one position, causing an imbalance leading to the pyramidal structure.
• Four Xe-F bonds: Arranged in a plane forming the square base of the pyramid.
• One Xe-O bond: Positioned at the apex of the pyramid.

Understanding molecular geometry helps in predicting intermolecular forces and behavior in various chemical processes.

Valence Electrons

Valence electrons are the outermost electrons in an atom and are key players in chemical bonding. For xenon in XeOF4, these are the eight electrons located in the outer shell. These electrons are crucial as they determine how atoms interact and bind with each other.
When analyzing a molecule like XeOF4:

• Xenon, the central atom, begins with eight valence electrons.
• Electrons are shared or transferred during bond formation.
• The resulting distribution of these electrons determines the molecule's overall structure and stability.

Valence electrons essentially dictate the bonding capabilities and limitations of an atom, which in turn defines chemical compounds' properties and behaviors.

Expanded Octet

The concept of the expanded octet is sometimes challenging because it defies the traditional octet rule most substances typically follow. Elements in periods 3 and below on the periodic table, like xenon, are capable of having more than eight electrons in their valence shell.
For XeOF4:

• Xenon extends its capacity to hold additional electrons beyond the typical octet (8 electrons) to facilitate bonding.
• This capability allows the formation of more complex molecules with different geometrical arrangements.
• Such structures may include more bonds than a single typical octet can accommodate, thus leading to molecules like XeOF4.

This flexibility in xenon’s electron configuration allows it to participate in rich chemistry, forming bonds with multiple atoms and incorporating lone pairs.

Chemical Bonding

Chemical bonding refers to the interactions that hold atoms together in molecules. In XeOF4, different types of bonds and electron interactions come into play to form the complete structure.
Diving into the bond types in XeOF4:

• Double bond: Between xenon and oxygen, resulting from the sharing of two pairs of electrons.
• Single bonds: Four such bonds between xenon and fluorine atoms, sharing one pair of electrons in each bond.
• Lone pair interactions: While bonds occupy space, lone pairs on xenon subtly influence the geometry and stability of the molecule.

Chemical bonding principles explain molecule formation, revealing how atoms share or transfer electrons to achieve stable configurations. Hence, understanding the nuances of bonding is necessary for grasping broader chemical behaviors.