Question

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

Short answer

The total number of lone pair electrons in \(\mathrm{XeOF}_{4}\) is 2 pairs.

Step-by-step solution

Determine the Total Valence Electrons

Xenon (Xe) belongs to group 18 and contributes 8 valence electrons. Oxygen (O) is in group 16 and contributes 6 valence electrons. Each of the four fluorine (F) atoms from group 17 contributes 7 valence electrons. Therefore, calculate the total valence electrons as follows:\[8 ( ext{Xe}) + 6 ( ext{O}) + 4 \times 7 ( ext{F}) = 42 \]

Form the Initial Bonds

Place Xenon (Xe) in the center as the central atom. Form a bond between Xe and each of the four fluorine atoms, and one bond between Xe and the oxygen atom. This forms five sigma bonds.

Deduct the Bonding Electrons

There are five sigma bonds, and each bond uses 2 electrons. Calculate the total number of electrons used in bonding:\[5 \times 2 = 10 \text{ electrons} \]

Calculate Remaining Electrons as Lone Pairs

Subtract the electrons used in bonding from the total number of valence electrons to find the remaining lone pair electrons:\[42 \text{ (total valence electrons)} - 10 \text{ (bonding electrons)} = 32 \text{ electrons} \]

Assign Lone Pairs to Complete Octets

Firstly, complete the octets of the outer atoms (Fluorine and Oxygen). There are four fluorine atoms, each needing 6 more electrons, totaling:\[ 4 \times 6 = 24 \text{ electrons}\]For oxygen, it needs 4 more electrons, totaling:\[ 4 \text{ electrons}\]Adding these, we use 28 electrons to complete the octets around the outer atoms.

Determine Lone Pairs on Xenon

After assigning 28 electrons to complete the octets of the outer atoms, calculate the electrons left:\[ 32 - 28 = 4 \text{ electrons} \]These 4 electrons remain as lone pairs on the central Xenon atom, forming 2 lone pairs.

Key concepts

Valence Electrons

Valence electrons play a crucial role in determining how atoms interact and bond with each other. They are the electrons found in the outermost shell of an atom. These are the electrons involved in forming chemical bonds.
Helium, for example, has only two valence electrons that fill its outer shell, while elements like chlorine have seven. More valence electrons typically mean the element is more reactive, as it can gain, lose, or share these electrons to achieve a full shell.
In the case of xenon ( Xe ), which belongs to group 18 of the periodic table, it has eight valence electrons. This is noteworthy since, unlike many noble gases, xenon can form compounds due to the available p orbitals allowing for bonding and lone pair configurations. Understanding valence electrons is the first step in figuring out the bonding and non-bonding interactions in a molecule.

Sigma Bonds

In the molecule XeOF_4 , sigma bonds are pivotal in holding the atoms together. A sigma bond ( σ-bond ) is the strongest type of covalent bond and is formed by the direct overlap of atomic orbitals.
Each bond involves two valence electrons, one from each atom participating in the bond. In XeOF_4 , xenon forms sigma bonds with four fluorine atoms and one oxygen atom, giving us five sigma bonds in total.

• These bonds primarily occur when s orbitals overlap with other s or p orbitals.
• The sigma bonds are directional bonds that lie along the axis connecting the two bonded nuclei.

Understanding sigma bonds is essential for understanding the structure and properties of complex molecules like xenon's compounds.

Octet Rule

The octet rule is a fundamental concept in chemistry that refers to the tendency of atoms to prefer having eight electrons in their valence shell. This rule stems from the stability observed in noble gases, which naturally have full valence shells.
In practice, atoms will gain, lose, or share electrons to fulfill their octet, which is evident in the case of XeOF_4 . Each fluorine atom, needing one electron to complete its octet, forms a single bond with xenon.
However, xenon itself deviates from this rule as it has more than an octet due to its ability to expand its valence shell, accommodating additional electrons beyond the typical eight. This capacity for expanded octets makes xenon unique among the noble gases.

• The octet rule helps explain the stable configurations of many molecules.
• Deviations, like those seen in xenon compounds, highlight the variability in chemical bonding.

Xenon Chemistry

Xenon chemistry is intriguing due to its rarity among noble gases forming compounds. While traditionally seen as inert, xenon can participate in chemical reactions under certain conditions due to its relatively large atomic size and available valence electrons.
The molecule XeOF_4 exemplifies xenon's ability to form stable compounds beyond the octet rule's limitations, including forming multiple bonds and accommodating lone pairs.
This behavior can be attributed to xenon's electron configuration, which allows for expanded orbitals capable of forming new bonds and locations for lone pairs. This flexibility is essential for its unique bonding capabilities.

• Xenon can form stable compounds with elements like oxygen and fluorine, as seen in XeOF_4 .
• Its chemical reactivity is a topic of study, revealing insights into the chemistry of other noble gases that might be less inert than previously thought.

Understanding xenon chemistry provides insight into the potential reactivity and bond formations of other heavier elements in the periodic table.