Introduction:

The d-block elements, also known as transition elements, are a vital part of Class 12 Chemistry. These elements exhibit unique properties due to their partially filled d-orbitals, making them essential for understanding chemical bonding, coordination chemistry, and periodic trends. This guide provides a detailed overview of the electronic configurations of d-block elements, enabling students to grasp the concepts clearly and excel in their examinations.



What are d-Block Elements?

The d-block elements are positioned in groups 3 to 12 of the periodic table. They are called transition elements because they bridge the s- and p-block elements. The distinguishing feature of these elements is the filling of the d-orbitals in their electron configurations.

General Electronic Configuration of d-Block Elements:

The general electronic configuration of d-block elements is:

(n-1)d^{1-10}ns^{0-2}

Here, (n) represents the principal quantum number. These elements usually have one or two electrons in the outermost s-orbital, with the remaining electrons populating the (n-1)d orbitals.

Exceptions in Electronic Configurations:

Some d-block elements deviate from the expected configurations due to the stability associated with half-filled and fully filled orbitals. For instance:

- Chromium (Cr): [Ar] 3d⁵ 4s¹ (Instead of 3d⁴ 4s²)

- Copper (Cu): [Ar] 3d¹⁰ 4s¹ (Instead of 3d⁹ 4s²)

Trends in d-Block Elements:

Atomic and Ionic Radii:

 - Decrease across a period due to increased nuclear charge.

 - Slight increase down a group due to the addition of a new energy level.

Ionization Enthalpy:

 - Generally increases across a period.

 - Exceptions occur due to electron pairing in d-orbitals.

Oxidation States:

 - d-block elements exhibit variable oxidation states because electrons from both (n-1)d and ns orbitals can participate in bonding.

Read Also: Abnormal Molar Masses - Detailed Class 12 Chemistry Notes

Importance of d-Block Elements:

- Catalysis: Many d-block elements, like iron and nickel, are used as catalysts.

- Magnetism: Due to unpaired electrons, these elements show paramagnetic and ferromagnetic behavior.

- Alloy Formation: Their ability to form alloys makes them invaluable in metallurgy.

Applications in Real Life:

1. Iron is essential for steel production.

2. Titanium is used in aerospace engineering due to its strength and corrosion resistance.

3. Copper and silver are widely used in electrical and thermal conductors.

4. Platinum is significant in catalysis and jewellery.

Conclusion:

The electronic configurations of d-block elements form the foundation of their chemical behavior and diverse applications. Understanding these configurations not only aids in mastering periodic trends but also lays the groundwork for advanced topics like coordination chemistry and material science. Mastery of this chapter ensures a strong grasp of fundamental concepts crucial for success in Class 12 Chemistry and beyond.