313_Chemistry_Eng_Lesson21.pdf). Content covers sections 21.1–21.7.Between the s- and p-blocks sit the d-block (transition) elements, where the (n−1)d subshell fills. The first series is Sc–Cu (3d). Separately at the bottom of the table, the f-block (inner transition) elements fill 4f (lanthanoids) and 5f (actinoids). This lesson covers definition and configuration, physical and characteristic properties of 3d metals, preparation and redox chemistry of K₂Cr₂O₇ and KMnO₄, lanthanoid contraction and oxidation states, and a comparison of lanthanoids with actinoids.
Transition elements have a partially filled d-subshell in the atom or in a common ion. General configuration: (n−1)d¹–¹⁰ ns¹–². Four series: 3d (Sc–Cu), 4d, 5d, 6d. Cu, Ag, Au count as transition metals because Cu²⁺ (3d⁹), Ag²⁺, Au³⁺ have incomplete d shells. Zn, Cd, Hg have d¹⁰ in atom and ions — not transition elements, though often discussed with the d-block.
Energy of 3d falls below 4p after Ca, so electrons enter 3d. Half-filled and full d shells are extra stable → Cr and Cu have only one 4s electron. Occurrence: few free (Au, Pt); most as oxides, sulphides, carbonates.
Typical metals: high tensile strength, ductility, conductivity, lustre. High m.p./b.p. (usually >1356 K) from small size and strong metallic bonding involving d electrons. High density; maxima around Groups 8–10. Hard (except Zn, Cd, Hg). Atomic radii decrease across the series (poor d shielding raises Z_eff) then rise slightly near the end. 4d and 5d metals of a group are similar in size because of lanthanoid contraction.
Variable oxidation states: both ns and (n−1)d electrons can bond. After Sc, +2 is very common (loss of 4s). High OS with F and O (Mn +7 in MnO₄⁻, Cr +6 in Cr₂O₇²⁻). Higher OS oxides more acidic (MnO basic; Mn₂O₇ acidic). High-OS compounds are strong oxidants.
Magnetic properties: unpaired electrons → paramagnetism. Spin-only moment:
Colour: white light partially absorbed by d–d transitions; complementary colour observed (CuSO₄ blue). d⁰ and d¹⁰ ions usually colourless (Sc³⁺, Ti⁴⁺, Zn²⁺, Cu⁺).
Alloys & interstitial compounds: similar atomic sizes → brass (Cu–Zn), bronze (Cu–Sn), stainless steel. Small H, C, N atoms in lattice voids → hard interstitial compounds (steel hardness from carbon).
Complex formation: small size, high charge, vacant d orbitals accept ligand pairs (L22).
Catalysis: variable OS and surface adsorption. Examples: V₂O₅ (Contact process), Fe (Haber), Ni (hydrogenation), Pd/Cu (Wacker). Fe³⁺ catalyses I⁻ + S₂O₈²⁻ by cycling Fe³⁺/Fe²⁺.
From chromite FeO·Cr₂O₃: roast with Na₂CO₃ + air (+ CaO for porosity) → Na₂CrO₄ → acidify → Na₂Cr₂O₇ → metathesis with KCl → orange-red K₂Cr₂O₇.
With NaCl + conc. H₂SO₄ → red chromyl chloride CrO₂Cl₂ (confirmatory test for chloride). Uses: volumetric oxidant; chrome alum for tanning/dyeing.
Ionic oxidations to memorise: Cr₂O₇²⁻ + 6Fe²⁺ + 14H⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H₂O; Cr₂O₇²⁻ + 6I⁻ + 14H⁺ → 2Cr³⁺ + 3I₂ + 7H₂O; Cr₂O₇²⁻ + 3SO₂ + … → Cr³⁺ + SO₄²⁻. Oxidation number of Cr is +6 in both K₂CrO₄ and K₂Cr₂O₇.
From pyrolusite MnO₂: fuse with KOH/air → green K₂MnO₄ → oxidise (Cl₂, O₃ or anodic oxidation) → purple KMnO₄. Manganate disproportionates in acid: 3MnO₄²⁻ + 4H⁺ → 2MnO₄⁻ + MnO₂ + 2H₂O.
Acidic: oxidises Fe²⁺, SO₂, C₂O₄²⁻. Neutral: Mn²⁺ → MnO₂; H₂S → S. Alkaline: I⁻ → IO₃⁻; ethene → ethylene glycol. Uses: disinfectant (wells, mouthwash), volumetric standard for Fe(II), oxalate, H₂O₂. Heat: 2KMnO₄ → K₂MnO₄ + MnO₂ + O₂.
La–Lu (14 + La): filling of 4f. Config mostly [Xe] 4fⁿ 6s² (La, Gd, Lu have 5d¹). Extremely similar chemically; older name “rare earths” is misleading.
