Problem 203 - A Complete Resource Book in Chemistry for JEE Main

Question

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

Step-by-Step Solution

Answer

Set (c) does not contain isoelectronic species.

Step 1: Understanding Isoelectronic Species

Isoelectronic species have the same number of electrons and, generally, the same arrangement of electrons. This property often results in similar chemical properties. To identify isoelectronic species, we need to count the total number of electrons in each ion or molecule.

Step 2: Count Total Electrons in Set (a)

For \( \mathrm{CN}^{-} \): \( \mathrm{C} \) has 6 electrons and \( \mathrm{N} \) has 7 electrons, plus one extra for the negative charge, totaling 14 electrons. For \( \mathrm{N}_{2} \): Each \( \mathrm{N} \) has 7 electrons, totaling 14 electrons. For \( \mathrm{C}_{2}^{2-} \): Each \( \mathrm{C} \) has 6 electrons, plus two extra for the charge, totaling 14 electrons. Thus, all species have 14 electrons.

Step 3: Count Total Electrons in Set (b)

For \( \mathrm{PO}_{4}^{3-} \): \( \mathrm{P} \) has 15 electrons and each \( \mathrm{O} \) has 8 electrons. Total = \( 15 + 32 + 3 = 50 \) electrons. For \( \mathrm{SO}_{4}^{2-} \): \( \mathrm{S} \) has 16 electrons, totaling \( 16 + 32 + 2 = 50 \) electrons. For \( \mathrm{ClO}_{4}^{-} \): \( \mathrm{Cl} \) has 17 electrons, totaling \( 17 + 32 + 1 = 50 \) electrons.

Step 4: Count Total Electrons in Set (c)

For \( \mathrm{SO}_{3}^{2-} \): \( \mathrm{S} \) has 16 electrons, totaling \( 16 + 24 + 2 = 42 \) electrons. For \( \mathrm{CO}_{3}^{2-} \): \( \mathrm{C} \) has 6 electrons, totaling \( 6 + 24 + 2 = 32 \) electrons. For \( \mathrm{NO}_{3}^{-} \): \( \mathrm{N} \) has 7 electrons, totaling \( 7 + 24 + 1 = 32 \) electrons. \( \mathrm{SO}_{3}^{2-} \) is not isoelectronic with the others.

Step 5: Count Total Electrons in Set (d)

For \( \mathrm{BO}_{3}^{3-} \): \( \mathrm{B} \) has 5 electrons, totaling \( 5 + 24 + 3 = 32 \) electrons. For \( \mathrm{CO}_{3}^{2-} \): From Step 4, this has 32 electrons. For \( \mathrm{NO}_{3}^{-} \): From Step 4, this also has 32 electrons.

Key Concepts

Electron Count

Counting electrons helps us determine the arrangements and properties of molecules. To find the total electron count of a species, we add up the electrons contributed by each atom. Remember to adjust for any charges. For negatively charged ions, add an electron for every negative charge. For positively charged ions, subtract an electron for each positive charge.

When you know the electron count, check if different combinations of atoms or ions give the same count. This can help you compare molecules to see if they are isoelectronic.

Molecular Ions

Molecular ions are molecules that carry a charge due to the loss or gain of one or more electrons. These charges can alter the properties of the molecule.

Here’s how you determine their electron count:

• Start with the neutral atom’s electron count.
• Add or remove electrons based on the charge shown by the ion.

Identifying molecular ions is essential for understanding reactions and behavior because they often form key intermediates in chemical processes.

Electron Configuration

The electron configuration of atoms and ions describes how electrons are distributed in atomic orbitals. This is crucial for understanding chemical bonding and molecular structure.

Electrons fill orbitals in a specific order, generally starting from the lowest energy level. Knowing this order (often represented in terms of s, p, d, and f orbitals) can clarify how electrons are structured within molecules.

Isoelectronic species share an important aspect of electron configuration, which means they usually have similar such configurations. This often leads to similar chemical behaviors and bonding patterns.

Chemical Properties

Isoelectronic species tend to have similar chemical properties because their electron configurations are similar. This similarity means they often participate in similar reactions or form similar bonds.

However, differences in other aspects such as nuclear charge or atomic size can influence the exact nature and strength of these reactions.

Understanding chemical properties in the context of isoelectronic species can aid in predicting how different materials behave in various chemical environments. Such insights can be incredibly useful in fields like material science or biology.