Transition Metal

Define a d block element

An element that has a d orbital as its highest energy occupied orbital

Define a transition metal

An element that has a d orbital as its highest energy occupied orbital that has at least one ion with an incomplete d-sub shell

Why does chromium have the electronic configuration of [Ar] 3d^5 4s^1 instead of [Ar] 3d^4 4s² and coppor have [Ar] 3d^10 4s^1 instead of [Ar] 3d^9 4s²

Molecules are more stable in subshells are full or half full

Define a ligand

Species capable of donating a lone pair of electrons and forming a coordinate dative bond to a central metal ion

Define coordinate (dative) bond

Both electrons of shared pair come from the same atom

Define complex ion

Central metal ion attached to one or more ligand

Define coordination number

The number of coordinate bonds formed by a central metal ion

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

Give the bond angle, coordination number and shape

90 degrees, octahedral, 6 coordination

Draw the complex ion Pt(NH3)2Cl2

(Square planar)

Give the bond angle and coordination number

Pt has a charge of 2+

90 degrees, coordination of 4

Draw the complex ion [CoCl4]2-

(Tetrahedral)

Give the bond angle and coordination number

109.5 Tetrahedral, 4 coordination

Draw the complex ion [Ag(NH3)2]+

Give the bond angle, coordination number and shape

Linear, 180, coordination 2

What is a ligand substitution reaction

One ligand is replaced by another (often with a colour change)

Define didentate ligands and give an example

Donate 2 lone pairs of electrons to a metal ion

Form 2 coordinate binds with a central metal ion each

Example - C2O4²-

Define a hexadentate ligand

Donates 6 lone pairs of electrons to a metal ion

Forms 6 coordinate bonds with central metal ion

What are the properties of transition metals (oxidation states, in solutions)

• Have variable oxidation states because the electrons that sit in 4s and 3d have very close energy levels so electrons are gained and lost using a similar amount of energy

• Form coloured ions in solution

• Form complex ions

What is the colour of Fe²⁺ and Fe³⁺ ions in solution

Fe²⁺ - Light green

Fe³⁺ - Orange

What is the colour of Cu⁺ and Cu² in solutions

Cu⁺ - Colourless

Cu²⁺ - Blue

What happens to Cu⁺ ions in solution and why

• Cu⁺ has a full 3d subshell so forms colourless compounds.

• It is unstable and disproportionates in solutions

Cu₂O_(s) + H₂SO_4(aq) → Cu_(s) + CuSO_4(aq) + H₂O

Cu₂O_(s) (+1)

Cu_(s) (0) Brown solid

CuSO_4(aq) (+2) Blue sol.

Give examples of small ligands (can fit 6 around a central metal ion)

• H₂O

• NH₃

• CN^-

How many Cl^- ligands can fit around one central metal ion

4

Why are transition metals coloured and why do different complexes have different colours

• 3d orbital energy levels are split by ligands

• Absorption of energy in visible light causes electrons to move to higher energy levels

• Frequency absorbed is linked to the energy gap between the d energy levels by E=hv

• Size of energy gap is affected by the ligands, the central metal ion and its oxidation state

• Colour seen is that of wavelengths transmitted not absorbed - complementary colour

• Different complexes have different colours due to different number of d electrons and different splitting of the d orbitals. These lead to different wavelengths being absorbed and different complementary colours being seen

How can transition metals act as heterogenous catalysts

• Available 3d and 4s electrons are used to form weak bonds with reactant molecules, so reactants adsorb on to the solid metal surface

• Bonds within reactants weaken allowing a faster reaction as activation energy is lowered

• Weak dative bonds break and products desorb off catalyst surface

How can transition metals act as homogenous catalysts

• Variable oxidation states of transition metal allow an alternative route with a lower activation energy

• Ions can act as oxidising and reducing agents in the reaction, being regenerated

Show the equations and expected colour changes from the reaction of Fe²⁺ and Fe³⁺ with alkali (NaOH or NH3)

Fe²⁺_(aq) + 2OH^-_(aq) → Fe(OH)_2(s)

Pale green sol → Green ppt

Fe³⁺_(aq) + 3OH^-_(aq) → Fe(OH)_3(s)

Orang sol → Brown ppt

How can the amount of Fe³⁺ be quantified

First reduce Fe3+ to Fe2+ with Zn / H2SO4. ​

Filter to remove excess Zn​

Titrate resulting Fe2+ using acidified potassium mangantate (VII)

Write the equation and expected colour change for the reaction of Cu²⁺ with NaOH

Cu²⁺ (aq) + 2OH (aq) → Cu(OH)₂ (s) (Precipitation)​

Blue sol → Blue ppt

Cu²⁺ forms a blue complex in water. Write the equation and expected colour change for the reaction of the Cu²⁺ complex with excess ammonia

[Cu(H₂O)₆]²⁺_(aq) → Cu(OH)_2(s) → [Cu(NH₃)₄(H₂O)]²⁺ (Precipitation + ligand sub.)

Blue sol → Blue ppt → Deep blue sol.

Overall - [Cu(H₂O)₆]²⁺_(aq) + 4NH_3(aq) ⇌ [Cu(NH₃)₄(H₂O)₂]²⁺_(aq) + 4H₂O_(l)

Blue sol → Deep blue sol.​

How can you determine the percentage of Copper in brass

• Oxidise a known mass of brass using a strong oxidising agent e.g. conc HNO₃

• All metals present will be oxidised to form metal nitrates

• Neutralise with excess Na₂CO₃

• Add excess potassium iodine solution

• 2Cu^2+_(aq) + 4I^-_(aq) → CuI_(s) + I_2(aq)

• Titrate the I₂ produced sodium thiosulphate solution of known concentration

• Add starch indicator near end point (

Explain how a calibration curve can be constructed and used to find an unknown concentration

• Dilute solution X by known amounts to produce a series of solutions of known concentration

• Choose filter of the complementary colour to the solution

• Zero the colorimeter using the same solvent in the cuvette

• Measure absorbance of different solutions

• Plot a graph of absorbance (y) against concentration (x)

• Add a line of best fit

• Measure absorbance of unknown concentration

• Use the calibration curve and absorbance to find the concentration

Write the equation and expected colour change for the reaction of the Cu(OH)₂ with excess ammonia

Cu(OH)_2(s) + 2H₂O_(l) + 4NH_3(aq) → [Cu(NH₃)₄(H₂O)₂]²⁺_(aq) + 2OH^-_(aq)