3.4 TRANSITION METALS

Transition metal definition

Posses partially filled d subshell as atom or stable ion

Metals in d block which are not transition metals

Zn has a full d sub shell ad Zn2+

Electronic configuration exceptions

Copper - 3d10 4s1

Chromium 3d5 4s1

How do d block attain various oxidation states

Partially filled 3d 4s orbitals similar energy

Energy to remove electrons same → multiple states

Oxidation states of chromium

Cr3+ Green

CrO42-Chromate Yellow

Cr2072- Dichromate Orange

Oxidation states of mangagnese

Mn2+ Pale pink

MnO4 - Permanganate Purple

Oxidation states of iron

Fe2+ pale green

Fe3+ brown

Oxidation states copper

Cu2+ blue

Ligand

Small molecule with lone pair can form coordinate bond to transition metal

Co ord complex

Central metal ions bonded to surround molecules ligands via coordinate bond

Coordination number

Number of ligand donor atoms

Octehedrally and tetrahedral

Octra -

6 ligands and coordinate bond 90

Tetra -

4 ligands and coordinate bonds 109.5

Octahedral solutions

[Fe(H2O)6]2+ Pale green

[Fe(H2O)6] 3+ Yellow

[Cu(H2O)6] 2+ blue

[Cr(H2O)6] 3+ dark green

[Co(H2O)6] 2+ pink

Tetrahedral solutions

[CuCl4]2- yellow green

[CoCl4] blue

Trans and cis isomer

Trans 2 Water opposite common isomer

Cis 2 water next to each other

Copper and cobalt colour change with HCl

Copper(II) pale blue → yellow green

Cobalt(II) pink → blue

Ligand exchange

Metal ligand + new ligand → New complex + Old ligand

Replacement of ligands change colour and coordination num

[Cu(H₂O)₆]²⁺ + NH₃

• Small NH3 → Cu(OH)2 ppt pale blue

• Excess NH3 → [Cu(NH₃)₄(H₂O)₂]²⁺ (deep blue)

[Co(H₂O)₆]²⁺ + concentrated HCl

Form [CoCl4]2+

Coordination number 6→ 4

Pink → blue

[Cu(H₂O)₆]²⁺ + Cl⁻ → [CuCl₄]^2-

Blue → yellow green

Colour complexes

[Cu(H₂O)₆] ²⁺ Blue

[Cu(NH₃)₄(H₂O)₂]²⁺ Deep blue

[Co(H₂O)₆]²⁺ Pink

[CuCl₄] Yellow green

[CoCl₄] Blue

Type of ligands

• H₂O ligands → octahedral, usually light colours

• NH₃ ligands → octahedral, stronger ligand → deeper colour

• Cl⁻ ligands → tetrahedral, often yellow/green/blue

Why are transition metals good catalysts

• Partial filled d orbitals allow temporary bonding with reactants

• Stablilising intermediates

Heterogenous

Catalyst different physical state (solid)

• Reactant adsorb → catalyst surface bond weaken products desorb

Homogenous

Same physical state as reactant

• Catalyst change oxidation state

• Cycle between - speed up

Nickel catalyst

Heterogenous

Hydrogenation of alkenes

Solid nickel surface gas phase H₂ + alkene

Iron catalyst

Homogenous

Haber process N₂ + H₂ → NH3

Fe surface oxidation cycle

Vanadium oxide

Heterogenous

Contact process

SO₂ → SO₃

Manganese oxide

Heterogenous

Decompostion of 2H₂O₂ → 2H₂O + O₂

Cr³⁺ and hydroxide

Small

• Grey green ppt Cr(OH)₃

Excess

• [Cr(OH)₆]^3- Green solution

Fe²⁺ and hydroxide

Small

• Fe(OH)₂ Dark green ppt

Excess

• no further reaction (brown oxidise0

Fe³⁺ and hydroxide

Small

• Fe(OH)₃

Excess

• Insoluble brown ppt

Cu²⁺ and hydroxide

Small

• Cu(OH)₂ Blue

Excess

• Insoluble blue ppt