Subtopics - d and f-Block Elements (NEET)
Six topic blocks: d-block classification and general properties, f-block lanthanides and actinides, iron compounds, KMnO4 preparation and oxidising properties, K2Cr2O7 and chromyl chloride test, and compounds of copper zinc and silver.
1) d-Block Elements: Classification, Configuration, and General Properties
Transition elements have partially filled d-subshells in their elemental or ionic states. The general configuration is (n-1)d1-10 ns1-2. Four series: 3d (Sc to Zn), 4d (Y to Cd), 5d (La, Hf to Hg), and 6d (incomplete). Anomalous configurations: Cr [Ar]3d5 4s1; Cu [Ar]3d10 4s1. Group 3 (Sc, Y, La, Ac) and Group 12 (Zn, Cd, Hg) are non-typical transition elements. General properties include high melting and boiling points (metallic bonding from d-electrons), variable oxidation states (+2 to +8; highest is +8 for OsO4), formation of coloured ions (d-d transitions), paramagnetism (unpaired d-electrons), complex formation (vacant d-orbitals accept electron pairs from ligands), catalytic activity (variable oxidation states provide alternate low-energy pathways), and alloy formation (similar atomic radii allow substitution in crystal lattice).
2) f-Block Elements: Lanthanides and Actinides
f-block elements (inner transition elements): lanthanides (Ce to Lu, Z=58-71) filling 4f orbitals, and actinides (Th to Lr, Z=90-103) filling 5f orbitals. General configuration: lanthanides [Xe]4f1-14 5d0-1 6s2; actinides [Rn]5f1-14 6d0-1 7s2. Dominant oxidation state is +3 for both series. Lanthanide contraction is the regular decrease in ionic radii from La3+ to Lu3+ due to poor shielding by 4f electrons. Consequences: 4d and 5d elements in the same group have nearly identical radii, basicity of hydroxides decreases La(OH)3 to Lu(OH)3, and separation is only possible by ion exchange. All actinides are radioactive; elements beyond uranium are synthetic.
3) Compounds of Iron
Three key iron compounds for NEET: ferrous sulphate (FeSO4.7H2O, green vitriol), ferric oxide (Fe2O3, haematite), and ferric chloride (FeCl3). Also important: potassium ferrocyanide K4[Fe(CN)6] and potassium ferricyanide K3[Fe(CN)6] for qualitative analysis. FeSO4 is a reducing agent (reduces MnO4- to Mn2+, Cr2O72- to Cr3+). Ring test: FeSO4 + NO forms brown ring of Fe(NO)SO4. Mohr salt FeSO4.(NH4)2SO4.6H2O is a primary standard. FeCl3 is an oxidising agent (oxidises H2S to S, SnCl2 to SnCl4).
4) KMnO4: Preparation, Oxidising Properties, and Volumetric Estimation
KMnO4 is the most important compound of Mn in +7 oxidation state. Prepared by fusing MnO2 with KOH and O2 to form K2MnO4 (green manganate), then oxidising manganate to permanganate either electrolytically or by passing Cl2 or O3. KMnO4 is a powerful oxidising agent whose reduction product depends on the medium: acidic (Mn2+, 5e- transfer), neutral (MnO2, 3e-), alkaline (MnO42- then MnO2, 3e- net). MnO4- has tetrahedral structure (sp3 hybridisation). In volumetric titrations KMnO4 is self-indicating: the endpoint is the first permanent pink colour.
5) K2Cr2O7: Preparation, Oxidising Properties, and Chromyl Chloride Test
K2Cr2O7 (potassium dichromate) is prepared from chromite ore FeCr2O4 by fusion with NaOH/Na2CO3 in air, giving soluble Na2CrO4, followed by acidification to Na2Cr2O7, then metathesis with KCl. It is a powerful oxidising agent: Cr2O72- + 14H+ + 6e- -> 2Cr3+ + 7H2O. The chromyl chloride test identifies Cl- ions: K2Cr2O7 + NaCl + conc. H2SO4 produces red CrO2Cl2 vapours, which on dissolving in NaOH give yellow Na2CrO4; addition of lead acetate gives yellow PbCrO4 precipitate. Chromate-dichromate equilibrium: 2CrO42- + 2H+ = Cr2O72- + H2O (yellow in alkali, orange in acid). CrO42- is tetrahedral; Cr2O72- consists of two corner-sharing tetrahedra.