Lanthanoid contraction: 4f electrons shield poorly → gradual decrease in atomic/ionic radii from La³⁺ to Lu³⁺. Consequence: Zr and Hf nearly identical size and chemistry; Hf denser than Zr.
Oxidation states: characteristic +3. +2/+4 when f⁰ (Ce⁴⁺), f⁷ (Eu²⁺, Tb⁴⁺) or f¹⁴ (Yb²⁺) stabilised. Highly electropositive; compounds largely ionic. More mutual resemblance than d-block metals because +3 dominates.
Ac–Lr: filling of 5f (with early members mixing 6d). Almost all radioactive (Pm is the only radioactive lanthanoid). +3 common but Th, U, Np, Pu show higher states; Np/Pu up to +7; oxocations UO₂²⁺, PuO₂²⁺. Am²⁺ (f⁷) known.
Ln vs An: both show contraction and +3 prominence; An more radioactive, wider OS range, better complexation, form oxocations, more basic compounds; 5f less effectively screened and closer in energy to 6d than 4f to 5d.
High-yield: definition of transition metal (Zn vs Cu); Cr/Cu configs; μ formula; colour origin; K₂Cr₂O₇ and KMnO₄ preparation outlines and acidic half-reactions; chromate–dichromate equilibrium; chromyl chloride; lanthanoid contraction and Zr/Hf; Ln +3 and special +2/+4; Ln vs An differences.
Connects to L20 (V₂O₅ catalysis), L13 (redox half-cells), L22 (complexes). Practice balancing dichromate and permanganate ionic equations — they appear constantly in volumetric and redox questions.
Intext-style checks: why Cu is transition but Zn is not; μ for V⁴⁺, Cr³⁺, Ni²⁺; coloured vs colourless ions; chromite and pyrolusite formulae; dichromate half-reaction; KMnO₄ in three media; lanthanoid contraction and Zr/Hf; Ln +3; An vs Ln differences. Alloys to name: brass, bronze, stainless steel. Catalysts: Fe, Ni, V₂O₅, PdCl₂.
Most exam-important points from this chapter:
Partial d in atom/ion. Config (n−1)d ns. Cr/Cu exceptions. Zn not transition. High m.p., density, variable OS.
μ = √[n(n+2)]. Unpaired e⁻ → paramagnetic & often coloured (d–d). d⁰/d¹⁰ colourless/diamagnetic.
From chromite. Acid: 6e⁻ to Cr³⁺. Orange⇌yellow with alkali. Chromyl chloride tests Cl⁻. Volumetric oxidant.
From MnO₂ via manganate. Acid 5e⁻→Mn²⁺; neutral/alkaline → MnO₂. Disinfectant & volumetric reagent.
Ln: 4f, +3, contraction → Zr/Hf similar. An: 5f, radioactive, higher OS, oxocations, more complex chemistry.
Extracted from NIOS Chemistry (313) board exam papers in your PDF. Chapter L21 — d-Block and f-Block Elements only. Use Model Answer for marking points; Explanation for concept clarity.
5 question(s) · Sources: 313/MAY/205A, 313/MAY/205B, 313/MAY/205C, 313/TUS/105A
PYQ1. Read the passage given below and answer the following questions : Most of the compounds of d-block elements are coloured or they give coloured solution when dissolved in water. This is generally associated with incomplete (n – 1)d subshell of the transition metal. If red portion of white light is absorbed by a substance, it would appear blue. Identify the incorrect statement from the following : (i) An energy transition of electrons takes place in transition metal ions which absorb some of the energy of visible light. (ii) The colour of the ions is due to the presence of all paired electrons in them. (iii) Blue is the complementary colour of red. (iv) In transition metals, the energy difference between the various d-orbitals is in the same order of magnitude as the energies of radiation of white light. What is the colour of hexahydrated form of ferric ions?
Model Answer
State the precise definition from the L21 notes in 1–2 sentences, include formula/example if marks ≥ 2, and avoid extra theory beyond the ask.
Explanation
Definition questions score for accuracy of wording + one supporting point/example. Do not write full chapter summaries.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/MAY/205A · Q23 · 2 mark(s) · L21.
PYQ2. Read the passage given below and answer the following questions : Most of the compounds of d-block elements are coloured or they give coloured solution when dissolved in water. This is generally associated with incomplete (n – 1)d subshell of the transition metal. If red portion of white light is absorbed by a substance, it would appear blue. Identify the incorrect statement from the following : (i) An energy transition of electrons takes place in transition metal ions which absorb some of the energy of visible light. (ii) The colour of the ions is due to the presence of all paired electrons in them. (iii) Blue is the complementary colour of red. (iv) In transition metals, the energy difference between the various d-orbitals is in the same order of magnitude as the energies of radiation of white light. What is the colour of hexahydrated form of ferric ions?
