(1) Transition Metals Flashcards
Define a Transition Element
An element which forms at least one stable ion with a partially filled d sub-shell.
What are the key features of Transition Elements?
- Form complex ions
- Coloured ions
- Catalytic properties
- Variable oxidation states
How is the electron configuration of a Transition Metal ion determined?
FIRST IN - FIRST OUT
Electrons fill up 4s subshell before 3d so electrons are also removed from 4s subshell before 3d.
e.g.
V = 1s2 2s2 2p6 3s2 3p6 4s2 3d3
V+ = 1s2 2s2 2p6 3s2 3p6 4s1 3d3
V2+ = 1s2 2s2 2p6 3s2 3p6 3d3
Define a Coordinate Bond.
A shared pair of electrons which have both come from the same atom.
Define a Ligand.
Forms a Dative Bond with a Transition Metal Ion.
Define Coordination Number.
Number of Coordinate Bonds formed with Transition Metal.
Define a Complex Ion.
Transition Metal Ion surrounded by Ligands.
Define a Monodentate Ligand.
Has 1 lone pair and forms a Dative Bond with Transition Metal Ion.
Define a Bidentate Ligand.
Has 2 lone pairs and forms 2 Dative Bonds with Transition Metal Ion.
Define a Multidentate Ligand.
Has 2 or more lone pairs and forms 2 or more Dative Bonds with Transition Metal Ion.
Which complexes usually form a Linear Shape?
Ag+ complexes
e.g.
[Ag(NH3)2]+
Which complexes form a Tetrahedral shape?
Large Ligands
e.g. Cl-
Which complexes form a Square Planar shape?
Pt2+ complex
e.g.
[PtCl4]2-
Which complexes form a Octahedral shape?
Most complexes
e.g.
[Cu(H2O)6]2+
Give an example of a Hexadentate Ligand.
EDTA4-
EDTA can form 6 Coordinate Bonds as it has 6 lone pairs.
2x on N, 4x on O
What (observable) changes are made when:
[Cu(H2O)6]2+ + 4Cl- –> [CuCl4]2- + 6H2O
Blue Solution –> Yellow Solution
Octahedral –> Tetrahedral
(Coordination Number) 6 –> 4
What happens to the feasibility of a reaction when 6 Monodentate Ligands are replaced by 3 Bidentate Ligands?
FEASIBILITY INCREASES
Large increase in entropy (4 moles of reactants becomes 7 moles of products)
(CHELATE EFFECT)
Explain why this reaction is feasible.
[Cu(NH3)6]2+ + 3H2NCH2CH2NH2 [Cu(H2NCH2CH2NH2)3]2+ + 6NH3
The enthalpy change is zero.
Because the same number of Cu-N bonds are broken and formed.
There are 7 molecules produced from 4 molecules,
So there is a large increase in entropy.
The ∆G value will be negative.
What is an example of a Transition Metal Complex found in the blood?
HAEMOGLOBIN
(6 Coordinate Bonds)
- 4 from N to Fe2+ (haem)
- 1 from O2 to Fe2+
- 1 from globin to Fe2+
Why is Carbon Monoxide (CO) toxic?
CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin.
This prevents O2 from bonding to the Fe2+, causing suffocation.
Define Stereoisomerism. What is the form of Stereoisomerism sometimes displayed by Ligands?
Same Structural Formula, atoms occupy different positions in space. Cis-Trans Isomerism.
What is a Cis Isomer?
Alike Ligands are next to each other.
What is a Trans Isomer?
Alike Ligands are opposite one another.
What is Cisplatin?
A Cancer Drug.
Binds to DNA, preventing DNA replication.
The 2 Cl- ions are substituted for 2 N atoms on adjacent Guanine bases.
How can damage to healthy cells be minimized when using Cisplatin?
- Target cancerous cells.
- Low dosage
What is Optical Isomerism? When does it occur?
A form of stereoisomerism where the complex forms non-superimposable mirror images of itself.
This only occurs when complexes form with at least two bidentate ligands.
How can Optical Isomers be distinguished?
- Shine plane polarised light at the mixture
- Isomers rotate light in opposite directions
How can the colours of light be remembered?
ROY G BIV
Which colours of light are low in energy?
ROY
- Red
- Orange
- Yellow
Which colours of light are high in energy?
BIV
- Blue
- Indigo
- Violet
Why are Transition Metal compounds coloured?
- Partially filled d-subshell
- Certain colours (energies) of light are absorbed while the others are transmitted/reflected
- d-subshell electrons absory energy matching the difference between the ground and excited state
- Electrons are excited
Is light transmitted or reflected from a solution?
Transmitted.
What does a TM compound need to absorb light?
A partially filled d-subshell.
What causes a TM compound to appear Red/Orange?
If a transition metal compound has LARGE ∆E between d sub-shells:
⦁ High energy light (i.e. Violet, Indigo and Blue)
⦁ will be absorbed to excite the electrons
⦁ Red, Orange, Yellow light will be reflected
⦁ This means the compound will look Red/Orange
What causes a TM compound to appear Blue/Purple?
If a transition metal compound has SMALL ∆E between d sub-shells:
⦁ Low energy light (i.e. Red, Yellow and Orange)
⦁ will be absorbed to excite the electrons
⦁ Blue, Indigo, Violet light will be reflected
⦁ This means the compound will look Blue/Purple
What can affect the colour of a TM compound?
