Transition Metals

Describe how TM form ions

Lose 4s electrons before 3d electrons

Name and describe the 2 odd transition metals

Copper and Chromium

More stable with half full 4s orbital so donate a 4s electron into the 3d subshell

Define transition metal

Metal that can form one or more stable ions with an incomplete d subshell

Describe Zn and Sc

They are d block elements as their outer electron is in a d subshell

But they aren't transition metals as they don't form a stable ion with an incomplete d subshell

Describe the 4 main characteristics of TM

- Catalysts

- Variable Oxidation States

- Form complex ions

- Coloured compounds

These arise due to the incomplete d subshell

Define complex ion

central metal ion surrounded by ligands

Define ligand

molecule or ion that forms a coordinate bond with a transition metal by donating a lone pair of electrons

Define monodentate ligand

molecules or ions that can donate one electron pair to the central metal ion to form one coordinate bond

Define bidentate ligands

molecules or ions that have two atoms that each donate an electron pair to the central metal ion to form two coordinate bonds

Give examples of bidentate ligands

Define multidentate ligand

molecules or ions that have more than 2 atoms that can each donate an electron pair to the central metal ion to form more than 2 coordinate bonds

Give an example of a multidentate ligand

EDTA4-

Has 6 atoms that can each donate 1 lone pair to the central metal ion

Can form 6 coordinate bonds with a metal ion

Define coordination number

The number of coordinate bonds to the central metal atom/ ion

(NOT the same as the number of ligands)

What are the 4 main complex ion shapes?

- Octahedral

- Tetrahedral

- Square Planar

- Linear

Compare the ligands Cl- , H2O and NH3

Cl- is larger than H2O and NH3 so would have a different shape

Describe the (expected) shape complexes with H2O or NH3 ligands

Octahedral

Describe the (expected) shape complex with Cl-

Tetrahedral

Describe the reaction of Cobalt Salts with excess ammonia

[Co(H2O)6]2+ + 6NH3 ⇌ [Co(NH3)6]2+ + 6H2O

Pink ---> Light brown

Coord Num 6 ---> 6

Shape Octahedral ---> Octahedral

Describe the reaction of Copper(II) salts with excess ammonia

[Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ + 4H2O

Blue ---> Deep/ Dark Blue

Coord Num 6 ---> 6

Shape Octahedral ---> Octahedral

Describe the reaction of Cobalt salts with conc HCl

[Co(H2O)6]2+ + 4Cl- ⇌ [CoCl4]2- + 6H2O

Pink ---> Blue

Coord Num 6 ---> 4

Shape Octahedral ---> Tetrahedral

Describe the reaction of Copper Salts with conc HCl

[Cu(H2O)6]2+ + 4Cl- ---> [CuCl4]2- + 6H2O

Blue ---> Yellow/ Green

Coord Num 6 ---> 4

Shape Octahedral ---> Tetrahedral

Describe Haemoglobin

Haem group with Fe2+ complex

Coord num 4

Electrons originate from lone pair of N for Fe - N bond

Oxygen and water bind interchangeably in a reversible reaction

Carbon monoxide can substitute for oxygen so is considered toxic

What is the chelate effect?

Substitution of monodentate ligand with bidentate or multidentate ligand leads to a more stable complex

Why are transition metals ions coloured?

Due to the incomplete d subshell

How do colours of transition metals arise?

- Transition metals absorb certain frequencies of visible light

- This causes d electrons to be promoted to higher energy level

- The remaining colours of light are transmitted

Why are aqueous copper (II) ions blue in colour?

- Cu(II) ions absorb certain frequencies of visible light

- d electrons are promoted

- Blue light that remains is transmitted

Give the first equation for energy gap

∆E = hv

∆E is energy gap in joules

h is Plancks constant = 6.63 x10^-34 Js

v is frequency of light absorbed in Hz

Give the equation for v (frequency of light absorbed)

v = c / λ

v is frequency of light absorbed in Hz

c is speed of light = 3 x10^8 ms^-1

λ is wavelength of light in m (usually given as nm so convert)

Give the overall equation for Energy gap

∆E = h c / λ

What factors affect colour of transition metal complexes?

