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) \(\mathrm{La}\)

Step-by-Step Solution

Answer

(a) Eu

Step 1: Identify the Lanthanide Series

The lanthanide series comprises the 15 elements from atomic number 57 (lanthanum) to 71 (lutetium) on the periodic table. None of the elements except lanthanum, cerium, and europium are mentioned in the given options, and sodium (Na) is not a lanthanide.

Step 2: Understand Oxidation States of Lanthanides

In the lanthanide series, the most common oxidation state is "+3". However, certain elements also exhibit a "+2" oxidation state. These include europium (Eu), samarium (Sm), and ytterbium (Yb).

Step 3: Analyze the Given Options

Among the options, only europium (Eu) is known to commonly exist in both the "+2" and "+3" oxidation states. Cerium predominantly exhibits the "+3" and "+4" oxidation states, while lanthanum typically exists in the "+3" state.

Step 4: Review and Conclude

Given the analysis, the answer is europium (Eu), as it commonly forms both "+2" and "+3" oxidation states. While cerium and lanthanum can exhibit other oxidation states, "+2" is specifically common only to europium in the given options.

Key Concepts

Lanthanide Series

The lanthanide series includes 15 elements ranging from lanthanum (atomic number 57) to lutetium (atomic number 71). These elements are part of the rare earth metals and are known for their similar properties. Their general characteristics include:

• Silvery-white metals
• High melting and boiling points
• Good conductivity of electricity and heat

These elements play a crucial role in various technologies, such as electronic devices, magnets, and phosphors for lighting. While they behave similarly chemically, each element has unique properties that lend it specific applications. Understanding the lanthanide series is essential when exploring the properties of certain compounds and their uses in industries.

Oxidation States

Oxidation states are crucial in understanding how elements form compounds. In the context of lanthanides, the most prevalent oxidation state is "+3". However, some lanthanides exhibit other oxidation states due to their electronic configurations.

For instance:

• Europium, samarium, and ytterbium can also show a "+2" oxidation state because they can lose electrons to achieve a stable electronic configuration.
• Cerium can exhibit a "+4" oxidation state, which is unique among lanthanides and is particularly important in industrial applications like catalytic converters.

Understanding these oxidation states helps determine the reactivity and compatibility of these elements in forming various compounds.

Europium

Europium is a noteworthy lanthanide due to its ability to commonly exhibit two different oxidation states: "+2" and "+3". This property makes europium unique and valuable in several applications.

Europium's "+2" state allows it to be used in the manufacturing of phosphors that create high-quality red colors in televisions and LED lights. These phosphors are essential in improving the color and efficiency of display technologies.

• Highly reactive with air and water
• Utilized in anti-counterfeiting measures in banknotes
• Plays a role in nuclear reactors as a neutron absorber

The ability of europium to exist in multiple oxidation states gives it versatility, making it crucial in both research and production contexts.