Science Class 12 - D F-Block-Elements Notes

d- and f-Block Elements

Welcome to the chapter on d- and f-Block Elements for Class 12. In this chapter, you will learn about the properties, electronic configurations, trends, and important compounds of the d- and f-block elements. By the end of this chapter, you will understand their position in the periodic table, their unique characteristics, and their uses in daily life and industry.

Introduction

The d-block elements are also called transition elements and are found in groups 3 to 12 of the periodic table. The f-block elements, known as inner transition elements, include the lanthanides and actinides, which are placed separately at the bottom of the periodic table.

Electronic Configuration

• d-block: General configuration is (n-1)d^1-10ns^0-2.
• f-block: General configuration is (n-2)f^1-14(n-1)d^0-1ns².

General Properties of d-Block Elements

• Show variable oxidation states.
• Form colored ions and compounds.
• Often act as good catalysts.
• Exhibit paramagnetism due to unpaired electrons.
• Form complex compounds.

General Properties of f-Block Elements

• Include lanthanides (atomic numbers 58–71) and actinides (atomic numbers 90–103).
• Show variable oxidation states, but +3 is most common.
• Lanthanides are known for lanthanide contraction.
• Actinides are mostly radioactive.
• Form colored ions and complex compounds.

Important Trends and Concepts

• Atomic and ionic sizes: Decrease across the period due to increased nuclear charge.
• Ionization enthalpy: Increases across the period.
• Magnetic properties: Due to unpaired d or f electrons.
• Lanthanide contraction: Steady decrease in ionic radii of lanthanides with increasing atomic number.

Important Compounds and Uses

• Transition metals are used in making alloys (steel, stainless steel, bronze).
• Compounds like potassium dichromate (K₂Cr₂O₇) and potassium permanganate (KMnO₄) are important oxidizing agents.
• Lanthanides are used in making strong magnets and color TV screens.
• Actinides like uranium and plutonium are used as nuclear fuels.

Practice Questions

1. Write the general electronic configuration of d-block elements.
2. What is lanthanide contraction? State its consequences.
3. Why do transition metals show variable oxidation states?
4. Name two important uses of actinides.
5. Which property makes transition metals good catalysts?

Challenge Yourself

• Explain why Zn, Cd, and Hg are not considered transition elements.
• Describe the color and magnetic properties of d-block ions with examples.

Did You Know?

• Gold and platinum are d-block elements and are highly valued for their beauty and rarity.
• All actinides are radioactive, and some are used in nuclear reactors and weapons.

Glossary

• Transition elements: Elements in the d-block showing variable oxidation states and forming colored ions.
• Lanthanides: 14 elements after lanthanum (atomic numbers 58–71).
• Actinides: 14 elements after actinium (atomic numbers 90–103).
• Lanthanide contraction: Gradual decrease in the size of lanthanide ions.
• Paramagnetism: Property of substances with unpaired electrons to be attracted by a magnetic field.

Answers to Practice Questions

1. (n-1)d^1-10ns^0-2
2. Lanthanide contraction is the steady decrease in the size of lanthanide ions as atomic number increases. It leads to similarities in the properties of 4d and 5d transition elements.
3. Due to the presence of closely lying energy levels of (n-1)d and ns orbitals, electrons can be lost from both, leading to variable oxidation states.
4. Used as nuclear fuels (uranium, plutonium) and in making atomic bombs.
5. Their ability to change oxidation states and form complexes makes them good catalysts.

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Understanding d- and f-block elements helps you explore the world of advanced chemistry and its applications!