d-Block and f-Block Elements – Transition and Inner Transition Elements
1. General Introduction to d-Block and f-Block Elements
The d-block and f-block elements are transition and inner transition elements, respectively. The d-block elements are located in groups 3 to 12 of the periodic table, while the f-block elements, also known as inner transition elements, are found in the lanthanoid and actinoid series.
2. Electronic Configuration of Transition Elements
Transition elements have partially filled d-orbitals. The general electronic configuration of transition elements is (n-1)d¹–¹⁰ ns¹–². These elements exhibit a wide variety of oxidation states due to the availability of d-electrons for bonding.
3. Properties of d-Block (Transition) Elements
Transition elements exhibit unique properties due to the presence of d-electrons:
- Physical Properties: These elements have high melting and boiling points, high density, and good electrical and thermal conductivity.
- Ionization Enthalpy: Transition metals have relatively high ionization enthalpy, though it does not increase significantly across the period.
- Oxidation States: Transition elements show a wide range of oxidation states, typically from +1 to +7, due to the involvement of both s and d electrons in bonding.
- Atomic Radii: The atomic radii of transition elements do not decrease significantly across a period due to the poor shielding of nuclear charge by d-electrons.
- Colour: Many transition metal compounds are colored due to d-d transitions when electrons absorb light and move between d-orbitals.
- Catalytic Behaviour: Transition metals act as catalysts in a variety of chemical reactions due to their ability to adopt multiple oxidation states and facilitate electron transfer.
- Magnetic Properties: Transition metals can exhibit magnetic properties due to unpaired electrons in their d-orbitals, which contribute to their paramagnetism.
- Complex Formation: Transition metals readily form coordination compounds due to their ability to accept electron pairs from ligands.
- Interstitial Compounds: Transition elements form interstitial compounds with small atoms like hydrogen, carbon, and nitrogen filling the interstitial spaces in the metal lattice.
- Alloy Formation: Transition metals are widely used to form alloys, such as steel, due to their malleability and resistance to corrosion.
4. Preparation, Properties, and Uses of K₂Cr₂O₇ and KMnO₄
Potassium dichromate (K₂Cr₂O₇) and potassium permanganate (KMnO₄) are important compounds of transition elements with a wide range of industrial applications:
- K₂Cr₂O₇: Prepared by reacting chromium ore with potassium carbonate and sodium carbonate. It is used in electroplating, as a disinfectant, and in organic synthesis.
- KMnO₄: Prepared by oxidizing manganese dioxide with potassium hydroxide. It is used as an oxidizing agent in titrations, water treatment, and as a disinfectant.
5. Inner Transition Elements
The inner transition elements are the lanthanoids and actinoids. They are placed in two rows below the main body of the periodic table to maintain its structure.
6. Lanthanoids
Lanthanoids are elements in the 4f block, ranging from lanthanum (La) to lutetium (Lu). They have similar chemical properties and exhibit a gradual contraction in atomic and ionic radii, known as the lanthanoid contraction.
- Electronic Configuration: Lanthanoids have the general electronic configuration of (n-2)f¹–¹⁴ ns².
- Oxidation States: The most common oxidation state of lanthanoids is +3, but they can also show oxidation states of +2 and +4 in some cases.
- Lanthanoid Contraction: Due to poor shielding of the nucleus by the f-electrons, the size of lanthanoids decreases as you move across the series.
7. Actinoids
Actinoids are elements in the 5f block, ranging from actinium (Ac) to lawrencium (Lr). Many actinoids are radioactive and exhibit a variety of oxidation states.
- Electronic Configuration: Actinoids have the general electronic configuration of (n-2)f¹–¹⁴ ns².
- Oxidation States: Actinoids exhibit a wide range of oxidation states, typically from +3 to +7, with the +3 oxidation state being the most common.