6) Compounds of Copper, Zinc, and Silver
CuSO4.5H2O (blue vitriol): loses water stepwise on heating; anhydrous CuSO4 is white (test for water). With excess NH3 forms deep blue [Cu(NH3)4]SO4 (Schweitzer reagent, dissolves cellulose). Liberates I2 from KI: 2CuSO4 + 4KI -> Cu2I2 + I2 + 2K2SO4. ZnO (zinc white): amphoteric, dissolves in both acid and alkali, used as white pigment (superior to white lead because ZnS formed with H2S is also white). ZnS is the only white insoluble sulphide. AgNO3 (lunar caustic): prepared by dissolving Ag in dilute HNO3. Stains skin black (reduced to Ag). Forms AgCl, AgBr, AgI with halides. Used in silvering mirrors (reduction by formaldehyde or glucose). AgBr is most photosensitive silver halide (used in photographic films).
d and f-Block Elements Download Notes & Weightage Plan
For each topic in the d and f-Block Elements chapter below, you get (2) the exact resources to download and how to use them, and (3) a simple importance & time plan so NEET students know what to do first and what to revise last.
d-Block Elements: Classification, Configuration, and General Properties
Electronic configurations of 3d, 4d, 5d series with anomalies (Cr, Cu), variable oxidation states, colour from d-d transitions, magnetic moment formula, catalytic properties, complex formation.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Anomalous configurations of Cr and Cu are asked directly. Magnetic moment calculation using spin-only formula is a guaranteed numerical question pattern.
- High-risk Area: Confusing n (number of unpaired electrons) with the total number of d-electrons when applying the spin-only formula. For example, Fe2+ (3d6) has 4 unpaired electrons, not 6.
- Best Practice Style: Half-filled (d5) and fully-filled (d10) configurations give extra exchange energy stability. When 4s2 vs 4s1 is the choice, the element prefers the configuration that achieves d5 or d10.
f-Block Elements: Lanthanides and Actinides
Lanthanides (4f series) and actinides (5f series), dominant +3 state, lanthanide contraction mechanism and consequences, actinide variable OS, comparison of two series.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Lanthanide contraction and its consequences (especially 4d-5d size similarity) are the most tested facts. Ce4+ as oxidising agent and Eu2+ as reducing agent are classic questions.
- High-risk Area: Forgetting that lanthanide contraction affects 5d elements (Hf has nearly same radius as Zr because of the 4f contraction). Also confusing lanthanide and actinide contraction causes.
- Best Practice Style: 4f orbitals shield poorly because of their diffuse radial distribution. Each added 4f electron barely screens the increased nuclear charge, so outer electrons are pulled closer.
FeSO4.7H2O (green vitriol), Fe2O3 (haematite), FeCl3, K4[Fe(CN)6] (ferrocyanide), K3[Fe(CN)6] (ferricyanide). Preparation, properties, and qualitative analysis tests.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Ring test (FeSO4 + NO = brown Fe(NO)SO4) and Prussian blue test (Fe3+ + K4[Fe(CN)6] = blue precipitate) are highest yield.
- High-risk Area: Confusing Prussian blue and Turnbull blue. Modern evidence shows both are the same compound (Fe4[Fe(CN)6]3). Also confusing the oxidation states in ferrocyanide (Fe2+) vs ferricyanide (Fe3+).
- Best Practice Style: Ferrocyanide = ferro = iron(II) inside. Ferricyanide = ferri = iron(III) inside. The prefix tells you the oxidation state of the central Fe.
KMnO4: Preparation, Oxidising Properties, and Volumetric Estimation
KMnO4 preparation from MnO2, oxidising behaviour in acidic/neutral/alkaline media, self-indicator in permanganimetry, tetrahedral MnO4- structure.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: The acidic-medium half-equation (MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O) is the single most important equation. Media-dependent reduction product is the most common trap.
- High-risk Area: Applying the acidic-medium equation in alkaline conditions. In alkaline medium, MnO4- gives MnO2 (brown), not Mn2+ (colourless). The 5-electron transfer applies only in acid.
