Class 12 Chemistry - KARNATAKA
The d- and f-Block Elements
The chapter 'The d- and f-Block Elements' in Class 12 Chemistry explores the chemistry of transition and inner-transition elements. Students will learn about the electronic configurations, general properties like variable oxidation states, coloured ions, catalytic behavior, and complex formation of d-block elements (transition metals). It also covers the lanthanoids and actinoids of the f-block, focusing on phenomena like lanthanoid contraction. This chapter is highly scoring in Karnataka (KSEEB) board exams, frequently testing reasoning questions based on trends in atomic radii, magnetic moments, and stability of oxidation states.
Start Learning FreeKey Concepts
Transition Elements (d-Block)
Elements in groups 3-12 that have incompletely filled d-orbitals in their ground state or in any of their common oxidation states.
Lanthanoid Contraction
The steady decrease in atomic and ionic radii of lanthanoids with increasing atomic number, caused by the poor shielding effect of 4f electrons.
Magnetic Moment
A property of transition metal ions with unpaired electrons, calculated using the spin-only formula.
Interstitial Compounds
Compounds formed when small atoms like H, C, or N are trapped inside the crystal lattices of transition metals.
Potassium Permanganate Preparation
Prepared commercially by the fusion of pyrolusite (MnO2) with KOH in the presence of air or an oxidizing agent like KNO3.
Important Formulas
Board Exam Info
In the Karnataka (KSEEB) Class 12 Chemistry board exam, this chapter typically carries around 5 to 7 marks. Questions usually include 1-mark objective questions, 2-mark reasoning questions (such as explaining why transition metals act as good catalysts or why Zn, Cd, and Hg are not considered true transition elements), and occasional 3-mark descriptive questions on the preparation and properties of KMnO4 or K2Cr2O7.
Frequently Asked Questions
Why are Zn, Cd, and Hg not regarded as transition elements?
Because they have completely filled d-orbitals (d10) in their ground state as well as in their common oxidation states, lacking the typical properties of transition metals.
What is lanthanoid contraction and what are its consequences?
It is the gradual decrease in ionic radii across the lanthanoid series due to poor shielding by 4f electrons. Its main consequences include the nearly identical radii of 4d and 5d transition series elements (e.g., Zr and Hf).
Why do transition metals form coloured ions?
Due to the presence of unpaired d-electrons which undergo d-d transitions by absorbing light from the visible region of the spectrum.
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