Problem 24 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The group having isoelectronic species is: (a) \(\mathrm{O}^{2-}, \mathrm{F}^{-}, \mathrm{Na}^{+}, \mathrm{Mg}^{2+}\) (b) \(\mathrm{O}^{-}, \mathrm{F}^{-}, \mathrm{Na}, \mathrm{Mg}^{+}\) (c) \(\mathrm{O}^{2-}, \mathrm{F}^{-}, \mathrm{Na}, \mathrm{Mg}^{2+}\) (d) \(\mathrm{O}^{-}, \mathrm{F}^{-}, \mathrm{Na}^{+}, \mathrm{Mg}^{2+}\)

Step-by-Step Solution

Answer

The group in option (a) is isoelectronic, with each species having 10 electrons.

Step 1: Define Isoelectronic Species

Isoelectronic species are atoms or ions that have the same number of electrons. This means they share the same electronic structure and often have similar chemical properties.

Step 2: Determine Electrons for Each Ion in Option (a)

- \(\text{O}^{2-}\): Oxygen normally has 8 electrons. With a \(2-\) charge, it has gained 2 additional electrons, for a total of 10.- \(\text{F}^{-}\): Fluorine normally has 9 electrons. With a \(-1\) charge, it has gained 1 additional electron, making 10.- \(\text{Na}^{+}\): Sodium normally has 11 electrons. With a \(+1\) charge, it has lost 1 electron, resulting in 10.- \(\text{Mg}^{2+}\): Magnesium normally has 12 electrons. With a \(+2\) charge, it has lost 2 electrons, making 10.

Step 3: Confirm Each Species in Option (a) Has 10 Electrons

Each species (\(\text{O}^{2-}, \text{F}^{-}, \text{Na}^{+}, \text{Mg}^{2+}\)) has 10 electrons, confirming they are isoelectronic, as they all have the same number of electrons.

Step 4: Analyze Other Options (b), (c), and (d)

- Option (b): \(\text{O}^{-}\) (9 electrons), \(\text{F}^{-}\) (10 electrons), \(\text{Na}\) (11 electrons), \(\text{Mg}^{+}\) (11 electrons) are not isoelectronic.- Option (c): \(\text{O}^{2-}\) (10), \(\text{F}^{-}\) (10), \(\text{Na}\) (11), \(\text{Mg}^{2+}\) (10) mismatch with \(\text{Na}\).- Option (d): \(\text{O}^{-}\) (9), \(\text{F}^{-}\) (10), \(\text{Na}^{+}\) (10), \(\text{Mg}^{2+}\) (10) do not match, different electrons count for \(\text{O}^{-}\).

Key Concepts

Electronic Structure

The electronic structure of an atom refers to the arrangement of electrons around the nucleus. Electrons are distributed in energy levels or shells, and these configurations determine the chemical behavior of the atom.
Each atom has its unique atomic number, corresponding to the number of protons in its nucleus, and in a neutral atom, also the number of electrons. Understanding electronic structure is fundamental in predicting how atoms will interact. When atoms gain or lose electrons, they become ions, altering their electronic structure. Isoelectric species arise when different atoms or ions share identical electronic configurations.
This often results in similar chemical properties because chemical reactions are largely determined by electronic configuration.Atoms achieve stability by attaining a noble gas electronic configuration, leading many ions to become isoelectronic with noble gases. For instance, the ions \(\text{O}^{2-}, \text{F}^{-}, \text{Na}^{+}, \text{Mg}^{2+}\) all have 10 electrons, sharing the electronic structure of neon.

Chemical Properties

Chemical properties of substances are determined largely by their electronic structures. For isoelectronic species, their identical number of electrons often leads to similar chemical properties.
This is because these properties derive from an atom's ability to form bonds, lose or gain electrons, and engage in reactions.While their electron configurations might be identical, isoelectronic species can exhibit differences in other chemical behavior due to variations in atomic size and charge. Ions such as \(\text{O}^{2-}, \text{F}^{-}, \text{Na}^{+}, \text{Mg}^{2+}\) are all isoelectronic, sharing similar reactions with certain reagents.
However, their solubility in water, interaction with other ions, and position on the periodic table can influence their exact chemical responses.It's crucial to remember that even with the same electronic structure, other factors such as atomic nucleus size, mass, and overall charge can affect the chemical behavior of these ions.

Ions and Electrons

Understanding ions and electrons is key to grasping the concept of isoelectronic species. An ion is a charged entity formed when an atom gains or loses electrons.
Typically, atoms lose or gain electrons to achieve a full outer electron shell, a configuration that's energetically favorable. When an atom becomes an ion, its number of electrons differs from its number of protons, resulting in a positive or negative charge.For example:

• Oxygen Ion \(\text{O}^{2-}\): Gained two electrons, becoming a negatively charged ion.
• Fluoride Ion \(\text{F}^{-}\): Gained one electron, resulting in a negative charge.
• Sodium Ion \(\text{Na}^{+}\): Lost one electron, resulting in a positive charge.
• Magnesium Ion \(\text{Mg}^{2+}\): Lost two electrons, leading to a double positive charge.

These ions are isoelectronic because they all have ten electrons. This leads to a stable electronic configuration similar to the noble gas, neon. Such configurations guide chemical interactions and the formation of compounds.