- Best Practice Style: Acid = 5 electrons = Mn2+ (colourless). No acid = 3 electrons = MnO2 (brown precipitate). Map the medium to the colour change.
K2Cr2O7: Preparation, Oxidising Properties, and Chromyl Chloride Test
K2Cr2O7 from chromite ore, oxidising behaviour, chromyl chloride test for Cl-, chromate-dichromate equilibrium, structures.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Chromyl chloride test (red CrO2Cl2 vapours confirmed by yellow PbCrO4) is the most tested fact. Chromate (yellow, alkaline) vs dichromate (orange, acidic) interconversion is a frequent option-pair in MCQs.
- High-risk Area: Confusing the chromyl chloride confirmatory precipitate (yellow PbCrO4) with white PbCl2. Students mix up the two lead salt tests.
- Best Practice Style: Chromyl chloride test confirms Cl- by converting it to CrO42- and then detecting CrO42- as PbCrO4. The detection target is chromate, not chloride directly.
Compounds of Copper, Zinc, and Silver
CuSO4.5H2O dehydration and Schweitzer reagent, ZnO amphoteric nature, ZnS phosphorescence, AgNO3 (lunar caustic) and silvering, AgBr photosensitivity.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Anhydrous CuSO4 (white) turning blue with water is a classic test question. AgBr as the most photosensitive silver halide appears in photography-based questions.
- High-risk Area: Thinking CuSO4.5H2O is used to test for water. It is already hydrated. Only anhydrous CuSO4 (white) shows the colour change upon exposure to moisture.
- Best Practice Style: White to blue = water present (anhydrous CuSO4). Blue to white = heating removes water. The test works because of the dramatic colour change at the coordination sphere level.
d and f-Block Elements Chapter NEET Traps & Common Mistakes (Topic-Wise)
Each subtopic below is of the d and f-Block Elements chapter and shows what NEET students usually do wrong in NEET examination, a short example of the mistake, and how NEET frames the question to trick you with close options are given below.
Mistake Snapshot (What Students Do Wrong)
- Using total d-electrons as n: Fe2+ has 3d6 configuration. Students take n=6 in the spin-only formula instead of n=4 (the actual number of unpaired electrons after applying Hund rule to 5 d-orbitals).
- Forgetting pairing in d6: In 3d6, five electrons fill the five d-orbitals singly, and the sixth electron pairs with one. This gives 4 unpaired electrons, not 6.
Fe2+ has configuration [Ar]3d6. Filling 5 d-orbitals singly accounts for 5 electrons. The 6th electron pairs in one orbital. Unpaired electrons = 4. Magnetic moment = sqrt(4 x 6) = sqrt(24) = 4.90 BM.
How NEET Frames The Trap
NEET gives a d-electron count and asks for the magnetic moment.
Q. The spin-only magnetic moment of Fe2+ ion (3d6 configuration) in Bohr magnetons is approximately
A. 4.90 B. 6.93 C. 5.92 D. 2.83
Trick: 4.90 BM (Option A): Fe2+ (3d6) has 4 unpaired electrons, mu = sqrt(4(4+2)) = sqrt(24) = 4.90 BM. Option B (6.93) incorrectly uses n=6 (all d-electrons). Option C (5.92) uses n=5 (Mn2+ value, not Fe2+).
Mistake Snapshot (What Students Do Wrong)
- Applying acidic-medium equation everywhere: Students memorise MnO4- -> Mn2+ (5e-) and use it in neutral or alkaline conditions. In alkaline or neutral medium, MnO4- is reduced to MnO2 (3e-).
- Writing non-standard manganese products: Some students invent products like Mn2O7 or MnO3 that do not correspond to any standard half-equation for permanganate reduction.
KMnO4 added to alkaline KI solution: MnO4- + 2H2O + 3e- -> MnO2 + 4OH-. The brown precipitate of MnO2 forms, not the colourless Mn2+ that would appear in acidic medium.
How NEET Frames The Trap
NEET specifies the medium (acidic, neutral, or alkaline) and asks for the reduction product of KMnO4.
