Chapter 4 - d and f Block Elements

Imagine periodic table like apartment building. s-block on left balcony, p-block right balcony, middle block is d-block ground floor busy market 3 to 12 groups 4 periods 4th to 7th.

Transition elements are d-block elements whose atoms or ions have partially filled d-orbitals. Zinc Zn has full d10 not considered transition by IUPAC strict definition because Zn2+ also full. Scandium Sc empty after losing 3 electrons also not. But for exam all d-block often called transition for simplicity.

General outer configuration (n-1)d1-10 ns1-2. Last electron goes to d not s. So properties different hard metals high melting shiny.

Configuration shows exceptions due to extra stability half filled and fully filled. Chromium Cr atomic number 24 expected [Ar] 3d4 4s2 but actual 3d5 4s1 half filled extra stable. Copper Cu 29 expected 3d9 4s2 actual 3d10 4s1 fully filled stable. Similarly Mo, Ag, Au show same.

Properties: all metals hard except Zn Hg soft, high melting point due to strong metallic bonding plus covalent from d electrons tungsten W highest melting 3422 C filament bulb. High density, high enthalpy atomization.

Daily: tungsten filament bulb glows high melting, copper wires conductivity, iron hammer hard metal, gold jewellery not reactive.

Atomic radius across period 3d decreases slightly from Sc to Ni then slight increase to Zn because nuclear charge pulls in but poor shielding d electrons little increase, down group increases due to new shell.

Ionization enthalpy: first IE increases across but irregular due to stable config, second third high. Generally high compared to s-block due to small size.

Melting point trend increases to Cr Mo W middle due to more unpaired d electrons strong bonding then decreases to Zn as pairing reduces bonding. So middle elements hardest high melting Cr Mo W, Zn low melting soft.

Daily: cutting tools made of tungsten carbide hardest high melting, mercury Hg liquid low melting weak bonding.

Transition metals show many oxidation states because ns and (n-1)d both can lose. Example manganese Mn +2 to +7 range widest +2 MnSO4 pale pink +4 MnO2 brown +7 KMnO4 purple. Iron +2 green +3 yellow brown, chromium +3 green +6 orange yellow.

Colour due to d-d transitions electrons jump between split d-orbitals in presence of ligands water ammonia absorbs visible light complement colour seen. For d0 like Ti4+ white TiO2 paint no d electron no transition, d10 Zn2+ white also no transition, but charge transfer gives colour like KMnO4 purple d0 but O to Mn charge transfer, K2Cr2O7 orange also charge transfer.

Daily: blue CuSO4 copper sulphate blue due to d9 absorbs orange, white TiO2 used in white paint sunscreen, purple KMnO4 antiseptic, orange dichromate lab oxidizing.

Magnetic: if unpaired electrons present paramagnetic attracted to magnet like iron filings attracted, more unpaired stronger. Example Mn2+ d5 5 unpaired strongest paramagnetic, Ti2+ less. If all paired diamagnetic weakly repelled like Zn2+ d10 no unpaired, TiO2 white diamagnetic.

Ferromagnetic special strong permanent magnet Fe Co Ni domains aligned permanent magnet.

Catalytic: transition metals good catalysts because variable oxidation states can give take electrons, and provide surface for reactants to adsorb. Examples: Fe in Haber ammonia N2+3H2 2NH3, V2O5 in Contact H2SO4 2SO2+O2 2SO3, Ni in hydrogenation vegetable oil to ghee, Pt in catalytic converter car converts CO to CO2, Ziegler Natta TiCl4 + Al trialkyl for polyethylene plastic.

Potassium dichromate K2Cr2O7 orange prepared from chromite ore FeCr2O4 steps: roast with Na2CO3 air gives Na2CrO4 yellow, acidify gives Na2Cr2O7, add KCl gives K2Cr2O7 orange. Strong oxidizing agent acidic: Cr2O7 2- +14H+ +6e- ->2Cr3+ +7H2O orange to green Cr3+ used in titration, oxidizes Fe2+ to Fe3+, I- to I2, H2S to S. Equilibrium with chromate yellow: 2CrO4 2- yellow +2H+ <-> Cr2O7 2- orange +H2O pH dependent acidic orange basic yellow.

Potassium permanganate KMnO4 purple prepared from pyrolusite MnO2 fuse with KOH KNO3 gives K2MnO4 green manganate, acid or Cl2 gives KMnO4 purple. Strong oxidizer: acidic MnO4- +8H+ +5e- -> Mn2+ colourless +4H2O purple to colourless used titration, oxidizes Fe2+ to Fe3+ oxalate to CO2. Alkaline neutral to MnO2 brown precipitate. Neutral KMnO4 antiseptic wound cleaning.

Daily: KMnO4 purple crystals water purification antiseptic, K2Cr2O7 lab oxidizing leather tanning.

f-block last electron goes to f orbital deep inside. Two series: lanthanoids 4f Ce 58 to Lu 71 14 elements, actinoids 5f Th 90 to Lr 103 14 elements placed separately below periodic table.

Lanthanoid contraction: radius decreases steadily Ce to Lu atomic and ionic because poor shielding by 4f electrons each added proton pulls electrons closer effective nuclear charge increases radius shrinks. Consequences: Zr and Hf almost same size similar properties difficult to separate, basicity decreases across.

Actinoid contraction similar 5f poor shielding Th to Lr radius decreases. Actinoids more radioactive and complex chemistry many oxidation states like U +3 to +6.

Daily: lanthanoids phosphors TV screen colour, magnets Nd strong magnets, actinoids uranium nuclear fuel power plants.

Transition metals daily everywhere: stainless steel iron + Cr Ni kitchen utensils rust proof Cr forms oxide layer, titanium Ti implants joints light strong corrosion resistant, copper wires electricity best conductor after Ag, nichrome Ni Cr heating coil heater toaster, alloys brass Cu Zn musical instruments, bronze Cu Sn statues, gold jewellery Au not reactive shiny, platinum Pt jewellery catalyst car.

Battery: Ni-Cd rechargeable, Li-ion uses Co oxides.

f-block: cerium in petrol lighter flint, lanthanum in camera lens, neodymium NdFeB strongest magnets earphones motors, uranium U-235 nuclear fuel power plant electricity, thorium future fuel.