Transition metals

What is a d-block element?

An element where it’s highest energy electron is in the d sub-shell

What two elements have a different electron configuration?

• Cu and Cr

• 3s sub-shells are more stable when all sub-shells are fully or singly occupied

• So the 4s sub-shell is singly occupied

What is a transition element?

-A d-block element that forms at least one stable ion with a partially filled d sub-shell.

What two elements are are d-block elements but not transition elements?

• Sc and Zn as there don’t form ions with a partially filled d-sub-shell.

• In Sc3+ the d sub-shell is empty.

• In Zn2+ the d sub-shell is full.

Properties of transition elements

1. Variable oxidation states → 4s and 3d sub-shells are close in energy so it’s easy to lose electrons from either sub-level.

2. Form coloured ions

3. - Catalytic behaviour → act as an intermediate in exchange of reacting species.

- Provides surface are for reactions to occur → metal forms weak bonds with reacting species + holds then in place → Adsorption → Bonds rearranged → Products diffuse/desorb.

• TM catalysts reduce energy usage BUT can be toxic.

What are complex ions?

Transition metals bonded to one or more ligands by coordinate bonds/dative covalent bonds.

e.g. [Co(H2O)6]2+

Draw the complex ion [Co(H2O)6]2+

What is a dative/covalent bond?

A strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms, with the bonded pair of electrons donated from one atom only.

What is a ligand?

A molecule/ion that can donate a lone pair of electrons to the transition metal ion to form a coordinate bond.

Types of ligands

1. Monodentate ligands → donates one pair of electrons and forms one coordinate bond.

2. Bidentate ligands → donates 2 pairs of electrons to the TM to form 2 coordinate bonds.

3. Multidentate ligands → contains more that 2 atoms that donate pairs of electrons to form coordinate bonds.

Complex shapes:

Octahedral

• 6 coordinate bonds

• Bond angle = 90*

• e.g. [Co(H2O)6]2+

Complex shapes:

Tetrahedral

• 4 coordinate bonds

• Bond angle = 109.5*

• Occurs when ligands are large

• [CuCl4]2-

Complex shapes:

Square planar

• 4 coordinate bonds

• Bond angle = 90* in cis isomers and 180* in trans isomers

What is optical isomerism?

Give an example.

• Complexes are optical isomers when they are non-superimposable mirror images.

• Optical isomerism found in octahedral complexes with bidentate ligands.

What is cis-trans isomerism?

Give an example.

• Cis isomers have identical ligands on the same/adjacent side and trans isomers have identical ligands on opposite sides.

• Found in octahedral and square planar complexes.

• e.g. [Co(H2O)4Cl2] or cis/trans platin

What is cis platin?

• Square planar complex with 4 coordinate bonds.

• Cis platin has a bond angle of 90* and trans platin has a bond angle or 180*

• Cis platin is an anticancer drug which binds to DNA in cancer cells (Cl- bonds to N in DNA) → prevents cell division and the cell dies.

• Cis platin also prevents healthy cells from producing leading to side effects:

  1. Kidney damage

  2. Nausea/vomiting

  3. Suppressed immune system

  4. Hair loss

• trans platin doesn’t work.

What are ligand substitution reactions?

When one or more ligands are replaced with another ligand.

Ligand substitution reaction of [Cu(H2O)6]2+ with NH3

• [Cu(H2O)6]2+ (aq) + 4NH3 (aq)

  → [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)

• Pale blue solution → Dark blue solution

Ligand substitution reaction of [Cu(H2O)6]2+ with Cl-

• [Cu(H2O)6]2+ (aq) + 4Cl- (aq) → [CuCl4]2- (aq) + 6H2O (l)

Pale blue solution → yellow solution (green if it is at equilibrium)

Ligand substitution reaction of [Co(H2O)6]2+ with Cl-

• [Co(H2O)6]2+ (aq) + 4Cl- (aq) → [CoCl4]2- (aq) + 6H2O (l)

• Pink solution → blue solution

Ligand substitution of [Cr(H2O)6]3+ with NH3

• [Cr(H2O)6]3+ (aq) + 6NH3 (aq) → [Cr(NH3)6]3+ (aq) + 6H2O (l)

• Pale purple solution (can be green to start with due to impurities) → purple solution

• → turns green when heated.

How does haemoglobin work?

• Causes blood to appear red

• Carries oxygen from the lungs to cells in the body

• Contains and Fe2+ ion which binds to oxygen and carries it around the body to muscles

• Oxygen binds reversibly and forms a coordinate bond

• O2 and CO2 exchange via ligand substitution

• CO forms stronger coordinate bonds than O2 and bind irreversibly

Precipitation reactions; NaOH reactions

• Reaction with Cu2+

• Cu2+ (aq) + 2OH- (aq) → Cu(OH)2 (s)

• Pale blue solution → pale blue ppt

• Insoluble in excess NaOH

Precipitation reactions: NaOH reactions

• Reaction with Cr3+

• Cr3+ (aq) + 3OH- (aq) → Cr(OH)3 (s)

• Pale purple solution → Dark green ppt

• Is soluble in excess NaOH:

