Problem 63 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Among the following ions which one has the highest paramagnetism? (a) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\) (b) \(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (c) \(\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (d) \(\left[\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\)

Step-by-Step Solution

Answer

The ion with the highest paramagnetism is \([\text{Fe}(\text{H}_2\text{O})_6]^{2+}\).

Step 1: Understand Paramagnetism

Paramagnetism refers to the phenomenon where a material is attracted by an external magnetic field due to the presence of unpaired electrons. The ion with the maximum number of unpaired electrons will exhibit the highest paramagnetism.

Step 2: Determine Electronic Configurations

Evaluate the electronic configurations of the central metal ions:\(\text{Cr}^{3+}: [Ar] 3d^3\), \(\text{Fe}^{2+}: [Ar] 3d^6\), \(\text{Cu}^{2+}: [Ar] 3d^9\), \(\text{Zn}^{2+}: [Ar] 3d^{10}\). Count the unpaired electrons for each to determine paramagnetism.

Step 3: Count Unpaired Electrons

- \(\text{Cr}^{3+}\): 3 unpaired electrons (3d^3)- \(\text{Fe}^{2+}\): 4 unpaired electrons (3d^6, configuration is t₂g³e_g²)- \(\text{Cu}^{2+}\): 1 unpaired electron (3d^9)- \(\text{Zn}^{2+}\): 0 unpaired electrons (3d^{10})

Step 4: Determine Highest Paramagnetism

Compare the number of unpaired electrons. \(\text{Fe}^{2+}\) with 4 unpaired electrons has the highest paramagnetism among the given ions.

Key Concepts

Unpaired Electrons

Unpaired electrons play a crucial role in determining the magnetic properties of an ion or a molecule. These electrons do not pair up with another electron having opposite spin within the same orbital. As a result, they contribute a net magnetic moment, which makes the substance paramagnetic. In simple terms, paramagnetic materials are attracted by magnets, thanks to these lone, unpaired electrons.
The presence of unpaired electrons is what makes an ion or molecule react to an external magnetic field. The more unpaired electrons there are, the stronger the reaction, meaning higher paramagnetism. Metals and ions that are associated with unpaired electrons tend to exhibit paramagnetic properties.
In the context of our example, it's the count of these unpaired electrons that tells us how much each ion will react to a magnetic field. For instance,

• Cr³⁺ has 3 unpaired electrons,
• Fe²⁺ has 4,
• Cu²⁺ has 1,
• while Zn²⁺ has none.

Thus, in this case, Fe²⁺ has the highest paramagnetism due to having the highest number of unpaired electrons.

Electronic Configurations

Electronic configuration is a way to represent the arrangement of electrons in an atom or ion. Each electron occupies an orbital, which is nothing but a region within the atom where the probability of finding an electron is highest. The placement of electrons determines the chemical properties and reactivity of an element or compound.
For transition metal ions, the filling of \[d\text{-orbitals}\] is particularly important because it greatly influences their color, magnetism, and catalytic activities. Electronic configurations are often written in a shorthand notation, which uses the closest noble gas configuration to simplify the expression of \[\text{d-electrons}\].
Let's look at a few examples to illustrate this concept:

• For \(\text{Cr}^{3+}\), the configuration is \([\text{Ar}] 3d^3\),
• \(\text{Fe}^{2+}\) is \([\text{Ar}] 3d^6\),
• \(\text{Cu}^{2+}\) comes in as \([\text{Ar}] 3d^9\),
• and \(\text{Zn}^{2+}\) \([\text{Ar}] 3d^{10}\).

This configuration is crucial as it intimately relates to the number of unpaired electrons, thereby determining the degree of paramagnetism each ion can exhibit.

Transition Metal Ions

Transition metal ions are a fascinating class of elements primarily found in the d-block of the periodic table. They are special because of the unique way their \[d\text{-orbitals}\] are filled or partially filled. Transition metals include elements like iron, copper, zinc, and chromium, usually known for their vibrant colors and magnetic properties.
One defining feature of these ions is their varying oxidation states, allowing them to form several distinct ionic species. This variability not only affects their chemical reactivity and coordination properties but also their electronic and magnetic characteristics.
The ions we examined, such as \(\text{Fe}^{2+}, \text{Cu}^{2+}, \text{Cr}^{3+}\), and \(\text{Zn}^{2+}\), showcase the diversity among transition metals:

• Each metal can lose different numbers of electrons to form different ions.
• The extent of unpaired electrons in \[d\text{-orbitals}\] influences their paramagnetic behavior.
• Due to their transition nature, they often display characteristic properties like being excellent conductors of electricity and having high melting points.

Thus, understanding the nature of transition metal ions provides valuable insights into the way they interact with magnetic fields, behave in chemical reactions, and find applications in diverse fields such as catalysis and material science.