Problem 164 - Chemistry: An Atoms-Focused Approach

Question

How many pairs of electrons does xenon share in the following molecules and ions? (a) \(\mathrm{XeF}_{2} ;\) (b) \(\mathrm{XeOF}_{2}\) (c) \(\mathrm{XeF}^{+} ;\) (d) \(\mathrm{XeF}_{5}^{+} ;\) (e) \(\mathrm{XeO}_{4}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{XeF}_{2}\) (b) \(\mathrm{XeOF}_{2}\) (c) \(\mathrm{XeF}^{+}\) (d) \(\mathrm{XeF}_{5}^{+}\) (e) \(\mathrm{XeO}_{4}\) Answer: (a) 2 electron pairs (b) 3 electron pairs (c) 1 electron pair (d) 5 electron pairs (e) 4 electron pairs

Step 1: Understand the concept of covalent bonds and electron pairs

A covalent bond is a chemical bond between two atoms that share one or more pairs of electrons. In this case, we need to look at the shared electrons between the xenon atom and its bonding atoms in each molecule or ion. Each covalent bond counts as one shared electron pair.

Step 2: Draw the Lewis structure for each molecule or ion

For each of the molecules or ions provided, draw the Lewis structure to visualize the bonding between atoms. The Lewis structure represents valence electrons as dots and covalent bonds as lines. (a) \(\mathrm{XeF}_{2}\) (b) \(\mathrm{XeOF}_{2}\) (c) \(\mathrm{XeF}^{+}\) (d) \(\mathrm{XeF}_{5}^{+}\) (e) \(\mathrm{XeO}_{4}\)

Step 3: Count the number of shared electron pairs involving xenon

For each molecule or ion, count the number of covalent bonds or lines connecting the xenon atom to other atoms. These represent the number of shared electron pairs. (a) \(\mathrm{XeF}_{2}\): Xenon has two covalent bonds with two fluorine atoms, so it shares 2 electron pairs. (b) \(\mathrm{XeOF}_{2}\): Xenon has two covalent bonds with two fluorine atoms and another bond with an oxygen atom, so it shares 3 electron pairs. (c) \(\mathrm{XeF}^{+}\): Xenon has one covalent bond with one fluorine atom, so it shares 1 electron pair. (d) \(\mathrm{XeF}_{5}^{+}\): Xenon has five covalent bonds with five fluorine atoms, so it shares 5 electron pairs. (e) \(\mathrm{XeO}_{4}\): Xenon has four covalent bonds with four oxygen atoms, so it shares 4 electron pairs.

Step 4: Summary

Based on analyzing the Lewis structure of the given molecules and ions, we have found the following number of shared electron pairs for xenon: (a) \(\mathrm{XeF}_{2}\): 2 electron pairs (b) \(\mathrm{XeOF}_{2}\): 3 electron pairs (c) \(\mathrm{XeF}^{+}\): 1 electron pair (d) \(\mathrm{XeF}_{5}^{+}\): 5 electron pairs (e) \(\mathrm{XeO}_{4}\): 4 electron pairs

Key Concepts

Lewis Structures

Lewis structures are diagrams used to show the bonding between atoms of a molecule and the lone pairs of electrons that may exist. The valence electrons, which are the outermost electrons of an atom, are represented as dots. Typically, bonding pairs of electrons are shared between atoms and represented as lines. The main goal of constructing a Lewis structure is to satisfy the octet rule for each atom, meaning they should be surrounded by eight electrons, giving them the same electron configuration as a noble gas. However, Xenon (Xe) can have expanded octets due to its larger size and ability to hold more electrons.
To draw a Lewis structure, follow these steps:

• Count the total number of valence electrons in the molecule or ion.
• Write the skeletal structure by connecting atoms with single bonds.
• Complete the octet of outer atoms, then place the remaining electrons on the central atom.
• If the central atom lacks an octet, form double or triple bonds as necessary.

Lewis structures help in visualizing electron pair distributions and predicting molecule shapes.

Shared Electron Pairs

Shared electron pairs are a fundamental concept in covalent bonding. They refer to pairs of valence electrons shared between two atoms, resulting in a stable balance of attractive and repulsive forces that hold the atoms together in a molecule. For instance, in the molecule \( \mathrm{XeF}_2 \), xenon shares one electron pair with each of the two fluorine atoms. This sharing of electron pairs allows each atom to attain a more stable electron configuration, often resembling the nearest noble gas.
Here's how shared electron pairs work:

• Single bonds involve one shared electron pair and are represented by a single line between two atoms.
• Double bonds involve two shared electron pairs, represented by two lines.
• Triple bonds involve three shared electron pairs, represented by three lines.

Shared electron pairs are key to understanding molecular structures and chemical interactions.

Xenon Compounds

Xenon compounds are fascinating due to xenon's ability to form bonds, despite being a noble gas, which typically do not form compounds easily. Xenon can participate in chemical reactions under certain conditions, leading to the formation of various fluorides and oxo compounds. Examples include \( \mathrm{XeF}_2 \), where xenon is bonded to fluorine, and \( \mathrm{XeO}_4 \), where xenon is bonded to oxygen.
Key points about xenon compounds:

• Xenon forms stable compounds mainly with highly electronegative elements like fluorine and oxygen.
• These compounds often have unusual oxidation states for xenon, showcasing its ability to expand its octet.
• Xenon compounds such as \( \mathrm{XeF}_4 \) and \( \mathrm{XeO}_3 \) are used for research in fields like chemistry and materials science.

Understanding xenon compounds provides insight into the behavior of noble gases under unusual circumstances.