Class 12 Chemistry - TAMILNADU
The d- and f-Block Elements
The chapter 'The d- and f-Block Elements' in Tamil Nadu Class 12 Chemistry explores the transition metals in groups 3-12 and the inner transition elements (lanthanoids and actinoids). You will learn about their electronic configurations, characteristic properties like variable oxidation states, coloured ion formation, catalytic activity, and complex compound formation. Special emphasis is placed on the lanthanoid contraction and its consequences. This chapter is vital for board exams as it consistently contributes high-scoring conceptual questions, IUPAC naming of coordination entities, and reasoning questions that test your understanding of periodic trends.
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 increasing atomic number, caused by the imperfect shielding of nuclear charge by 4f electrons.
Variable Oxidation States
d-Block elements exhibit multiple oxidation states because the energy difference between (n-1)d and ns orbitals is very small, allowing electrons from both to participate in bonding.
Magnetic Moment
Transition metal ions exhibit paramagnetism due to the presence of unpaired electrons, calculated using the spin-only formula.
Inner Transition Elements (f-Block)
Elements in which the last electron enters the f-orbitals, divided into lanthanoids (4f series) and actinoids (5f series).
Important Formulas
Board Exam Info
In the Tamil Nadu (Samacheer Kalvi) Class 12 Chemistry board exam, this chapter typically carries around 6 to 8 marks. Questions frequently include one-mark objective queries, reasoning-based questions about colour and catalytic properties, short answers on lanthanoid contraction, and problems calculating the magnetic moment.
Frequently Asked Questions
Why do transition elements act as good catalysts?
Transition metals act as good catalysts due to their ability to exhibit variable oxidation states and provide a large surface area with vacant orbitals for reactants to adsorb.
What is lanthanoid contraction and what are its consequences?
It is the progressive decrease in atomic size of lanthanoids. Its major consequence is that the radii of the second and third row transition elements (like Zr and Hf) are very similar, making them difficult to separate.
Why are Zn, Cd, and Hg not considered true transition elements?
Because they have completely filled d-orbitals (d^10) in their ground state as well as in their common oxidation states, lacking the typical characteristics of transition metals.
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