Transition Metals Flashcards
Define transition metal
A transition metal is one that forms at least one stable ion with a partially filled d subshell.
Which two elements are part of the d block but not considered transition metals?
Zinc and Scandium
Give the charge, electron configuration and reason as to why Scandium is not a transition metal.
Sc3+
[Ar] 4s0 3d0
Sc3+ is the only ion. The d subshell is empty.
Give the charge, electron configuration and reason as to why Zinc is not a transition metal.
Zn2+
[Ar] 4s0 3d10
Zn2+ is the only ion. The d subshell is full.
What are the two exceptions when writing electron configuration of transition metals?
Chromium (4s1 3d10)
Copper (4s1 3d10)
How are electrons lost from a transition metal?
First in, first out. So 4s are lost before 3d
4 features of transition metals
- Form complex ions
- Coloured ions
- Catalytic properties
- Variable oxidation states
Define coordinate bond.
A covalent bond is formed when both electrons are donated from the same atom.
Define ligand
A molecule/ion with a lone pair can form a coordinate bond with a metal ion.
Define coordination number
Number of coordinate bonds with the central metal ion
Define complex ion
Central metal ion surrounded by ligands
Monodentate ligand
Each ligand forms one coordinate bond
Bidentate ligand
Each ligand forms 2 coordinate bonds
Examples of monodentate ligands
H2O-:
Cl-:
:-NH3
:-CN
Examples of bidentate ligands
Ethane-1,2-diamine, or 1,2-diaminoethane (NH2CH2CH2NH2)
Ethanedioate ion (C2O4 2-)
Common shapes which transition metal complexes form
Octahedral
Square planar
Tetrahedral
Linear
What shape do complexes forming 6 coordinate bonds occupy? Give an example
Octahedral
Copper (II) Hexa Aqua Ion ([Cu(H2O)6]2+)
What shapes do complexes forming 4 coordinate bonds occupy? Give examples
- Tetrahedral
Cobalt (II) Chloride Ion ([CoCl4]2-) - Square Planar
Nickel (II) Tetra Cyano Ion ([Ni(CN)4]2-)
What shape do complexes forming 2 coordinate bonds occupy? Give an example and its use.
Linear
Silver (I) Ammonia Ion ([Ag(NH3)2]+)
The active part of Tollens’ reagent used to distinguish between aldehydes and ketones
Example of a hexadentate ligand
EDTA 4-
Occupies octahedral shape
Two coordinate bonds from N atoms and four coordinate bonds from the O- ions
Why do chloro complexes tend to be tetrahedral?
The chloride ligand is too big to fit any more than 4 Cl- ligands around the metal ion
Show how the complex [Cu(H2O)6]2+ can be converted into [Cu(H2O)2(NH3)4]2+ and state the colour of the new complex
[Cu(H2O)6]2+ + 4NH3 <—-> [Cu(H2O)2(NH3)4]2+ + 4H2O
DEEP BLUE
When does the chelate effect occur?
When a monodentate ligand is substituted by a bidentate or multidentate ligand
An example of the chelate effect
[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 <–> [Cu(H2NCH2CH2NH2)3]2+ + 6H2O
6 monodentate H2O ligands are replaced by 3 bidentate ethane-1,2-diamine ligands.
4 molecules on left turn into 7 molecules on right
Large increase in entropy
Thermodynamically very favourab;e
Entropy (ΔS) is positive.
EXAM STYLE QUESTION:
Explain why this reaction is feasible:
[Cu(NH3)6]2+ + 3H2NCH2CH2NH2 <–> [Cu(H2NCH2CH2NH2)3]2+ + 6NH3
- Enthalpy change approximately zero
= same number of Cu-N bonds broken and formed - Large increase in entropy, positive entropy
= 7 molecules produced from 4 molecules - Therefore, ΔG= negative
Bonding in haemoglobin
Made of central Fe2+ ion, forms 4 bonds to ring system called porphyrin.
- Bond in square planar arrangement- 4 coordinate bonds between Fe2+ and N atoms in haem structure.
- 1 coordinate bond between Fe2+ and globin protein.
- 1 coordinate bond between Fe2+ and O2 molecules.
What happens when O2 molecule has been transported around the body to where it is needed?
Coordinate bond breaks releasing O2
CO2 can bond in its place to be transported to lungs
Why is 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.
Steroisomer definition
Have same structural formula but different arrangement of atoms in space.
Two types of stereoisomerism
Geometrical isomerism- Cis-trans isomerism
Optical isomerism- non-superimposable mirror images
Example of octahedral complex with cis-trans isomerism
[CoCl2(NH3)4]+
Example of square planar complex with cis-trans isomerism
[PtCl2(NH3)2]
What is the cis isomer of [PtCl2(NH3)2] known as and what is it effective for?
