Class 12 Chemistry - ODISHA
The d- and f-Block Elements
The chapter 'The d- and f-Block Elements' in Class 12 Chemistry covers the chemistry of transition and inner transition elements. Students will explore the general characteristics of d-block elements, such as variable oxidation states, coloured ion formation, catalytic activity, and alloy formation, with a special focus on potassium dichromate and potassium permanganate. Additionally, the chapter delves into f-block elements, dividing them into lanthanoids and actinoids, and discusses the prominent phenomenon of lanthanoid contraction. This chapter holds significant weight in the Odisha BSE board exams, frequently featuring direct conceptual questions, chemical preparation reactions, and reasoning-based problems that require a solid understanding of periodic trends.
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 oxidation states.
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.
Colour of Ions
Most transition metal ions are coloured due to d-d electron transitions, where an electron absorbs visible light and jumps from a lower to a higher d-orbital.
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.
Inner Transition Elements (f-Block)
Elements in which the last electron enters the f-orbitals, comprising the lanthanoid series (4f) and actinoid series (5f).
Important Formulas
Board Exam Info
In the Odisha BSE Class 12 Chemistry examination, this chapter typically carries around 4 to 6 marks. Common question types include reasoning questions based on properties like catalytic behaviour and coloured ions, definitions of lanthanoid contraction and its consequences, and chemical equations for the preparation and oxidising properties of KMnO4 and K2Cr2O7.
Frequently Asked Questions
Why are zinc, cadmium, and mercury not considered true transition elements?
Because they have completely filled d-orbitals (d10) in their ground state as well as in their common oxidation states, which means they do not exhibit typical transition metal properties.
What is lanthanoid contraction and what are its main consequences?
It is the gradual decrease in atomic and ionic radii across the lanthanoid series. Its consequences include the striking similarity in size of elements in the second and third transition series (e.g., Zr and Hf) and the difficulty in separating lanthanoids.
How do you calculate the magnetic moment of a transition metal ion?
By using the spin-only formula mu = sqrt(n(n+2)) Bohr Magnetons (BM), where 'n' represents the number of unpaired electrons in the d-orbitals.
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