Model Answer
State the precise definition from the L21 notes in 1–2 sentences, include formula/example if marks ≥ 2, and avoid extra theory beyond the ask.
Explanation
Definition questions score for accuracy of wording + one supporting point/example. Do not write full chapter summaries.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/MAY/205B · Q27 · 2 mark(s) · L21.
PYQ3. Read the passage given below and answer the following questions : Most of the compounds of d-block elements are coloured or they give coloured solution when dissolved in water. This is generally associated with incomplete (n – 1)d subshell of the transition metal. If red portion of white light is absorbed by a substance, it would appear blue. Identify the incorrect statement from the following : (i) An energy transition of electrons takes place in transition metal ions which absorb some of the energy of visible light. (ii) The colour of the ions is due to the presence of all paired electrons in them. (iii) Blue is the complementary colour of red. (iv) In transition metals, the energy difference between the various d-orbitals is in the same order of magnitude as the energies of radiation of white light. What is the colour of hexahydrated form of ferric ions?
Model Answer
State the precise definition from the L21 notes in 1–2 sentences, include formula/example if marks ≥ 2, and avoid extra theory beyond the ask.
Explanation
Definition questions score for accuracy of wording + one supporting point/example. Do not write full chapter summaries.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/MAY/205C · Q25 · 2 mark(s) · L21.
PYQ4. Write True (T) for correct statement and False (F) for incorrect statement (out of four attempt any two) : Copper(I) compounds are white and diamagnetic while copper(II) compounds are coloured and paramagnetic. The common oxidation state of Cu, Ag and Au is +2. Scandium does not exhibit variable oxidation state in its compounds. Among Al, Zn, Mg and Fe, the densest element is Fe. ghr
Model Answer
Answer using key concepts from L21 (definitions, equations, and one example where useful). Stay within the suggested word range for a 2-mark NIOS question.
Explanation
Cross-check with L21 notes. Structure: definition/law → working → conclusion. Partial marks for correct equations even if explanation is short.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/TUS/105A · Q23 · 2 mark(s) · L21.
PYQ5. Give reason for the following : Transition elements have higher density as compared to s-block elements. Transition metals show high melting and boiling points
Model Answer
Present a clear comparison in 2–3 points (definition / structure / property / example). Use a table style in prose: A vs B for each criterion.
Explanation
Comparison answers need parallel points. Award marks for each distinct difference.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/MAY/205A · Q37 · 2 mark(s) · L21.
Six problems spanning this chapter’s NIOS syllabus. Every question is built from the notes and formula sheet: solve with equations first, then read the formal textbook-style write-up, the easy explanation, and the topic in depth (formulas, meaning, exam tips). If the question says draw, a labelled pencil sketch is provided. Explanations open by default.
Define transition elements and give one characteristic property.
Final answer: Incomplete d; coloured ions / variable OS
Transition metals show variable oxidation states and complex formation.
Working formulas: (n−1)d ns configuration. State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Middle of the table metals with partly filled d orbitals.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Zn sometimes excluded (d¹⁰).
Linked to chapter notes (L21). Remember: (n−1)d ns configuration. Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (n−1)d ns configuration before substituting. Keep three significant figures until the end when data allow.
Why are many transition metal ions coloured?
Final answer: d–d transitions
Absorption of visible photons promotes d electrons between split levels.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Ion absorbs some colours and we see the complementary colour.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
d⁰ and d¹⁰ often colourless.
Linked to chapter notes (L21). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Why do transition metals show variable oxidation states?
Final answer: ns and (n−1)d both available
Successive ionisation energies allow multiple stable OS.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
They can lose different numbers of electrons fairly easily.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Mn shows OS from +2 to +7.
Linked to chapter notes (L21). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Give one industrial process catalysed by a transition metal/compound.
Final answer: e.g. Fe in Haber process
Variable OS and surface adsorption enable catalysis.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Metal surface holds reactants and helps them react faster.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Enzymes also use transition metals in biology.
Linked to chapter notes (L21). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What is lanthanoid contraction and one consequence?
Final answer: Size decrease across 4f series
Poor shielding by 4f electrons causes gradual contraction.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Atoms get slightly smaller across the f-block.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Zr/Hf similar chemistry.
Linked to chapter notes (L21). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What are interstitial compounds of transition metals?
Final answer: Small atoms in metal voids
Non-stoichiometric hard materials important as steels/carbides.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Carbon squeezes into iron lattice—steel properties change.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Retain metallic conductivity often.
Linked to chapter notes (L21). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.