Problem 35 - A Complete Resource Book in Chemistry for JEE Main

Question

General electronic configuration of lanthanides is (a) \((\mathrm{n}-2) \mathrm{f}^{1-14}(\mathrm{n}-1) \mathrm{s}^{2} \mathrm{p}^{6} \mathrm{~d}^{0-1} \mathrm{~ns}^{2}\) (b) \((\mathrm{n}-2) \mathrm{f}^{0-14}(\mathrm{n}-1) \mathrm{d}^{0-1} \mathrm{~ns}^{2}\) (c) \((\mathrm{n}-2) \mathrm{f}^{0-14}(\mathrm{n}-1) \mathrm{d}^{10} \mathrm{~ns}^{2}\) (d) \((\mathrm{n}-2) \mathrm{f}^{0-1}(\mathrm{n}-1) \mathrm{f}^{1-14} \mathrm{~ns}^{2}\)

Step-by-Step Solution

Answer

Option (b) is the correct general electronic configuration: \((n-2)f^{0-14}(n-1)d^{0-1}ns^2\).

Step 1: Identify Lanthanides

Lanthanides are a group of 15 elements in the periodic table from Lanthanum (La) to Lutetium (Lu), characterized by the filling of the 4f orbitals.

Step 2: Understand General Configuration

The general electronic configuration of lanthanides includes the progressive filling of 4f orbitals, with occasional filling of 5d orbitals due to closeness in energy.

Step 3: Analyze Configuration Options

- Option (a) suggests \[(n-2)f^{1-14}(n-1)s^2p^6d^{0-1}ns^2\] indicating the involvement of 4f, 5d and 6s subshells.- Option (b) suggests \[(n-2)f^{0-14}(n-1)d^{0-1}ns^2\] indicating a similar structure.- Option (c) suggests \[(n-2)f^{0-14}(n-1)d^{10}ns^2\] which is incorrect due to the mention of a full d10, not relevant in lanthanide series.- Option (d) suggests \[(n-2)f^{0-1}(n-1)f^{1-14}ns^2\] erroneously accounting for two f sublevel fillings, never occurs in lanthanides.

Step 4: Determine the Correct Configuration

Given that lanthanides fill the 4f orbital progressively and may affect the 5d orbital slightly (0-1 electron), the correct electronic configuration matches option (b): \[(n-2)f^{0-14}(n-1)d^{0-1}ns^2\] which effectively represents the 4f and occasional 5d electron occupancy.

Key Concepts

Periodic Table

The Periodic Table is an organized display of all known chemical elements. Each element is placed according to its atomic number, electron configurations, and recurring chemical properties. The lanthanides, also known as the lanthanoids, are a series of elements ranging from Lanthanum (La, atomic number 57) to Lutetium (Lu, atomic number 71). They are often broken out of the main body of the periodic table and placed below in a separate row to save space and make the chart more manageable.
Lanthanides fall into the f-block of the periodic table. This category is characterized by the progressive filling of 4f orbitals as their atomic numbers increase. These elements are typically shiny and silvery-white, known for their high magnetic susceptibility and luminescence. They are found naturally in various minerals and are used in numerous applications like electronics, superconductors, and powerful magnets.

4f orbitals

The 4f orbitals are a set of seven orbitals found in the lanthanides and are part of the f-block in the periodic table. These orbitals have a complex shape, which makes them distinct from the s, p, and d orbitals. They have a higher energy level than 3d or 4d orbitals despite being part of the fourth principal energy level.
In the context of lanthanides, electrons begin to fill these orbitals starting from Cerium (Ce, atomic number 58) and continue filling up to Lutetium (Lu, atomic number 71). The filling of 4f orbitals is crucial as it influences the unique properties of each element in this series. These properties include magnetic behavior and spectral characteristics, which are vital for their use in various technologies.

Electron configuration patterns

Understanding electron configuration patterns help to predict how electrons are distributed in an atom's orbitals. In the case of lanthanides, the general pattern features the filling of the 4f orbitals, with the electron configuration written as often \\((n-2)f^{1-14}(n-1)d^{0-1}ns^2\). This configuration shows the gradual filling of the 4f subshell from 1 up to 14 electrons, sometimes with 0 or 1 electron in the 5d subshell, and 2 electrons in ns subshell.
The lanthanides' electron configurations are important to understand because they determine the chemical behavior and bonding characteristics of each element. These filled electron orbitals influence how each element behaves chemically and physically, explaining why lanthanides are so similar yet subtly different.

5d orbitals

The 5d orbitals play a supportive role in the configuration of lanthanide elements. Though primarily known for the filling of 4f orbitals, the 5d orbitals can sometimes influence the overall electron configuration of these elements.
While 4f orbitals dominate, sporadically, the 5d orbitals might contain 0 to 1 electron. This occasional occupancy is due to the close energy levels between 4f and 5d orbitals, allowing electrons to "spill over." The configuration might appear as \\((n-1)d^{0-1}\), or sometimes fully unoccupied.
Due to their complex shapes, 5d orbitals are often less involved in bonding but are crucial for defining the electronic structure of transition metals and lanthanides' transition behaviors. Understanding their role in the periodic table helps us predict the properties of these elements more accurately.