Class 12 Chemistry - RAJASTHAN
The d- and f-Block Elements
The d- and f-Block Elements chapter in Class 12 Chemistry explores the chemistry of transition and inner-transition metals. Students learn about the general properties of d-block elements (Scandium to Zinc series) including variable oxidation states, coloured ions, catalytic properties, and alloy formation. The chapter also covers the preparation and properties of important compounds like potassium dichromate and potassium permanganate. Finally, it delves into f-block elements (lanthanoids and actinoids), emphasizing the causes and consequences of lanthanoid contraction. This chapter is highly scoring and frequently tested in Rajasthan Board (RBSE) examinations through conceptual and reasoning questions.
Start Learning FreeKey Concepts
Transition Elements (d-Block)
Elements that have incompletely filled d-orbitals in their ground state or in any of their oxidation states, generally occupying groups 3 to 12 in the periodic table.
Lanthanoid Contraction
The steady decrease in atomic and ionic radii of lanthanoids with an increase in atomic number, caused by the imperfect shielding of nuclear charge by 4f electrons.
Magnetic Moment
Calculated using the spin-only formula, it measures the magnetic behavior of transition metal ions based on the number of unpaired electrons present in d-orbitals.
Catalytic Properties
d-Block elements and their compounds act as good catalysts due to their ability to adopt multiple oxidation states and provide a large surface area with active sites.
Preparation of KMnO4
Potassium permanganate is prepared commercially by the fusion of pyrolusite ore (MnO2) with KOH in the presence of air or an oxidizing agent like KNO3, followed by electrolytic oxidation.
Important Formulas
Board Exam Info
In the Rajasthan (RBSE) Class 12 Chemistry board examination, this chapter typically carries around 4 to 6 marks. Questions frequently include reasoning-based problems regarding why transition metals form colored compounds or complex compounds, explanations of lanthanoid contraction and its consequences, and chemical equations for the preparation of potassium permanganate or potassium dichromate.
Frequently Asked Questions
Why are transition metal compounds generally coloured?
Transition metal compounds are coloured due to d-d electron transitions, where an electron absorbs visible light to jump from a lower energy d-orbital to a higher energy d-orbital.
What is lanthanoid contraction and what are its main consequences?
Lanthanoid contraction is the progressive decrease in atomic and ionic radii across the lanthanoid series. Its main consequences include the nearly identical radii of 4d and 5d transition series elements (e.g., Zr and Hf) and difficulty in separating lanthanoids.
Why do transition elements exhibit variable oxidation states?
Transition elements show variable oxidation states because the energy difference between (n-1)d and ns orbitals is very small, allowing electrons from both orbitals to participate in bonding.
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