• Cr(OH)3 (s) + 3OH- → [Cr(OH)6]3- (aq) → produces a dark green solution

Precipitation reactions: Reactions with NaOH

• Reaction with Mn2+

• Mn2+ (aq) + 2OH- (aq) → Mn(OH)2 (s)

• Pale pink solution → Pale brown ppt (can darken on standing due to oxidation)

• Insoluble in excess NaOH

Precipitation reactions: Reactions with NaOH

• Reaction with Fe2+

• Fe2+ (aq) + 2OH- → Fe(OH)2 (s)

• Pale green solution → Dark green ppt (can darken on standing due to oxidation from Fe2+ to Fe3+)

• Insoluble in excess NaOH

Precipitation reactions: Reactions with NaOH

• Reaction with Fe3+

• Fe3+ (aq) + 3OH- (aq) → Fe(OH)3 (s)

• Pale yellow solution → orange/brown precipitate

• Insoluble in excess NaOH

Precipitation reactions: Reactions with NH3

• Reaction with [Cu(H2O)6]2+

(REPEAT)

• [Cu(H2O)6]2+ (aq) + 2NH3 (aq) → [Cu(OH)2(H2O)4] (s) + 2NH4+

• (NH3 is added drop wise)

• Pale blue solution → Pale blue ppt

• Soluble in excess NH3 (aq):

• [Cu(OH)2(H2O)4] (s) + 4NH3 (aq) → [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O (l) + 2OH- (dark blue solution)

• >Ligand substitution

Precipitation reactions: Reactions with NH3

• Reaction with [Cr(H2O)6]3+

• [Cr(H2O)6]3+ (aq) + 3NH3 (aq) (dropwise) → [Cr(OH)3(H3O)3] (s) + 3NH4+ (aq)

• Pale purple solution → Dark green solution

• Soluble in excess HN3 (aq):

• [Cr(OH)3(H20)3] (s) + 6NH3 (aq) —> [Cr(NH3)6]3+ (aq) + 3H2O (l) + 3OH- (aq) (purple solution)

Precipitation reactions: Reactions with NH3

• Reaction with [Mn(H2O)6]2+

• [Mn(H2O)6]2+ (aq) + 2NH3 (aq) → [Mn(OH)2(H20)4] (s) + NH4+ (aq)

• Pale pink solution → Brown ppt

• Insoluble in excess NH3 (aq)

Precipitation reactions: Reactions with NH3

• Reaction with [Fe(H2O)6]2+

• [Fe(H2O)6]2+ (aq) + 2NH3 (aq) →

  [Fe(OH)2(H2O)4] (s) + 2NH3+ (aq)

• Pale green solution → Dark green precipitate

• Insoluble in excess NH3 (aq)

Precipitation reactions: Reactions with NH3

• [Fe(H20)6]3+ (aq)

• [Fe(H2O)6]3+ (aq) + 3NH3 (aq) → [Fe(OH)3(H2O)] (s) + 3NH4+ (aq)

• Pale yellow solution → orange/brown ppt

• Insoluble in excess NH3 (aq)

Redox reactions:

• Oxidation of Fe2+ → Fe3+

• Fe2+ can be oxidised with H+/MnO4-

• MnO4- (aq) + 8H+ (aq) + 5Fe2+ (aq) → Mn2+ (aq) + 5Fe3+ (aq) + 4H2O(l)

• Purple solution → Pale pink solution

• Mn is reduced since the oxidation number reduces from +7 in MnO4- to +2 in Mn2+ (Oxidising agent)

• Fe is oxidised since the oxidation number increases from +2 in Fe2+ to +3 in Fe3+

Redox reactions:

• Reduction of Fe3+ → Fe2+

• 2Fe3+ (aq) + 2I- (aq) → 2Fe2+ (aq) + I2 (aq/s)

• Orange/brown solution → green solution + dark brown solution (dominates)

• In the presence of I-, Fe3+ can reduces to Fe2+

• The overriding colour change is rusty brown → dark brown

Redox reactions:

• Oxidation of Cr3+

• Cr3+ can be oxidised with H2O2/OH-

• Step 1: 2Cr3+ (aq) + 3H2O (l) +10OH- (aq) → 2CrO42- (aq) +8H2O (l)

• Green solution → Yellow solution

• Use hot alkaline H2O2

• Step 2: 2CrO42- +2H+ → Cr2O72- +H2O

• Yellow → Orange

Redox reactions:

• Reduction of Cr2O72- to Cr3+

• Treat Cr2O72- with zinc (reducing agent)and either HCl or H2SO4

• Cr2O72- (aq) +14H+ (aq) + 3Zn (s) → 2Cr3+ (aq) + 3Zn2+ (aq) + 7H20 (l)

• Orange → Green (2Cr3+)

Redox reactions:

• Reduction of copper (II)

• 2CU2+ (aq) + 4I- → 2CuI (s) + I2 (aq)

• Blue solution → white ppt + brown solution (offwhite)

Redox reactions:

• Disproportion of Cu+

• Disproportion occurs readily in solution

• 2Cu+ (aq) → Cu (s) + Cu2+ (aq)

• Colourless solution → brown ppt + blue solution