# The d- and f-Block Elements, Class 12 Chemistry | SwaVid The d- and f-Block Elements, NCERT Class 12 Chemistry: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-12/chemistry/chapter/the-d-and-f-block-elements Source: https://www.swavid.com/cbse/class-12/chemistry/chapter/the-d-and-f-block-elements # The d- and f-Block Elements ## Formulas and definitions ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 12 Chemistry on SwaVid ### Position and definition of d-block elements ### General physical and chemical trends ### Oxidation states and standard electrode potentials ### Catalytic and magnetic properties ### Potassium dichromate and potassium permanganate ### The f-block elements and lanthanoid contraction ### Next chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 12 › Chemistry › The d- and f-Block Elements Notes written by SwaVid from the NCERT textbook. Class 12 Chemistry, Unit 4. Key ideas, formulas and common mistakes. CBSE prints 7 marks for Unit 4, not for this chapter alone. Short answer. This chapter covers the electronic configurations, trends in properties, and chemical reactivity of transition elements and inner transition elements. Students learn how incompletely filled d and f orbitals govern variable oxidation states, catalytic behavior, complex formation, and magnetic character. Source: NCERT Chemistry Part I (Reprint 2026-27) , Unit 4, The d- and f-Block Elements The d-block elements occupy groups 3 to 12 of the periodic table. A transition element is defined as an element that has an incompletely filled d subshell in its ground state or in any of its common oxidation states. Zinc, cadmium, and mercury have fully filled (n-1)d¹⁰ configurations in both ground and common oxidation states, so they are not regarded as typical transition elements. Transition metals display high enthalpies of atomisation, high melting points, and high densities due to strong interatomic metallic bonding involving both (n-1)d and ns electrons. Atomic and ionic radii decrease across a series due to increasing effective nuclear charge, but the decrease levels off toward the end because of d-d electron repulsion. Transition metals exhibit variable oxidation states because the energy difference between (n-1)d and ns orbitals is very small. In the 3d series, manganese shows the highest oxidation state of +7. Standard reduction potentials (E° values) depend on a balance among enthalpy of atomisation, ionisation enthalpy, and hydration enthalpy. Paramagnetism arises from unpaired electrons, and the spin-only magnetic moment is given by μ = √(n(n + 2)) BM. Transition elements act as effective catalysts because they show variable oxidation states, provide suitable reaction surfaces, and can form unstable reaction intermediates. Potassium dichromate (K₂Cr₂O₇) is prepared from chromite ore and acts as a strong oxidising agent in acidic medium, where Cr₂O₇²⁻ is reduced to Cr³⁺. Potassium permanganate (KMnO₄) is prepared from pyrolusite ore (MnO₂) via manganate (MnO₄²⁻), and oxidises oxalates, iron(II), and nitrites in acidic solution while being reduced to Mn²⁺. The f-block consists of lanthanoids (4f series) and actinoids (5f series). The steady decrease in atomic and ionic radii from lanthanum to lutetium is called lanthanoid contraction, caused by the poor shielding of 4f electrons. Actinoids display a wider range of oxidation states than lanthanoids because 5f, 6d, and 7s levels are close in energy. Try each question first. Then tap it to see the answer. Atomic number Z = 25 gives the configuration of M as [Ar] 3d⁵ 4s². For M²⁺, two 4s electrons are lost, leaving [Ar] 3d⁵, so n = 5 unpaired electrons. μ = √(n(n + 2)) = √(5 × (5 + 2)) = √35 ≈ 5.92 BM. 5.92 BM Sc³⁺ has the configuration [Ar] 3d⁰, with zero d electrons, so d-d transitions cannot occur. Ti³⁺ has the configuration [Ar] 3d¹, with one unpaired d electron available for d-d transition upon absorbing visible light. Sc³⁺ lacks d electrons for d-d transitions; Ti³⁺ has one d electron and absorbs visible light. Dichromate half-reaction: Cr₂O₇²⁻ + 14 H⁺ + 6 e⁻ → 2 Cr³⁺ + 7 H₂O. Iron half-reaction: Fe²⁺ → Fe³⁺ + e⁻. Multiply the Fe²⁺ half-reaction by 6 to balance electrons: 1 mole of Cr₂O₇²⁻ reacts with 6 moles of Fe²⁺. 6 moles Coordination Compounds . Electrochemistry . The 10 chapters of Class 12 Chemistry . CBSE does not give marks to one chapter. It prints 7 marks for Unit 4, d- and f-Block Elements, which includes The d- and f-Block Elements. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Coordination Compounds. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Unit 4 NCERT book - 7 marks, Unit 4 - 3 quick checks - Classifying Zn, Cd, and Hg as transition elements . Remember that transition elements must have an incompletely filled d subshell in their ground state or common oxidation state; Zn, Cd, and Hg have full d¹⁰ subshells in both states. - Attributing the similarity of Zr and Hf radii to their positions in the same group . State that zirconium (4d) and hafnium (5d) have almost identical atomic radii because of the lanthanoid contraction, which intervenes between them. - Using nitric acid or hydrochloric acid to acidify KMnO₄ solutions in titrations . Only dilute H₂SO₄ must be used; HNO₃ is an oxidising agent itself, and HCl is oxidised to chlorine gas by KMnO₄. - Confusing the number of unpaired electrons in Mn²⁺ and Fe²⁺ . Write the electronic configurations carefully: Mn²⁺ is 3d⁵ with 5 unpaired electrons, whereas Fe²⁺ is 3d⁶ with 4 unpaired electrons. ## Key Links - [CBSE](https://www.swavid.com/cbse) - [Class 12](https://www.swavid.com/cbse/class-12) - [Chemistry](https://www.swavid.com/cbse/class-12/chemistry/chapters) - [Start free →](https://www.swavid.com/signup) - [All 10 chapters](https://www.swavid.com/cbse/class-12/chemistry/chapters) - [NCERT Chemistry Part I (Reprint 2026-27)](https://ncert.nic.in/textbook.php) - [Open notes](https://www.swavid.com/cbse/class-12/chemistry/chapter/coordination-compounds) - [Open notes](https://www.swavid.com/cbse/class-12/chemistry/chapter/electrochemistry) - [Class 12 Chemistry](https://www.swavid.com/cbse/class-12/chemistry/chapters) - [Start free →](https://www.swavid.com/signup)