Transition Metals Flashcards
Where in the periodic table are transition metals found?
d-block
What are transition metals?
A metal that can form one or more stable ions with an incomplete d sub shell
Why are Scandium + Zinc not transition metals?
Does not form a stable ion with incomplete d sub shell
Sc3+ (only stable ion) has an empty d sub shell
Zn only forms Zn2+ and this has a full d sub shell
What are the Properties of Transition Metals?
- Have variable oxidation states – This is because the electrons sit in 4s and 3d energy levels which are very close, hence, electrons are gained and lost using similar amounts of energy
- Form coloured ions in solution
- Good catalysts
- Ability to form complex ions
What is a complex ion?
Metal ions surrounded by co-ordinately bonded ligand
What is a Co-ordinate bond?
A covalent bond in which both electrons in the shared pair come from same atom
What is a ligand?
Atom, ion or molecule that donates a pair of electrons to a central metal atom/ion. A ligand must have at least one lone pair of electrons
What is a monodentate ligand + Examples?
A ligand with one lone pair, H2O:, :NH3, :Cl-, :OH-, :CN-
What is a bidentate ligand?
A ligand with two lone pairs, Ethanedioate & Ethane-1,2-diamine
What is a multidentate ligand?
A ligand with more than two lone pairs, Haem & EDTA4-
How do you name complexes?
No. of Ligands
Name of ligands – if more than 1, order is A-Z
Name of metal ion (metal ion = ‘ate’ if its negatively charged complex for e.g Iron = ferrate. Copper = cuprate)
How do you calculate the Oxidation No. of Metal?
Total charge of complex – Sum of Ligand charges
What is the Co ordination Number?
No. of co ordinate bonds formed with Central Metal ion
What is the Complex shape dependent on?
Shape is dependent on the size of the ligands and the co-ordination number
Name some small ligands and how many can you fit around a central metal ion?
H2O:, :NH3 and you can fit 6 of them around a central metal ion
Name a larger ligand and how many can you fit around a central metal ion?
:Cl- and you can fit 4 around the central metal ion
Name some bidentate ligands and how many can you fit around a central metal ion?
Ethanedioate & Ethane-1,2-diamine and normally can only fit 3 around a central metal ion
What is the shape of a complex with a coordination number of 6 + Bond angles?
Octahedral – 90 degrees
What are the shapes of a complex with a coordination number of 4 + Bond angle?
Tetrahedral – 109.5 degrees – [CuCl4]2-
Square Planar – 90 degrees – Cisplatin – Pt[(NH3)2(Cl)2]
What is the shape of a complex with a coordination number of 2 + Bond angle?
Linear - 180 degrees – [Ag(NH3)2]+ a.k.a Tollens Reagent
How do you calculate Total Oxidation state of metal of complex shapes?
Total Oxidation state – Total Oxidation state of ligands
What is haemoglobin?
A protein found in the blood that helps to transport oxygen around the body
What is Haem?
A multidentate ligand found in haemoglobin
What shape is haemoglobin?
Octahedral
Explain how Haemoglobin Works?
Water is at the top initially, however, oxygen will substitute the water ligand in the lungs to form oxyhaemoglobin – transported around body. Later oxygen is given up and water takes its place
How does Carbon Monoxide poisoning work?
This is when the Carbon Monoxide ligands replace the water ligands. CO bonds strongly to Fe2+ and doesn’t get readily replaced by oxygen or water and this leads to headaches, dizziness; death if not treated as oxygen is unable to be transported
When can complex ions show optical isomers?
They can show optical isomerism when they are non superimposable mirror images
What shaped complexes with how many ligands shows optical isomers?
Octahedral complexes with 3 bidentate ligands
When can complex ions show cis-trans isomerism?
- Octahedral complexes with 4 ligands of the same type and 2 ligands of a different type
- Square planers with 2 ligands of the same type and 2 ligands of a different type
What is d orbital splitting?
This is when the d subshell split into 2 when ligands bond with the central metal ion
Explain d orbital splitting
When electrons absorb light (e.g visible), some move from ground state to the excited state (highest orbital) which creates an energy gap, ∆E
What does the frequencies absorbed depend on?
It depends on the size of ∆E. The larger the energy gap ∆E, the higher the frequency of light absorbed
What happens to those frequencies which are not absorbed?
