Class 12 Chemistry - HARYANA
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 BSEH students, mastering this chapter is essential as it covers important periodic trends such as variable oxidation states, coloured ion formation, catalytic properties, and magnetic behavior of d-block elements, alongside the similarities and lanthanoid contraction of f-block elements. Questions from this chapter frequently appear in board exams as reasoning-based problems, chemical equations, and direct numerical or conceptual queries, carrying significant weightage.
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 common oxidation states.
Variable Oxidation States
Transition metals 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.
Coloured Ions
Most transition metal ions are coloured due to d-d electronic transitions, where an electron absorbs visible light to jump from one d-orbital to another.
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 Properties
Transition metal ions exhibit paramagnetism due to the presence of unpaired electrons, which increases with the number of unpaired d-electrons.
Important Formulas
Board Exam Info
In the Haryana Board (BSEH) Class 12 Chemistry examination, this chapter typically carries around 4 to 6 marks. Students can expect 1-mark objective questions, short-answer reasoning questions (such as why transition metals act as catalysts or why Zn, Cd, and Hg are not true transition elements), and occasional balanced chemical equations for the preparation of KMnO4 or K2Cr2O7.
Frequently Asked Questions
Why are Zn, Cd, and Hg not considered transition elements?
Because they have completely filled d-orbitals (d10 configuration) in their ground state as well as in their common oxidation states, which means they do not show typical transition metal properties.
What is Lanthanoid Contraction and what are its consequences?
It is the gradual decrease in atomic/ionic radii across the lanthanoid series. Its main consequences include the near-identical radii of 4d and 5d series elements (e.g., Zr and Hf) and difficulty in separating lanthanoids.
Why do transition metals form coordination compounds?
Transition metals have small atomic sizes, high nuclear charges, and vacant d-orbitals of suitable energy, which allow them to accept lone pairs of electrons from ligands.
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