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) \((n-2) f^{0-1}(n-1) f^{1-14} n s^{2}\)

Step-by-Step Solution

Answer

The general electronic configuration of lanthanides is (a).

Step 1: Identify Key Components of Electronic Configuration

Lanthanides are elements with atomic numbers from 57 to 71. Their key feature is filling of the f-orbital. Typically, their valence electronic configuration is influenced by both (n-2)f and (n-1)d orbitals alongside ns orbital.

Step 2: Analyze Lanthanide Block Characteristics

In lanthanides, the (n-2)f orbital has electrons ranging from 1 to 14, because lanthanides include the filling of these f-orbitals. The (n-1)d orbital can also be filled up to 1 electron, but in some instances, it remains unfilled. The ns orbital is consistently filled with 2 electrons.

Step 3: Evaluate Each Option for Correct Configuration

(a) contains \(n-2\)f^{1-14}, (b) contains \(n-2\)f^{0-14}, and (c) contains the same. All have \(n-1\)d^{0-1} since lanthanides typically just start filling d after f is complete. Option (d) starts with f^{0-1}, which does not fit the typical filling order.

Step 4: Select the Best Option

By filling in order based on lanthanide properties and typical filling patterns, option (a) \(n-2\)f^{1-14}(n-1)s^{2}p^{6}d^{0-1}ns^{2} captures the true characteristics of lanthanides as it provides ranges capturing typical electron occupations in f-block.

Key Concepts

f-block elements

The f-block elements are a unique set of elements found in the periodic table. They are known for their distinctive filling of electrons in the f-orbitals, which are deeper and more complex than the s, p, or d orbitals. These elements are characterized by their ability to hold a large number of electrons, typically ranging from 1 to 14, within the f-orbital. This large capacity allows the f-block to accommodate variations in electron configurations that aren't typically observed in other areas of the periodic table.

Primarily composed of the lanthanide and actinide series, the f-block elements are separated from the main body of the periodic table due to their unique electronic structure. This structure gives rise to their distinctive chemical and physical properties. For example, many of these elements exhibit increased levels of magnetism and luminescence, which makes them valuable in a range of applications from technology to research.

Understanding the f-block requires an appreciation for the energy levels and the complex electron interactions that occur within these orbitals. These interactions impact the chemical behavior of the elements significantly, influencing how they bond with other elements and their overall stability.

lanthanide series

The lanthanide series consists of 15 metallic elements with atomic numbers from 57 to 71, starting with lanthanum and ending with lutetium. This series is a subset of the f-block elements and is known for the filling of the 4f orbitals. As electrons are added across the series, the 4f orbitals fill successively.

Lanthanides are also referred to as 'rare earth elements,' though they are relatively abundant in the Earth's crust. These elements are particularly known for their similar chemical properties, which arise from the filling of the f-orbital. Despite this similarity, small differences in their electronic structures can lead to significant variations in their chemical and physical behaviors.

Common applications of lanthanides include their use in strong magnets, phosphors in color television and LED screens, and catalysts in various chemical reactions. The similar ionic radii and variable oxidation states often make separation of these elements from one another challenging, but their unique properties make them highly valued in various technological advancements.

electron filling order

The electron filling order is a rule used to predict the placement of electrons in an atom's orbitals. This order is crucial when determining the electronic configuration of elements, especially for transition series like the f-block. The filling follows the Aufbau principle, which states that electrons occupy the lowest energy orbital available.

For the f-block elements, this means electrons begin filling the f-orbital as soon as the s and p orbitals are filled to a certain capacity. Specifically, for the lanthanides, the 4f orbital electrons begin filling after the 6s orbital, according to the sequence:

• 6s
• 4f
• 5d (to a limited extent)

This peculiar filling order, which sometimes sees partial filling in the d-orbitals as well, is what accounts for the characteristic properties of the lanthanide series. Understanding this order is essential for predicting how these elements will engage in chemical bonding and reactions.

valence electrons

Valence electrons are the electrons present in the outermost shell of an atom and are vital in determining an element's chemical properties. For the lanthanides, identifying which electrons are considered valence can be complex due to the involvement of the f-orbitals and sometimes the d-orbitals.

Typically, the valence electrons for lanthanides include the ns electrons and those in the (n-1)d and (n-2)f orbitals. Though the main contributors in chemical reactions are the ns electrons, the involvement of f and d electrons can influence the complex electronic and magnetic behaviors observed in these elements.

Valence electrons play a fundamental role in bonding, affecting the reactivity and the types of bonds an element can form. In lanthanides, these electrons contribute to their relatively uniform oxidation state of +3, although variations do occur due to slightly different electron configurations in the series. This knowledge is crucial for the fields that employ lanthanides and rely on their unique chemical and physical traits.