Class 12 Chemistry - PUNJAB
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 located in the middle and bottom of the periodic table. For Punjab (PSEB) board exams, students must master key properties such as variable oxidation states, coloured ion formation, catalytic activity, magnetic properties, and complex compound formation in d-block elements. Additionally, the chapter covers the lanthanoid and actinoid series of f-block elements, highlighting phenomena like lanthanoid contraction and its consequences. A strong grasp of trends and electronic configurations is essential for scoring high marks in board examinations.
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 comprising groups 3 to 12.
Variable Oxidation States
Due to very small energy differences between (n-1)d and ns orbitals, d-block elements exhibit multiple oxidation states by losing electrons from both shells.
Colour and Magnetic Properties
Transition metal ions are often coloured due to d-d electron transitions absorbing visible light, and they show paramagnetism due to the presence of unpaired d-electrons.
Lanthanoid Contraction
The steady decrease in atomic and ionic radii along the lanthanoid series due to poor shielding of nuclear charge by 4f electrons.
Interstitial Compounds
Compounds formed when small atoms like H, C, or N are trapped inside the crystal lattices of transition metals, making them hard and rigid.
Important Formulas
Board Exam Info
In the Punjab (PSEB) Class 12 Chemistry board exam, this chapter typically carries around 4 to 6 marks. Questions frequently include reasoning-type questions about variable oxidation states, colour of ions, catalytic behaviour, and explanations regarding lanthanoid contraction and its consequences.
Frequently Asked Questions
Why do transition elements act as good catalysts?
They provide a large surface area with free valencies and can exhibit variable oxidation states to form unstable intermediate compounds during reactions.
What is lanthanoid contraction and what causes it?
It is the gradual decrease in size of lanthanoid ions from La to Lu, caused by the poor shielding effect of 4f electrons which fails to balance the increasing nuclear charge.
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 typical transition properties.
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