They are reflected or transmitted
What colour is shown for those complexes with full or empty 3d subshells?
They are seen as colourless or white as no electrons can move to a higher energy level
What is the colour of complex ions dependent on?
Size of ∆E
What does the size of ∆E depend on?
- Central metal ion and oxidation state
- Type of Ligand
- Coordination number
How do you calculate the energy absorbed when electrons jump?
The formula - ∆E = hv = hc / Lambda ∆E = Energy Absorbed h = Plancks Constant (6.63 x 10-34 Js) v = frequency of light absorbed (Hz) c = speed of light (3.00 x 108 m s-1) Lambda = Wavelength of light absorbed (m)
Give an example of a ligand substitution where the co ordination number and shape remain the same (Similar sized ligands)
[Co(H2O)6]2+ + 6NH3 [Co(NH3)6]2+ + 6H2O
Colour – Pink Colour – Yellow
Shape – Octahedral Shape – Octahedral
Give an example of a ligand substitution where the coordination number and shape changes (usually when a small ligand is exchanged for a larger one)
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
Colour – Pale Blue Colour – Yellow
Shape – Octahedral Shape – Tetrahedral
Give an example of a ligand substitution where the oxidation number changes
[Fe(H2O)6]2+ [Fe(H2O)6]3+
Colour – Pale Green Colour – Yellow
Shape – Octahedral Shape – Octahedral
Give an example of a partial ligand substitution? ([Cu(H2O)6]2+ reacts with excess ammonia)
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Colour – Blue Colour – Dark Blue
Shape – Octahedral Shape – Octahedral
Give an example of a ligand substitution with different sized ligands
[Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2O
Colour – Pink Colour – Blue
Shape – Octahedral Shape – Tetrahedral
How does an increase in Entropy affect a complex?
Forms a more stable complex
Why is the enthalpy change small in ligand substitution reactions?
This is because the Bonds are broken and made have similar strengths
What happens when we substitute monodentate with bi or multidentate ligands?
Create a solution with more particles in it which means with have an increase in entropy; which also means a reaction is more likely to happen
What is the Chelate effect?
…
What is Vanadium?
A transition metal with different oxidation states and colours
What are the 4 oxidation states and colours of Vanadium?
V2+ - +2 – Violet
V3+ - +3 – Green
VO2+ - +4 – Blue
VO2+ - +5 –Yellow a.k.a Vanadate(V) ion
What type of reaction occurs when a transition metal changes oxidation state?
Redox Reaction
Explain the process by which Vanadium is reduced by zinc in an acidic solution?
2VO2+(aq) + Zn(s) + 4H+(aq) 2VO2+(aq) + Zn2+(aq) + 2H2O(l) – Yellow Blue
2VO2+(aq) + Zn(s) + 4H+(aq) 2V3+(aq) + Zn2+ (aq) + 2H2O(l) – Blue Green
2V3+(aq) + Zn(s) 2V2+ (aq) + Zn2+ - Green Violet
What do redox potentials show?
How easily an ion is reduced which is the same as electrode potentials
What type of ions are more likely to be reduced?
The least stable ions as they have the largest redox potentials
What are the standard conditions for Eꝋ values?
- Temp of 298K
- Pressure at 100kPa
- Concentrations of ions at 1 moldm-3
Explain why there may be a difference in redox potentials to the standard values in data books?
This is dependent on the environment the ion is in
What affects Redox potentials?
pH
Ligands
How can Transition Metal complexes be analysed?
This is through Colorimetry. The colours we see are compliments of the colours absorbed by the solution
What is colour dependent on?
- Type of ligand
- The shape of ligand
- Oxidation state of the central metal ion
What is a colorimeter used for?
It is used to measure the concentration of transition metal ions in solution by measuring the absorbance of light in a coloured sample.
What is a calibration curve/graph used for?
This will be plotting a graph of know concentrations to work out the concentration of an unknown solution
What are the 2 types of catalysts?
- Homogeneous
- Heterogeneous
What is a heterogeneous catalyst – Give an example?
A catalyst that is in a different state to the reactants
The Haber Process – N2(g) + 3H2(g) 2NH3(g) – A solid Iron catalyst is used.
