NEET Notes: The d- and f-Block Elements

Introduction

The d- and f-block elements, also known as transition and inner transition elements, play a significant role in the periodic table. These elements exhibit unique chemical and physical properties due to their electronic configurations, variable oxidation states, and catalytic behavior. The d-block elements are found in groups 3 to 12, while the f-block elements, also known as lanthanides and actinides, are placed separately at the bottom of the periodic table.

d-Block Elements (Transition Elements)

1. Position in the Periodic Table

• The d-block elements are located in groups 3 to 12.

• They lie between the s-block and p-block elements.

2. Electronic Configuration

• The general electronic configuration is (n-1)d¹⁻¹⁰ ns¹⁻².

• These elements have partially filled d-orbitals, which influence their chemical properties.

3. General Characteristics

• Exhibit variable oxidation states.

• Form colored compounds.

• Show catalytic properties due to the availability of vacant d-orbitals.

• Have high melting and boiling points.

• Form complex compounds with ligands.

4. Variable Oxidation States

• Transition metals exhibit multiple oxidation states due to the involvement of both (n-1)d and ns electrons in bonding.

• For example, iron (Fe) shows +2 and +3 oxidation states, while manganese (Mn) can have oxidation states from +2 to +7.

5. Color of Compounds

• The presence of unpaired d-electrons causes d-d transitions, which absorb visible light and impart colors to the compounds.

• For example, Cu²⁺ ions appear blue, and Cr³⁺ ions appear green.

6. Magnetic Properties

• Transition metals exhibit paramagnetism due to the presence of unpaired electrons.

• The magnetic behavior increases with the number of unpaired electrons.

7. Catalytic Properties

• Many transition metals and their compounds act as catalysts due to their ability to change oxidation states.

• Examples include Fe in the Haber process and V₂O₅ in the Contact process.

8. Formation of Complexes

• Transition metals readily form coordination complexes with ligands.

• Examples: [Fe(CN)₆]³⁻, [Cu(NH₃)₄]²⁺.

9. Alloy Formation

• Transition metals form alloys with each other due to their similar atomic sizes.

• Examples: Stainless steel (Fe, Cr, Ni) and brass (Cu, Zn).

f-Block Elements (Inner Transition Elements)

1. Position in the Periodic Table

• The f-block elements include the lanthanides (atomic numbers 57-71) and actinides (atomic numbers 89-103).

• They are placed separately at the bottom of the periodic table.

2. Electronic Configuration

• The general electronic configuration is (n-2)f¹⁻¹⁴ (n-1)d⁰⁻¹ ns².

• The filling of 4f and 5f orbitals gives rise to the unique properties of these elements.

3. General Characteristics

• Exhibit variable oxidation states.

• Show high electropositivity and reactivity.

• Have a tendency to form colored ions.

• Exhibit paramagnetism due to unpaired f-electrons.

4. Lanthanides (Rare Earth Elements)

Properties of Lanthanides

• Show a common oxidation state of +3.

• Exhibit lanthanide contraction, leading to a gradual decrease in ionic radii.

• Have high melting and boiling points.

• Used in phosphors, magnets, and electronic devices.

Uses of Lanthanides

• Neodymium (Nd): Used in powerful magnets.

• Europium (Eu): Used in fluorescent lamps.

• Gadolinium (Gd): Used in MRI contrast agents.

5. Actinides (Radioactive Elements)

Properties of Actinides

• Show multiple oxidation states, commonly +3, +4, +5, and +6.

• Exhibit radioactivity, making them unstable.

• Have strong metallic properties.

• Form complexes with ligands such as phosphates and oxalates.

Uses of Actinides

• Uranium (U) and Plutonium (Pu): Used as nuclear fuels.

• Thorium (Th): Used in nuclear reactors.

Comparison Between d- and f-Block Elements

Applications of d- and f-Block Elements

1. Industrial Applications

• Used in the manufacture of steel and alloys.

• Catalysts in industrial processes like the Haber process (Fe) and hydrogenation reactions (Ni).

2. Medical Uses

• Titanium (Ti) and Zirconium (Zr) are used in surgical implants.

• Gadolinium (Gd) is used in MRI contrast agents.

3. Nuclear Energy

• Uranium (U) and Plutonium (Pu) are key fuels in nuclear reactors.

• Thorium (Th) is used in advanced nuclear technologies.

4. Electronic and Magnetic Uses

• Lanthanides are used in powerful magnets, LED screens, and batteries.

• Tungsten (W) is used in filaments of electric bulbs.

Conclusion

The d- and f-block elements are crucial in chemistry due to their diverse properties and applications. Transition metals show variable oxidation states, catalytic behavior, and alloy formation, whereas inner transition elements play a key role in nuclear technology and high-tech industries. Understanding their properties and uses is essential for NEET preparation.