∆E between d-orbitals can be altered by a:
- Change in ligands
- Change in metal oxidation state
- Change in complex’s coordination number
- Change in complex’s shape
How is ∆E calculated? (equation)
∆E = hc/λ
- ∆E is change in energy
- h is Planck Constant (6.626 x 10-34 J·s)
- c is speed of light (3 x 108 m/s)
- λ is wavelength of light
How can the concentration of a TM solution be determinded using Colorimetry?
- An appropriate ligand (such as -SCN) is added to the solution in order to intensify the colour.
- A range of solutions of the same complex ion are made of known concentrations.
- One at a time these are tested in a colorimeter and the transmission (or absorbance) is measured.
- A graph is plotted of Conc vs Transmission (or absorbance) and a line of best fit drawn.
- The transmittance/absorbance of the unknown solution is measured in a colorimeter, and its concentration is determined by reading off the calibration curve.
What should be done before taking a reading during Colorimetry? Why?
Place a cuvette filled with water (solvent) into the colorimeter and set to zero
(Reason) Negates/removes absorbance due to solvent and ensures accuracy
What are other key experimental points of Colorimetry?
- Length of solution’s container affects the amount of absorption as distance light travels is affected.
- A filter is used to only allow one colour through the sample (use opposite light to colour of solution so light is strongly absorbed by sample)
What is a Heterogenous Catalyst?
Catalyst and Reactants are in different phases.
What is a Homogenous Catalyst?
Catalyst and Reactants are in the same phase.
Outline Heterogenous Catalysis.
- Reactants adsorb onto catalyst surface (active site of catalyst)
- Reactant bonds break then product bonds form
- Product’s molecules desorb from catalyst’s surface
How are catalysts made more efficient?
INCREASE SURFACE AREA
- by using a fine powder
- by using honeycomb design/support then spread catalyst on it
Why don’t catalysts last forever?
Poisoning can occur. Poison strongly adsorbs to catalyst’s active site and blocks it, reactant can’t displace it.
How can the Haber Process by poisoned?
Sulphur impurities can be present in CH4 that generates H2 gas, poisoning Fe catalyst.
Outline the Haber Process.
N2(g) + 3N2(g) 2NH3(g
Outline the Contact Process.
Catalysed by solid Vanadium (V) Oxide (V2O5)
STEP 1:
Sulfur Dioxide is oxidised to Sulfur Trioxide.
SO2(g) + V2O5(s) –> SO3(g) + V2O4(s)
STEP 2:
The Vanadium (IV) Oxide is then converted back to Vanadium (V) Oxide with oxygen.
2V2O4(s) + O2(g) –> 2V2O5(s)
OVERALL REACTION:
2SO2(g) + O2(g) –>2SO3(g)
Sulfuric Acid is then formed by reacting SO3 with H2O
Outline how Methanol is manufactured.
Firstly this reaction forms a mixture known as synthesis gas
CH4(g) + H2O(g) –> CO(g) + 3H2(g)
Then the following reaction is catalysed by solid Chromium (III) Oxide – Cr2O3
CO(g) + 2H2(g) –> CH3OH(g)
What is Autocatalysis?
One of the products of the reaction actually catalyses the reaction as it proceeds further.
Outline the overall equation of oxidation of Ethanedioic Acid by Manganate (VII) Ions, and name the Autocatalyst.
2MnO4-(aq) + 16H+(aq) + 5C2O42-(aq) –> 2Mn2+(aq) + 8H2O(l) + 10CO2(g)
Mn2+(aq) acts as the autocatalyst.
How does rate of reaction change during Autocatalysis?
Initially the rate is slow (usually due to repulsion between negative ions), but as more Catalyst is produced the rate increases (name the catalyst).
What is the first step of Autocatalysis (ethanedioic acid and manganate ions)?
4Mn2+(aq) + MnO4-(aq) + 8H+(aq) –> 5Mn3+(aq) + 4H2O(l)
In the first step the Mn2+ is oxidised to MnO4-.
What is the second step of Autocatalysis (ethanedioic acid and manganate ions)?
2Mn3+(aq) + C2O42-(aq) –> 2CO2(g) + 2Mn2+(aq)
In the second step the Mn3+ is reduced by C2O42-
Is Autocatalysis an example of Heterogenous Catalysis or Homogenous Catalysis?
Homogenous Catalysis.
Why can’t Group 1 Metals act as Catalysts?
They only have 1 oxidation state.
Why does this reaction have a high Ea?
S2O82-(aq) + 2I-(aq) –> 2SO42-(aq) + I2(aq)
The 2 negative ions repel each other.
Give an example of Homogenous Catalysis (reaction). Outline both steps.
S2O82-(aq) + 2I-(aq) –> 2SO42-(aq) + I2(aq)
STEP 1: S2O82-(aq) + 2Fe2+(aq) –> 2SO42-(aq) + 2Fe3+(aq)
STEP 2: 2I-(aq) + 2Fe3+(aq) –> I2(aq) + 2Fe2+(aq)
CATALYST: Fe2+
How does colour change in this equation?:
Fe2+ –> Fe3+
Green to Brown.
How does colour change in this equation?
MnO4- –> Mn2+
Purple to Colourless.
How does colour change in this equation?
Cr2O72- –> Cr3+
Orange to Green