Known as cisplatin
Effective anti-cancer drug
How does cisplatin work to prevent DNA replication?
Cisplatin binds to DNA in cancer cells and stops cell replication. The 2 Cl- ions on Cisplatin are substituted for 2 N atoms on adjacent guanine bases.
Example of cis-trans isomerism with bidentate ligand
[Cr(H2O)2(C2O4)2]-
When does optical isomerism occur in complexes?
Complexes form with at least 2 bidentate ligands and 2 monodentate ligands
Structure has to be cis.
What is optical isomerism
A form of stereoisomerism where the complex forms non-superimposable mirror images of itself.
What is the only method of finding which isomer is present?
Using the fact that optical isomers rotate a plane of polarised light in opposite directions.
Examples of optical isomer complexes
[Ni(H2NCH2CH2NH2)3]2+
[Co(H2O)2(C2O4)2)
Why are transition metals coloured?
All have partially filled d subshells
All d orbitals are of equal energy= ground state
Presence of other atoms causes d orbitals to have change in energy
Enables e- to be excited from one d orbital to another.
Energy needed for transition taken from visible light
Colour of light absorbed missing from the light that reflects from substance.
Colour seen is reflected/transmitted.
Diff in energy between d subshells= ΔE
ROY
Low energy
BIV
High energy
If a transition metal has small ΔE…
- Low energy light (ROY) absorbed to excite e-
- BIV reflected
- Compound looks blue/purple
If a transition metal has a big ΔE…
- High energy light (BIV) absorbed to excite e-
- ROY reflected
- Compound looks red/orange
What changes alter the colour of a compound
Change in LIGANDS
Change in OXIDATION STATE of metal
Change in COORDINATION NUMBER of complex
Change in SHAPE of complex
Method to find concentration of unknown sample from callibration curve
- Measure the absorbance of known concentrations
- Plot graph of absorbance v. concentration
- Read value of concentration from measured absorbance of unknown from graph.
Catalyst definition
Substance that increases ROR without being used up itself
How do catalysts work
Decrease activation energy by providing alternative pathway
Heterogenous catalyst definition
Catalyst is in different phase to reactants
Homogeneous catalyst definition
Catalyst is in same phase as reactants
Heterogeneous catalyst process
- Reactants ADSORB onto surface of catalyst on an active site.
- Reaction occurs on surface of catalyst.
- Products desorb from surface of catalyst.
How to make catalyst efficient
Increase SA
Spread catalyst over inert support medium
What happens when catalyst poisoning occurs?
Impurities can block active sites
Prevents reactants from adsorbing
Purifying reactants is the best way to prevent poisoning.
Examples of heterogeneous catalysts
- Making ammonia in Haber process CATALYSED BY IRON
N2 + 3H2 <–> 2NH3 - Making sulfuric acid in Contact process CATALYSED BY SOLID VANADIUM OXIDE (V2O5)
SO2+ V2O5 <–> SO3 + V2O4
2V2O4 + O2 <–> 2V2O5
overall: 2SO2 + O2 <–> 2SO3 - Manufacture of methanol
first forms synthesis gas: CH4 + H2O –> CO + 3H2
then reaction catalysed by solid chromium oxide Cr2O3: CO + 2H2 –> CH3OH
Example of homogeneous catalyst
Peroxodisulfate ions oxidise iodide ions to iodine.
Why does uncatalysed reaction of peroxodisulfate ions// ethanedioic acid have high activation energy?
Uncatalyzed has high activation energy because 2 negative ions repel.
Equations for example of homogeneous catalyst
Uncatalysed:
S2O8 2- + 2I- –> 2SO4 2- + I2
Catalysed by Fe2+:
1. S2O8 2- + 2Fe 2+ –> 2SO4 2- + 2Fe 3+
2. 2I- + 2Fe 3+ –> I2 + 2Fe 2+
Autocatalyst definition
One product of reaction catalysed reaction as it proceeds further.
Example of autocatalyst
Oxidation of ethanedioic acid by manganate ions
Equations for example of autocatalyst
Uncatalysed:
2MnO4 - + 16H+ + 5C2O4 2- –> 2Mn2+ + 8H2O + 10CO2
Catalysed:
1. 4Mn2+ + MnO4- + 8H+ –> 5Mn3+ + 4H2O
2. 2Mn3+ + C2O42- –> 2CO2 + 2Mn2+
Purple to clearer
Conc v time graph for this reaction
- Rate starts slow- no catalyst initially
- Two negatively charged reactants collide with a very high Ea
- Then some Mn2+ is formed, rate increases and reaction is being increasingly catalysed.
- Rate decreased and levels off at reactants used up.
