Problem 18 - Chemistry in 30 days

Question

Of the following sets, which does not contain isoelectronic species? (a) \(\mathrm{PO}_{4}^{3}, \mathrm{SO}_{4}^{2}, \mathrm{ClO}_{4}-\) (b) \(\mathrm{CN}^{-}, \mathrm{N}_{2}, \mathrm{C}_{2}^{2-}\) (c) \(\mathrm{SO}_{3}^{2-}, \mathrm{CO}_{3}^{2-}, \mathrm{NO}_{3}^{-}\) (d) \(\mathrm{BO}_{3}^{3}, \mathrm{CO}_{3}^{2-}, \mathrm{NO}_{3}^{-}\)

Step-by-Step Solution

Answer

Set (c) does not contain isoelectronic species.

Step 1: Understand Isoelectronic Species

Isoelectronic species are different atoms, ions, or molecules that have the same number of electrons. To determine whether the given sets contain isoelectronic species, we need to count and compare the total number of electrons in each species within the set.

Step 2: Calculate Electrons in Set (a)

For each species, add up the electrons: - PO extsubscript{4} extsuperscript{3-}: P = 15, O extsubscript{4} = 32 (four O atoms), and 3 extra electrons for the 3- charge, totaling 50 electrons. - SO extsubscript{4} extsuperscript{2-}: S = 16, O extsubscript{4} = 32, and 2 extra, totaling 50 electrons. - ClO extsubscript{4} extsuperscript{-}: Cl = 17, O extsubscript{4} = 32, and 1 extra, totaling 50 electrons. All have 50 electrons.

Step 3: Calculate Electrons in Set (b)

For each species, count: - CN extsuperscript{-}: C = 6, N = 7, and 1 extra, totaling 14 electrons. - N extsubscript{2}: N = 7 for each, so 14 electrons total. - C extsubscript{2} extsuperscript{2-}: C = 6 for each, plus 2 extra, totaling 14 electrons. All have 14 electrons.

Step 4: Calculate Electrons in Set (c)

For each species, count: - SO extsubscript{3} extsuperscript{2-}: S = 16, O extsubscript{3} = 24, and 2 extra, totaling 42 electrons. - CO extsubscript{3} extsuperscript{2-}: C = 6, O extsubscript{3} = 24, and 2 extra, totaling 32 electrons. - NO extsubscript{3} extsuperscript{-}: N = 7, O extsubscript{3} = 24, and 1 extra, totaling 32 electrons. 32 electrons for two species, 42 for the other.

Step 5: Calculate Electrons in Set (d)

For each species, count: - BO extsubscript{3} extsuperscript{3-}: B = 5, O extsubscript{3} = 24, and 3 extra, totaling 32 electrons. - CO extsubscript{3} extsuperscript{2-}: C = 6, O extsubscript{3} = 24, and 2 extra, totaling 32 electrons. - NO extsubscript{3} extsuperscript{-}: N = 7, O extsubscript{3} = 24, and 1 extra, totaling 32 electrons. All have 32 electrons.

Step 6: Determine the Set without Isoelectronic Species

Sets (a), (b), and (d) have members with identical electron counts, meaning they contain isoelectronic species. However, Set (c) has species with differing electron numbers (32 and 42), meaning it does not contain isoelectronic species.

Key Concepts

Electron Calculation

Calculating the number of electrons in molecular species is fundamental to understanding if they are isoelectronic. Isoelectronic species, by definition, have the same number of electrons. Calculating the electrons requires considering the atomic numbers of constituent atoms and any extra electrons due to molecular charges.
This process involves identifying each element's atomic number, multiplying by the number of each type of atom, and adding or subtracting electron numbers based on the ionic charge:

• For neutral atoms, use the atomic number.
• For ions, adjust by adding electrons if the charge is negative, or subtracting for positive charges.

In practice, for a set of species, each must yield the same electron total to be considered isoelectronic. This exercise is valuable for grasping molecular stability and interactions in chemistry.

Molecular Ions

Molecular ions are molecules that have gained or lost electrons, resulting in a net positive or negative charge. The ionization process impacts the total electron count of molecules. Understanding how ions form and their impact on electron count is essential in chemistry.
Molecular ions are key in:

• Determining electron configurations and molecular stability.
• Predicting chemical behavior and reactions.
• Explaining properties such as solubility and electrical conductivity.

Despite the changes in electron numbers due to ionic charges, molecules that are isoelectronic usually exhibit similar chemical properties. This assumption simplifies many chemical reactions and compound predictions.

Charge Effects on Electrons

Charges play a significant role in how electrons are counted and influence the behavior of an ion. Negative charges indicate extra electrons, while positive charges mean fewer electrons. Understanding these effects is crucial for accurately determining electron count in molecules and ions.
When assessing isoelectronic species, it's important to:

• Accurately calculate changes in electron numbers due to charges.
• Understand that similar electron counts can lead to similar chemical behaviors despite differences in charges.
• Recognize the structural and reactivity implications of electron changes.

Charge considerations are vital when predicting and rationalizing chemical phenomena and reactions in molecular chemistry.

Chemistry Education

Grasping concepts such as isoelectronic species is a foundational aspect of chemistry education. It involves learning how to calculate and interpret electron distributions in atoms, ions, and molecules.
To facilitate chemistry learning, focus on:

• Using visual aids and models to represent atomic and molecular structures.
• Practicing electron counting regularly to enhance accuracy and confidence.
• Encouraging inquiry and problem-solving to develop deeper understanding.

Understanding isoelectronic relationships enhances knowledge about molecular stability, reactions, and properties, which are core to both basic chemistry principles and advanced applications like drug design and materials science.