Q. When KMnO4 acts as an oxidising agent in neutral aqueous medium, the manganese-containing product is
A. MnO2 B. Mn2+ C. MnO42- D. Mn2O3
Trick: MnO2 (Option A): In neutral medium, MnO4- + 2H2O + 3e- -> MnO2 + 4OH-. Mn2+ (Option B) is the product only in acidic medium (5e- transfer). MnO42- is manganate (intermediate in alkaline medium, not the final product).
Mistake Snapshot (What Students Do Wrong)
- Expecting white PbCl2: Students associate lead acetate with chloride testing and expect white PbCl2. In the chromyl chloride test, lead acetate reacts with chromate (not chloride) to give yellow PbCrO4.
- Forgetting the CrO2Cl2 dissolution step: Students skip the step where red CrO2Cl2 vapours are dissolved in NaOH to form Na2CrO4 before adding lead acetate.
Red CrO2Cl2 vapours dissolved in NaOH give yellow Na2CrO4 solution. Lead acetate is added: Pb2+ + CrO42- -> PbCrO4 (yellow precipitate). The confirmatory precipitate is yellow lead chromate PbCrO4, not white lead chloride PbCl2.
How NEET Frames The Trap
NEET describes the chromyl chloride test and asks for the confirmatory precipitate colour or formula.
Q. In the chromyl chloride test for chloride ions, the confirmatory yellow precipitate formed on adding lead acetate to the dissolved CrO2Cl2 solution is
A. PbCrO4 B. PbCl2 C. PbSO4 D. Pb(OH)2
Trick: PbCrO4 (Option A): Yellow lead chromate. The CrO2Cl2 vapours hydrolyse to give CrO42- in alkaline solution. PbCl2 (Option B) is a white precipitate from a completely different test. The chromyl chloride test detects Cl- indirectly through chromate formation.
Mistake Snapshot (What Students Do Wrong)
- Equating d-block with transition: Students assume all d-block elements are transition elements. Zn, Cd, and Hg have d10 configuration in both elemental and common ionic states, so they do not meet the strict definition.
- Ignoring the ionic state criterion: Cu is [Ar]3d10 4s1 as an element (d10) but Cu2+ is [Ar]3d9 (partially filled d), so Cu qualifies as a transition element. Zn2+ remains d10, so Zn does not.
Zn [Ar]3d10 4s2. Zn2+ [Ar]3d10. Both elemental Zn and Zn2+ have completely filled d-orbitals. Therefore Zn is a d-block element but not a true transition element.
How NEET Frames The Trap
NEET asks whether Zn (or Cd or Hg) is a transition element.
Q. Which of the following Group 12 elements qualifies as a true transition element according to IUPAC definition?
A. None of Zn, Cd, Hg B. All of Zn, Cd, Hg C. Only Hg D. Only Zn
Trick: None (Option A): Zn2+ (3d10), Cd2+ (4d10), and Hg2+ (5d10) all have completely filled d-orbitals. True transition elements must have a partially filled d-subshell in at least one commonly stable oxidation state. All three Group 12 elements fail this criterion.
Mistake Snapshot (What Students Do Wrong)
- Selecting pentahydrate as the testing reagent: Students remember CuSO4 is blue and choose CuSO4.5H2O for the water test. The pentahydrate is already hydrated and shows no colour change when exposed to water.
- Confusing dehydration temperatures: CuSO4.5H2O -> CuSO4.3H2O on simple exposure; CuSO4.H2O at 100 C; anhydrous CuSO4 (white) at 230 C. Only the anhydrous form is the testing reagent.
Anhydrous CuSO4 is a white powder. On adding a drop of water, it turns blue (reforms the hydrated pentahydrate). This white-to-blue colour change is the standard qualitative test for presence of water or moisture.
How NEET Frames The Trap
NEET asks which form of copper sulphate is used to detect the presence of water.
Q. The reagent used to detect the presence of water by a characteristic colour change is
A. Anhydrous CuSO4 B. CuSO4.5H2O C. CuSO4.H2O D. CuCl2
Trick: Anhydrous CuSO4 (Option A): White powder turns blue on absorbing water. CuSO4.5H2O (Option B) is already blue and cannot show a visible colour change. The test relies on the white (anhydrous) -> blue (hydrated) transition.