Problem 103 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is/are characteristics of d-block elements? (a) They are generally diamagnetic (b) They form coloured complexes (c) They show variable oxidation states (d) Their ionization energies are very high

Step-by-Step Solution

Answer

Characteristics (b) and (c) are correct for d-block elements.

Step 1: Understanding the Question

The question is asking us to identify the characteristics that are true for elements in the d-block of the periodic table. The d-block elements are also known as transition metals.

Step 2: Examine Characteristic (a)

Statement (a) claims that d-block elements are generally diamagnetic. Diamagnetism occurs when all electrons are paired. However, d-block elements often have unpaired electrons due to partially filled d-orbitals, making them usually paramagnetic. Therefore, (a) is not correct.

Step 3: Examine Characteristic (b)

Statement (b) claims that d-block elements form coloured complexes. This is true because the d-d transitions of electrons in d-orbitals often result in the formation of coloured complexes.

Step 4: Examine Characteristic (c)

Statement (c) claims that d-block elements show variable oxidation states. This is correct as d-block elements can form ions by losing different numbers of d-electrons, leading to multiple oxidation states.

Step 5: Examine Characteristic (d)

Statement (d) claims that d-block elements have very high ionization energies. While they have relatively high ionization energies compared to s and p-block elements, they are not exceedingly high, making this statement incorrect.

Step 6: Conclusion

Based on the examination of each statement, (b) and (c) are correct characteristics of the d-block elements.

Key Concepts

Characteristics of Transition Metals

Transition metals, found in the d-block of the periodic table, possess unique characteristics that set them apart from other elements. These elements, such as iron, copper, and nickel, have partially filled d-orbitals. This gives them a distinct set of properties:

• **Multiple Oxidation States**: Transition metals often display a variety of oxidation states. This means they can lose different numbers of electrons, typically from their d and s orbitals. For example, iron can exist in +2 and +3 states.
• **Formation of Colored Compounds**: When transition metals form compounds, they often result in vivid colors. This happens because of electronic transitions between d-orbitals, popularly known as d-d transitions.
• **Catalytic Properties**: Many transition metals and their compounds act as catalysts. They can accelerate chemical reactions without being consumed in the process.
• **Paramagnetism**: Due to unpaired electrons in their d-orbitals, many d-block elements are paramagnetic. This contrasts with diamagnetic materials, which have all paired electrons.

These characteristics make transition metals incredibly useful in industrial applications, from catalysts to pigments.

Magnetic Properties of d-block Elements

The magnetic properties of d-block elements are influenced by the presence of unpaired electrons in their d-orbitals. This typically results in paramagnetism, where materials are attracted to magnetic fields.
The more unpaired electrons present, the stronger the paramagnetic effect.

• **Paramagnetism Explained**: In paramagnetic substances, the unpaired electrons' magnetic moments do not cancel out, thus they align with external magnetic fields.
• **Comparison to Diamagnetism**: Unlike paramagnetic materials, diamagnetic materials have all their electrons paired, leading to a repulsion from magnetic fields. Thus, most d-block elements, with their partially filled orbitals, fall under the paramagnetic category.
• **Effect in Practice**: The magnetic property can influence the behavior of materials made with these elements, important in manufacturing electronics and other magnetic materials.

Understanding these properties is crucial, not just theoretically, but also for practical applications that rely on these magnetic effects.

d-block Element Oxidation States

D-block elements are well-known for their ability to exhibit multiple oxidation states. This versatility arises due to their electron configuration within the d and s orbitals.
The available d and s electrons can be removed, which leads to a variety of stable ionic forms.

• **Multiple States Availability**: Transition metals can lose electrons from both their outer s and d orbitals, which gives rise to different oxidation states. For instance, manganese exhibits a wide range of oxidation states from +2 to +7.
• **Chemical Reactivity**: This variability influences the chemical reactivity and bonding behavior of transition metals. It allows them to participate in various chemical reactions and bond with different elements.
• **Relevance in Chemistry**: The ability to stabilize various oxidation states makes these metals valuable in catalytic processes and in forming compounds with diverse chemical properties.

In summary, the oxidation state variations play a pivotal role in the chemical versatility and applications of d-block elements across different fields.