🧪 outer transition elements (d-block) · extended master notes

Definition: Elements with partially occupied d-orbitals in atomic or ionic state → outer transition / d-block elements. Positioned between s and p blocks. Key because of versatile oxidation states, catalytic activity, alloy formation, colour, complex formation, magnetic behaviour, electrical conductivity.

Four series:

• 3d-series: Period 4, Sc (21) to Zn (30).
• 4d-series: Period 5, Y (39) to Cd (48).
• 5d-series: Period 6, La (57) to Hg (80).
• 6d-series: Ac (89) to Cn (112).

Chromium (Z=24): expected [Ar] 4s² 3d⁴ but actual [Ar] 4s¹ 3d⁵ (half‑filled d⁵ stability).

Copper (Z=29): expected [Ar] 4s² 3d⁹ but actual [Ar] 4s¹ 3d¹⁰ (completely filled d¹⁰).

Definition: Energy required to separate constituents of a bound system. In d‑block, binding energy is higher due to strong attraction of outermost d electrons. Across a period: increases due to increasing nuclear charge and decreasing atomic radius. Down a group: decreases because atomic size and shielding reduce effective nuclear charge.

Range from +1 to +7. Due to very small energy difference between (n‑1)d and ns orbitals → both electrons participate. Common oxidation state +2; highest +7 (Mn). Increase from Sc to Mn, then decrease to Zn.

Examples: Sc (+3), Ti (+3,+4), V (+2 to +5), Cr (+2,+3,+6), Mn (+2,+4,+6,+7), Fe (+2,+3), Co (+2,+3), Ni (+2), Cu (+1,+2), Zn (+2).

• Order: ligands alphabetically (ignoring prefix), then metal.
• Anionic ligands: end in “O” (fluoro, chloro, bromo, thiocyanato, amido, oxalato, carbonato, hydroxo, thiosulphato).
• Neutral ligands: usually unchanged (amine, carbonyl, nitrosyl), but water = “aquo”.
• Number of ligands: inorganic → di‑, tri‑, tetra‑, penta‑, hexa‑ ; organic ligands → bis‑, tris‑, tetrakis‑.
• Anionic complex: metal name with suffix “‑ate” (remove ‑ium/‑um). Cationic/neutral complexes: English name.

Examples from document:

[Cu(NH₃)₄]SO₄ → tetraaminecopper(II) sulphate

[Cr(H₂O)₄Cl₂]NO₃ → tetraaquodichlorochromium(III) nitrate

K₄[Fe(CN)₆] → potassium hexacyanoferrate(II)

[Pt(NH₂‑CH₂‑CH₂‑NH₂)₃]Cl₄ → tris(ethylenediamine)platinum(IV) chloride

[Co(NH₃)₃(NO₂)₃] → triaminetrinitrocobalt(III)

[Zn(OH)₄]²⁻ → tetrahydroxozincate(II) ion

[Cu(en)₂]²⁺ → bis(ethylenediamine)copper(II) ion

Chromium: silvery grey, 3d⁵4s¹. Oxidation states +2,+3,+4,+5,+6. Lower states = reducing agent; higher = oxidising agent.

Reactions:
2Cr(s) + 6HCl(aq) → 2CrCl₃(aq) + 3H₂(g)
4Cr(s) + 3O₂(g) → 2Cr₂O₃(s) (heat)
2Cr(s) + 3H₂O(g) → Cr₂O₃(s) + 3H₂(g) (steam, high temp)

Potassium dichromate (K₂Cr₂O₇): orange‑red solid, water soluble. pH sensitive equilibrium:

Cr₂O₇²⁻(orange) + H₂O ⇌ 2CrO₄²⁻(yellow) + 2H⁺

Acid → shifts left (orange), Base → shifts right (yellow).

Oxidising reactions (redox titration):
2Cr₂O₇²⁻ + 3H₂C₂O₄ + 8H⁺ → 4Cr³⁺ (green) + 6CO₂ + 7H₂O
Cr₂O₇²⁻ + 6Fe²⁺ + 14H⁺ → 2Cr³⁺ + 6Fe³⁺ + 7H₂O (orange to green)

Manganese: greyish‑white, hard, brittle. Oxidation states: +2 (MnCl₂), +4 (MnO₂), +7 (KMnO₄).

Reactions:
3Mn(s) + 2O₂(g) → Mn₃O₄(s)
Mn(s) + Cl₂(g) → MnCl₂(s)
Mn(s) + H₂SO₄(dil) → MnSO₄(aq) + H₂(g)

Potassium permanganate (KMnO₄): deep purple, strong oxidising agent. In acidic medium:
MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
In neutral/basic medium:
MnO₄⁻ + 2H₂O + 3e⁻ → MnO₂ + 4OH⁻

Titration reactions:
2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O
MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O

Iron (Fe): 4th most abundant element, essential for haemoglobin. Reacts with air (rust): 4Fe + 3O₂ → 2Fe₂O₃. With excess Cl₂: 2Fe + 3Cl₂ → 2FeCl₃.

Steel types & applications (table form):

• Carbon steel: construction, tools, machinery, pipes, tubes, automotive.
• Stainless steel (Fe + Cr, Ni): kitchen appliances, cutlery, medical equipment.
• Tool steel: cutting and drilling equipment.
• Alloy steel: fry pans, toasters, etc.

Copper (Cu): reddish‑brown, malleable, ductile, second highest electrical conductivity (after Ag).

Reactions with acids:
Cu + 2H₂SO₄(conc.) → CuSO₄ + SO₂ + 2H₂O
Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O

Metallurgy of copper: Most abundant ore chalcopyrite (CuFeS₂). Steps:

1. Concentration (froth flotation).
2. Roasting (converts FeS to FeO, removes volatile impurities).
3. Smelting in blast furnace → copper matte (Cu₂S + FeS).
4. Bessemer converter → blister copper (~98% pure).
5. Electrolytic refining: impure Cu anode, pure Cu cathode, CuSO₄/H₂SO₄ electrolyte → 99.99% pure copper.

Pakistani deposits: Saindak and Reko Diq (Balochistan) copper‑gold mines.

• Paramagnetic behaviour: due to unpaired electrons in d‑orbitals.
• Colour formation: d‑d transitions; unpaired electrons absorb visible light.
• Catalytic property: because of variable oxidation states and vacant d‑orbitals (e.g., Fe in Haber process, V₂O₅ in contact process).
• Melting point trend: increases up to middle of series (maximum unpaired electrons → strong metallic bonding) then decreases.
• Alloys: brass (Cu+Zn), bronze (Cu+Sn), stainless steel (Fe+Cr+Ni).