- Change in coordination number

- Change in ligand

- Change in oxidation state

No question on colorimetry

Define stereoisomers

Same structural formula but different arrangement of atoms in space

What stereoisomers can form from square planar complexes with 2 different ligands

Cis and Trans

Cis is next to each other

Trans is opposite

Describe stereoisomerism of octahedral complexes

2 different ligands 2 of one and 4 of the other

Describe optical isomers

non superimposable mirror images

Bidentate ligand optical isomers

Describe the isomerism of octahedral complexes with 2 monodentate and 2 bidentate ligands

Show Cis- Trans and Optical isomerism

Describe catalysts

- Speed up rate of reaction without being used up

- Provide an alternate reaction pathway of lower activation energy - leads to more frequent successful collisions

What is the effect of catalysts on ∆H?

No effect

Only reduces Ea

Why can transition metals act as catalysts?

Due to variable oxidation states

What are the 2 types of catalysts transition metals can act as?

- Heterogeneous

or

- Homogeneous

Define Heterogeneous catalysis

a catalyst in a different state/phase to the reactants

Why is a thin layer of metal used on a support medium for the catalyst?

- Increases SA

- Reduces costs

Give the steps involved in heterogeneous catalysis

- Adsorption (stick)

Reactant molecules adsorb onto the transition metal surface

- Chemical reaction

Bonds weaken/break - reaction takes place - new bonds form

- Desorption

Products desorb (unstick/vacate) the catalyst surface

Describe catalyst poisoning

Heterogeneous catalysts work when the reactants adsorb to the catalyst surface

Impurities in the reactants can bind to the active sites to block the reactants

We say the catalyst has been poisoned

This reduces efficiency as the surface area is reduced as active sites are blocked

The catalyst may need replacing or regenerating - poisoning can be minimised by purifying the reactants

Give the equations for the contact process

Vanadium oxide is the heterogenous catalyst

SO2 + V2O5 ---> SO3 + V2O4

V2O4 + 0.5O2 ---> V2O5

Overall: SO2 + 0.5O2 ---> SO3

Define Homogenous catalysis

Catalyst in the same state/phase as the reactants

Give the reaction between S2O8 2-(aq) and I-(aq)

without the catalyst

S2O8 2- + 2I- ---> 2SO4 2- + I2

Reaction is slow as both reactants are negative so repel

Give the reaction between S2O8 2-(aq) and I-(aq)

with the catalyst

2Fe2+ + S2O8 2- ---> 2SO4 2- + 2Fe3+

2Fe3+ + 2I- ---> I2 + 2Fe2+

Steps can occur in either order with either Fe2+ or Fe3+ being the catalyst

Define autocatalysis

the catalyst for the reaction is a reaction product

Give the reaction between MnO4- and C2O4 2-

[Manganate(VII) ions and ethanedioate ions]

2MnO4- + 5C2O4 2- + 16H+ ---> 2Mn 2+ + 8H2O + 10CO2

Both reactants are negative so reaction is initially very slow

For the reaction of MnO4- and C2O4 2-

Describe the rate of reaction of time

Initially very slow as it is uncatalysed

As Mn2+ is being formed the rate increases rapidly - catalysed

Rate decreases at the end of the reaction as reactant conc decreases

Give the mechanism for the reaction of MnO4- and C2O4 2- with the catalyst

2MnO4- + 5C2O4 2- + 16H+ ---> 2Mn 2+ + 8H2O + 10CO2

4Mn 2+ + MnO4- + 8H+ ---> 5Mn 3+ + 4H2O

2Mn 3+ + C2O4 2- ---> 2Mn 2+ + 2CO2

Mn3+ is the intermediate

Give the oxidation states, colour and ions for all the Vanadium ions

VO2 + +5 Yellow

VO²+ +4 Blue

V³+ +3 Green

V²+ +2 Violet

Describe Tollens reagent

[Ag(NH3)2]+

Aldehyde warmed with tollens reagent gives silver mirror

Aldehyde oxidised to carboxylic acid

Silver ions in tollens are reduced to solid silver

Equation for reduction of Tollens reagent

[Ag(NH3)2]+ + e- ---> Ag(s) + 2NH3

Describe redox potentials

Measure of how easily an ion or atom is to reduce to a lower oxidation state

More positive redox potential means more likely to be reduced so less stable ion

Redox potential is same as standard electrode potential under standard conditions in aqueous solution

Which complex is stronger oxidising agent and why?

[Co(H2O)6]2+

[Co(H2O)6]3+

3+ is smaller and more highly charged so gains electrons more readily

Give the half equation for Manganate ions

MnO4- + 8H+ 5e- ---> Mn2+ + 4H2O

Give the half equation ethanedioate ions?

C2O4 2- ---> 2CO2 + 2e-

How can conc of MnO4- ions be measured in its reaction with ethanedioate ions?

MnO4- ions are pink/purple colour