Problem 147 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one the following sets of ions represents the collection of isoelectronic species? (a) \(\mathrm{Na}^{+}, \mathrm{Ca}^{2+}, \mathrm{Sc}^{3+}, \mathrm{F}-\) (b) \(\mathrm{K}^{+}, \mathrm{Cl}^{-}, \mathrm{Mg}^{2+}, \mathrm{Sc}^{3+}\) (c) \(\mathrm{K}^{+}, \mathrm{Ca}^{2+}, \mathrm{Sc}^{3+}, \mathrm{Cl}^{-}\) (d) \(\mathrm{Na}^{+}, \mathrm{Mg}^{2+}, \mathrm{Al}^{3+}, \mathrm{Cl}-\)

Step-by-Step Solution

Answer

The isoelectronic set is option (d): \(\mathrm{Na}^+, \mathrm{Mg}^{2+}, \mathrm{Al}^{3+}\).

Step 1: Understand Isoelectronic Species

Isoelectronic species are atoms, ions, or molecules that have the same number of electrons. For ions in particular, we must account for the electrons lost or gained due to the charge.

Step 2: Determine Electron Counts

We find the number of electrons for each ion:- \(\mathrm{Na}^+\): Sodium normally has 11 electrons; losing one electron gives 10.- \(\mathrm{Mg}^{2+}\): Magnesium normally has 12 electrons; losing two electrons gives 10.- \(\mathrm{Al}^{3+}\): Aluminum normally has 13 electrons; losing three electrons gives 10.- \(\mathrm{Cl}^-\): Chlorine normally has 17 electrons; gaining one electron gives 18.Similarly for the other options.

Step 3: Compare Electron Numbers

We'll focus on which species have the same number of electrons. Option (d), \(\mathrm{Na}^+\), \(\mathrm{Mg}^{2+}\), and \(\mathrm{Al}^{3+}\) all have 10 electrons, whereas \(\mathrm{Cl}^-\) has 18 electrons. Other options do not have a group where all have the same electron count.

Step 4: Identify the Isoelectronic Set

Among the options, (d) \(\mathrm{Na}^{+}, \mathrm{Mg}^{2+}, \mathrm{Al}^{3+}\) have the same number of electrons (10 electrons each). Although \(\mathrm{Cl}^-\) has a different count, the rest form an isoelectronic set. Thus, this is the correct choice.

Key Concepts

Electron Configuration

Electron configuration refers to the distribution of electrons in an atom or ion. Electrons are arranged around the nucleus in various energy levels or shells. The configuration is determined by the specific order in which these electrons fill available orbital spaces. Understanding electron configuration helps us predict an element's chemical properties and reactivity.
Electrons fill orbitals starting from the lowest energy level, following the rules of the Aufbau principle, Hund's Rule, and the Pauli Exclusion Principle.

• The Aufbau principle states that electrons occupy the lowest available energy orbital.
• Hund's Rule asserts that electrons will fill orbitals singly before pairing up in any single orbital.
• The Pauli Exclusion Principle dictates that no two electrons can have the same set of quantum numbers within the same atom.

Understanding these principles is crucial since they form the backbone of the electron configuration description, which is foundational for grasping concepts like isoelectronic species.

Ions

Ions are atoms or molecules that have gained or lost one or more electrons. This gain or loss results in a net electric charge, either positive or negative.
In chemistry, ions form through the transfer of electrons. When an atom loses an electron, it becomes a positively charged ion or cation. Conversely, when an atom gains an electron, it becomes a negatively charged ion or anion. For example:

• Na (+1) ion is formed when a sodium atom loses one electron.
• Cl (-1) ion is created when a chlorine atom gains an electron.

Ions are central to learning about chemical reactions because they interact and react differently than neutral atoms. By understanding the charge and behavior of ions, students can predict the outcomes of many chemical reactions and understand concepts like isoelectronic species.

Charge

The concept of charge is fundamental in chemistry and refers to the electrical charge an ion carries after gaining or losing electrons. The charge is often displayed as a superscript followed by the element symbol, such as \(Na^{+}\) or \(Cl^{-}\).
An atom's charge depends on the balance between the number of protons, which are positive, and electrons, which are negative. Losing electrons results in a positive charge, leading to a cation, whereas gaining electrons leads to a negative charge, forming an anion.

• Positive Charge (Cation): Fewer electrons than protons.
• Negative Charge (Anion): More electrons than protons.

Charge is essential because it influences how ions will interact within chemical processes. This understanding helps students know what to examine when determining isoelectronic species, which share the same electron count but not necessarily charge.

Chemistry Fundamentals

Chemistry fundamentals lay the foundation for many concepts, including electron configuration, ions, and charges. Together, they help describe the behavior of atoms and molecules in different environments.
Isoelectronic species, a key concept in the context of chemistry fundamentals, are collections of atoms or ions that have equal numbers of electrons. Understanding this requires a grasp of electron gain and loss, the resulting formation of ions, and the determination of electron configurations.
The process used to identify such groups involves:

• Counting electrons in each ion.
• Determining what changes occur in electron configuration as a result of ionization.
• Identifying species with equivalent electron counts.

This knowledge not only enhances problem-solving skills in chemistry but also broadens the understanding of atomic structure and electron interplay across different substances.