What is a homogeneous catalyst – Give an example?
A catalyst that is in the same phase as the reactants and usually in aqueous in aqueous reactants. For example, using sulphuric acid to make an ester. Will usually form intermediate species.
What is the Contact Process?
The production of Sulfuric Acid using Vanadium(V) – V2O5 Heterogeneous catalyst
- V2O5 + SO2 V2O4 + SO3
- V2O4 + 1/2O2 V2O5
Why are Catalysts used?
They make products faster and can be used to lower the temperature required for a reaction. This saves energy and money and is better for the environment
What do impurities do?
What do impurities do?
What is Poisoning?
When an impurity blocks a site
What are the effects of catalytic poisoning?
Reduces surface area of the catalyst for the reactants and this slows down the rate of reaction
State an example of when a homogeneous catalyst is used
Oxidation of Iodide ions using peroxodisulfate (S2O82-) as a catalyst
Why is a catalyst required for this reaction (peroxodisulfate)?
The reaction is very slow and we are trying to react 2 negatively charged ions together which repel, hence, the reaction has a high activation energy
S2O82-(aq) + 2I-(aq) –> I2(aq) + 2SO42-(aq)
Explain the reaction of the Oxidation of Iodide ions using peroxodisulfate (S2O82-) as a catalyst
1) We use Fe2+ as a catalyst, we can lower the activation energy and speed up the reaction. So the first part is the reduction of peroxodisulfate
S2O82-(aq) + 2Fe2+(aq) –> 2Fe3+(aq) + 2SO42-(aq)
2) The Fe3+ intermediate produced in the first part reacts with the I- ions to produce I2 and Fe2+ is reformed
2I-(aq) + 2Fe3+(aq) –> 2Fe2+(aq) + I2(aq)
What is autocatalysis?
Another form of homogeneous catalyst where the product of the reaction catalyses for the same reaction
Give an example of autocatalysis
Reaction between C2O42- & MnO4-
Explain the reaction between C2O42- & MnO4- and why is catalyst required
The reaction is very slow as they are negative so they repel
2MnO4-(aq) + 16H+(aq) + 5C2O42-(aq) 2Mn2+(aq) + 8H2O(l) + 10CO2(g)
1) The Mn2+ catalyses the reaction converting MnO4- into Mn3+
MnO4-(aq) + 8H+(aq) + 4Mn2+(aq) 5Mn3+(aq) + 4H2O(l)
2) The Mn3+ formed reacts with the C2O42- and Mn2+ ions are reformed
2Mn3+(aq) + C2O42-(aq) 2Mn2+(Aq) + 2CO2(g)
What is the colour of V2+?
Violet
What is the colour of V3+?
Green
What is the colour of VO^2+
Blue
What is the colour of VO2^+?
Yellow
What is the colour of Cr+?
Green / violet when surrounded by 6H2O
What is the colour of CrO72-?
Orange
What is the colour of Mn2+?
Pale Pink
What is the colour of MnO4-
Purple
What is the colour of Fe2+
Pale Green
What is the colour of Fe3+
Yellow
What is the colour of Co2+
Pink
What is the colour of Ni2+
Green
What is the colour of Cu2+
Blue
What is formed when we add a transition metal to water + give 2 examples?
Metal Aqua complex – Cu[(H2O)6]2+ and Fe[(H2O)6]3+
What makes metal aqua ions acidic?
When reacting with water, H+ ions are produced to produce hydroxonium ions making it acidic
What affects the acidity of a metal aqua ion complex?
What affects the acidity of a metal aqua ion complex?
Why are 3+ ions more acidic than 2+ ions?
3+ metal ion has a higher charge density as they have a larger charge and small. This makes it more polarising than 2+ ions. They attract electrons in the O-H bond in the water more strongly which weakens the bond. Therefore, it is more likely that the H+ ions will be released which means 3+ metal ions form more acidic solutions
2+ Metal ions with Sodium carbonate reaction?
[M(H2O)6]2+(aq) + CO32- (aq) MCO3(s) + 6H2O
3+ Metal ions with Sodium carbonate reaction?
2[M(H2O)6]3+(aq) + 3CO32- (aq) 2M(OH)3(H2O)3 (s) + 3CO2 (g) + 3H2O(l)
