Class 12 Chemistry - ANDHRA-PRADESH
The d- and f-Block Elements
The chapter 'The d- and f-Block Elements' in Class 12 Chemistry for Andhra Pradesh (BSEAP) students explores the chemistry of transition and inner-transition elements found in groups 3-12 and the bottom of the periodic table. You will learn about the electronic configurations, metallic character, variable oxidation states, coloured ions, catalytic properties, and complex compound formation of d-block elements (3d, 4d, 5d, and 6d series). Additionally, the chapter covers the lanthanoids and actinoids of the f-block, focusing on lanthanoid contraction and its consequences. This chapter is vital for board exams as it is rich in conceptual reasoning questions.
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.
Variable Oxidation States
d-Block elements exhibit multiple oxidation states due to the very small energy gap between $(n-1)d$ and $ns$ orbitals, allowing electrons from both to participate in bonding.
Coloured Ions
Most transition metal ions are coloured in solid state or in aqueous solution due to d-d electron transitions when visible light is absorbed.
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
Transition metal ions show paramagnetism due to unpaired d-electrons, calculated using the spin-only formula $\mu = \sqrt{n(n+2)}$.
Important Formulas
Board Exam Info
In the Andhra Pradesh (BSEAP) Class 12 Chemistry board examinations, this chapter typically carries around 4 to 6 marks. Questions usually include very short answer questions (1 mark), short answer questions (2 or 4 marks) focusing on reasons for properties like colour, catalytic behaviour, and variable oxidation states, and problems based on the spin-only magnetic moment.
Frequently Asked Questions
Why are transition metals and their compounds often catalytic in nature?
They show catalytic activity due to their ability to adopt multiple oxidation states and provide a suitable surface with free valencies for reactant molecules to adsorb.
What is lanthanoid contraction and what are its main consequences?
It is the gradual decrease in size of lanthanoid atoms/ions. Its main consequences include the similarity in size of 4d and 5d series elements (e.g., Zr and Hf) and difficulty in their separation.
Why is zinc (Zn) not considered a true transition element?
Zinc has a completely filled d-orbital ($3d^{10}4s^2$) in its ground state as well as in its common oxidation state ($Zn^{2+}$), which does not satisfy the definition of a transition element.
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