Problem 17 - A Complete Resource Book in Chemistry for JEE Main

Question

For which lanthanide are \(+2\) and \(+3\) oxidation states are common? (a) Eu (b) \(\mathrm{Na}\) (c) \(\mathrm{Ce}\) (d) La

Step-by-Step Solution

Answer

(a) Eu

Step 1: Analyze the Options

The question asks us to identify the lanthanide element that commonly exhibits both +2 and +3 oxidation states. The options given are Eu (Europium), Na (Sodium), Ce (Cerium), and La (Lanthanum). First, note that Sodium (Na) is not a lanthanide, so it can be eliminated from consideration.

Step 2: Identify Common Oxidation States

Europium, Cerium, and Lanthanum are all lanthanides, but only certain lanthanides commonly exhibit multiple oxidation states. Typically, the +2 oxidation state is not common amongst all lanthanides, as they predominantly show +3. However, Europium (Eu) is known for its stable +2 state in addition to the +3 oxidation state.

Step 3: Verify with Lanthanide Properties

Europium is one of the few lanthanides that frequently forms compounds in the +2 state due to its stable half-filled f-shell configuration in Eu²⁺. Cerium can exhibit a +4 state besides +3, and Lanthanum predominantly shows +3. Therefore, Europium is the element that commonly exhibits both +2 and +3 oxidation states among these options.

Key Concepts

Oxidation States

In chemistry, the oxidation state of an element indicates the degree of oxidation of an atom. This concept is essential for understanding chemical reactions, especially those involving electron transfer. For lanthanides, oxidation states typically tell us how electrons are distributed in reactions.
A lanthanide usually exhibits a +3 oxidation state, which happens due to the loss of three electrons from their outermost shell. However, some elements in the lanthanide series can show other oxidation states. These variances occur due to specific electronic configurations.

• Most lanthanides exhibit the +3 oxidation state.
• Only a few, like Europium ( ext{Eu}), also show a +2 state.

The stability of different oxidation states is usually related to how electrons fill the available orbitals. For instance, the +2 state in Europium is quite stable, as we'll explore later. Understanding these states is crucial for predicting how these elements behave in chemical reactions.

Lanthanide Series

The lanthanide series includes 15 elements, sometimes known as rare earth elements, starting with Lanthanum ( ext{La}) and ending with Lutetium ( ext{Lu}). These elements are located at the bottom of the periodic table and are known for their unique properties.
This series is characterized by the gradual filling of the 4f electron shell. As we move from Lanthanum to Lutetium, each element has one more proton and one more 4f electron than the previous element.

• Typically, lanthanides are shiny and reactive metals.
• They have high melting points and are often used in alloys and catalysts.

Due to their magnetism and luminescence, lanthanides are in high demand for technology applications, such as smartphones and televisions. The unique electronic configurations of lanthanides are what make them so versatile, with some, like Europium, having more than one common oxidation state.

Europium Properties

Europium ( ext{Eu}) is a fascinating element within the lanthanide series, known for its distinctive ability to exhibit multiple oxidation states, specifically +2 and +3. This dual ability is thanks to its electronic configuration, which allows it to stabilize as Eu²⁺ and Eu³⁺.
In the +2 state, Europium has a half-filled 4f shell, offering remarkable stability. This half-filled state makes it unique among most lanthanides, which predominantly display only the +3 state.

• Europium is relatively soft and can easily oxidize in air.
• It is commonly found in phosphors for red and blue colors in television and LED screens.

Additionally, Europium is highly valued for its luminescent properties. Its compounds are integral to various applications in electronics and optoelectronics, making it an essential element in modern technologies.