Class 12 Chemistry - KERALA
The d- and f-Block Elements
The d- and f-Block Elements chapter for Class 12 Kerala SCERT chemistry explores the transition metals in groups 3-12 and the inner transition elements (lanthanoids and actinoids). Students study their electronic configurations, general characteristics such as variable oxidation states, coloured ions, catalytic properties, and alloy formation. The chapter also covers important compounds like potassium dichromate and potassium permanganate, alongside the unique phenomenon of lanthanoid contraction. Mastering this chapter is crucial for Kerala board exams as it consistently yields high-scoring conceptual questions, reasoning-based problems, and preparation methods for crucial chemical reagents.
Start Learning FreeKey Concepts
Transition Elements
Elements that have incompletely filled d-orbitals in their ground state or in any of their oxidation states, generally classified under groups 3 to 12.
Lanthanoid Contraction
The steady decrease in atomic and ionic radii of lanthanoid elements with increasing atomic number, caused by the poor shielding effect of 4f electrons.
Variable Oxidation States
Transition metals exhibit multiple oxidation states because the energy difference between (n-1)d and ns orbitals is very small, allowing both to participate in bonding.
Catalytic Properties
d-Block elements act as effective catalysts due to their ability to adopt multiple oxidation states and provide a large surface area with free valencies.
Preparation of Potassium Permanganate
Prepared commercially by the fusion of pyrolusite ore (MnO2) with alkali metal hydroxide in the presence of an oxidizing agent like KNO3, followed by electrolytic oxidation.
Important Formulas
Board Exam Info
In the Kerala (SCERT) Class 12 Chemistry board examination, this chapter typically carries around 6 to 8 marks. Questions frequently include reasoning-based items about colour and magnetic properties, comparative questions on lanthanoid and actinoid contraction, and balanced chemical equations for the preparation and reactions of KMnO4 and K2Cr2O7.
Frequently Asked Questions
Why do transition metals form coloured ions?
Transition metal ions form coloured compounds due to d-d electron transitions, where electrons absorb visible light to jump from lower to higher energy d-orbitals.
What are the consequences of lanthanoid contraction?
It results in the close similarity in size of elements in the second and third transition series (e.g., Zr and Hf), making them difficult to separate.
Why is zinc not considered a true transition element?
Zinc has a completely filled d-subshell (3d10) in its ground state as well as in its common oxidation state (Zn2+), failing the definition of a transition element.
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