Class 12 Chemistry - MP
The d- and f-Block Elements
The chapter 'The d- and f-Block Elements' in Class 12 Chemistry explores the transition elements (d-block) and inner transition elements (f-block, including lanthanoids and actinoids). Students learn about their general characteristics, electronic configurations, variable oxidation states, coloured ion formation, catalytic properties, and alloy formation. Special emphasis is placed on trends like atomic and ionic radii, ionization enthalpies, and the phenomenon of lanthanoid contraction. For Madhya Pradesh Board (MPBSE) exams, this is a high-scoring chapter with direct questions on reasoning, properties, and important compounds like potassium dichromate and potassium permanganate.
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.
Lanthanoid Contraction
The steady decrease in atomic and ionic radii of lanthanoids with increasing atomic number due to poor shielding of nuclear charge by 4f electrons.
Variable Oxidation States
d-Block elements exhibit multiple oxidation states because of the very small energy gap between $(n-1)d$ and $ns$ orbitals.
Magnetic Moment
Most transition metal ions are paramagnetic due to the presence of 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, making them hard and rigid.
Inner Transition Elements (f-Block)
Elements in which the last electron enters the f-orbital, divided into lanthanoids (4f-series) and actinoids (5f-series).
Important Formulas
Board Exam Info
In the MPBSE Class 12 Chemistry board exam, this chapter typically carries around 4 to 6 marks. Questions frequently include short-answer 'give reasons' type questions based on lanthanoid contraction, coloured ions, catalytic properties, and chemical equations for the preparation and properties of potassium permanganate and potassium dichromate.
Frequently Asked Questions
Why do transition metals form coloured compounds?
Transition metal ions form coloured compounds due to d-d electron transition, where electrons absorb visible light to jump from lower to higher energy d-orbitals.
What is lanthanoid contraction and what are its consequences?
It is the gradual decrease in size of lanthanoid ions. Its main consequence is that the radii of 4d and 5d series elements are nearly identical, making them difficult to separate.
Why are Zn, Cd, and Hg not considered true transition elements?
Because they have completely filled d-orbitals (d10 configuration) in their ground state as well as in their common oxidation states, lacking typical transition properties.
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