Transition metals Flashcards
What is a transition element?
- element that forms at least one stable ion
- with partially filled d sub-shell
Why is scandium not a transition metal?
- does not have partially filled d sub-shell
- only forms one ion Sc3+
Why is zinc not a transition metal?
- full d sub-shell
- Zn+ = only ion formed
What are the key features of transition elements?
- complex ions formed
- coloured ions formed
- catalytic properties
- variable oxidation states
what is a co-ordinate bond?
- shared pair of electrons
- both from same atom
what is a ligand?
- ion/molecule with lone pair of e-
- can form co-ordinate bond with transition metal ion
- e.g. H2O
what is a bidentate ligand?
- ion/molecule with 2 lone pairs of e-
- on two different atoms
- each forms co-ordinate bond with metal ion
what is a co-ordination number?
number of bonds a transition metal forms
what is a complex ion?
central atom/ion surrounded by ligands
what is the electron configuration of copper?
1s2 2s2 2p6 3s2 3p6 3d10 4s1
what is the rule for electron configurations of transition metal ions?
First in - First out
4s sub-shell empties first
What are the 3 types of ligands that transition metals can form?
- monodentate = each ligand forms 1 co-ordinate bond
- bidentate = each ligand forms 2 co-ordinate bonds
- multidentate = each ligand forms 2 or more co-ordinate bonds
What are the 3 monodentate ligands?
- NH3
- H2O
- Cl-
What are the two bidentate ligands?
- Ethane-1,2-diamine OR 1,2-diaminoethane
H2:N-CH2-CH2-N:H2 - ethandioate ion
What are the 4 shapes that transition metals form?
- Octahedral
- Tetrahedral
- Square planar
- Linear
What is an example of an octahedral complex?
- [Cu(H2O)6] 2+
- H2O = no charge
- overall charge = 2+
- oxidation state of Cu = 2+
What is an example of a tetrahedral complex?
- [CoCl4] 2-
- Cl- = 1- charge
- overall charge - 2-
- oxidation state of Co = 2+
- Cl- ions = relatively large
What is an example of a square planar complex?
- [Ni(CN)4] 2-
- CN = 1- charge
- overall charge = 2+
- oxidation state of Ni = 2+
What is an example of a linear complex?
- [Ag(NH3)2] +
- NH3 = no charge
- overall charge = 1+
- oxidation state of Ag = 1+
What is an example of a bidentate octahedral complex?
- [Ni(NH2CH2CH2NH2)3] 2+
- oxidation state of Ni = 2+
Copper(I) iodide is a white solid. Explain why copper(I) iodide is white
- Full (3)d (sub)shell or (3)d10
- No (d-d) transitions possible/ cannot absorb visible/white light
[EDTA] 4-
- hexadentate ligand
- can form 6 coordinate bonds
- 2 from N atoms
- 4 from O- atoms
[Cu(H2O)6]2+ —-> [Cu(H2O)2(NH3)4) 2+
ligand substitution
[Cu(H2O)6]2+ + 4NH3 —> [Cu(H2O)2(NH3)4] 2+ + 4H2O
ligand substitution with [Cu(H2O)6]2+ and CN
[Cu(H2O)6]2+ + CN —> [Cu(H2O)5 CN]+ + H2O
what is the chelate effect
- mono dentate ligand
- replaced by bidentate/multidentate ligand
[Cu(H2O)6]2+ and NH2CH2CH2NH2 chelate effect
[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 —> [Cu(H2NCH2CH2NH2)3] 2+ + 6H2O
[Cu(H2O)6]2+ and NH2CH2CH2NH2 chelate effect
describe entropy change in this reaction
[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 —> [Cu(H2NCH2CH2NH2)3] 2+ + 6H2O
- 4 moles on left
- 7 moles on right
- increase in entropy
- thermodynamically more favourable
- large increase in entropy = chelate effect
[Co(NH3)6] 2+ and EDTA 4-
chelate effect
[Co(NH3)6] 2+ + EDTA 4- —> [CoEDTA] 2- + 6NH3
[Co(NH3)6] 2+ and EDTA 4-
chelate effect
describe entropy change
[Co(NH3)6] 2+ + EDTA 4- —> [CoEDTA] 2- + 6NH3
- 2 moles on left
- 7 moles on right
- large increase in entropy
- thermodynamically favourable
[Cu(NH3)6] 2+ + 3H2NCH2CH2NH2 —> [Cu(H2NCH2CH2NH2)3] 2+ + 6NH3
explain why this reaction is feasible
- enthalpy change = 0
- same number of Cu-N bonds broken and made
- 7 molecules produced from 4 molecules
- large increase in entropy
- delta G will be negative
- so reaction is feasible
[Cu(H2O)6] 2+ + 4Cl- —>
[CuCl4] 2- + 6H2O
Haemoglobin
- 4 co-ordinate bonds between Fe2+ N atoms in the haem structure
- 1 co-ordinate bond with globin (protein)
- 1 co-ordinate bond between O2 and Fe2+
- O2 forms a co-ordinate bond to Fe2+ in haemoglobin enabling oxygen to be transported in the blood
- CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin.
This prevents O2 from bonding to the Fe2+, causing suffocation
2 types of isomerism shown by transition metals
- stereoisomerism
- optical isomerism
stereoisomerism
same structural formula but different arrangement of carbon atoms in space
cis/trans isomerism
- 4 of one type of ligand
- 2 of another
- octahedral complexes
- 2 ligands 180 degrees opposite eo = trans isomerism
- 2 ligands 90 degrees next to eo = cis isomerism
example of octahedral cis/trans isomerism
[CoCl2(NH3)4] +
example of square planar cis/trams isomerism
[PtCl2(NH3)2]
cisplatin
- cis isomer of [PtCl2(NH3)2]
- effective anti cancer drug
- binds to DNA in cells and stops replication
- two Cl- ions substituted for 2 N atoms on adjacent guanine bases
example of bidentate cis/trans isomerism
[Cr(H2O)2(C2O4)2] -
oxidation state of Cr = +3
co-ordination number = 6
cis isomer of [Cr(H2O)2(C2O4)2] - also displays
optical isomerism
optical isomerism
- occurs with at least 2 bidentate ligands
- 2 bidentate ligands and 2 mono dentate = structure has to be cis to be optical
ROY G BIV
ROY = low energy
BIV = high energy
why does KMnO4 appear purple
- contains Mn2+
- absorbs yellow and green
- remaining colours reflected
why does CuSO4 appear blue
- absorbs ROYG
- remaining colours make it appear blue
why are transition metals coloured
partially filled d-sub shells
ground state
all d orbitals are of equal energy
when transition metal moves from lower energy orbital to higher energy orbital
- energy taken from white light
- absorbed light is missing
- reflected light gives compound colour
frequency of light equation
energy change (joules) = Planck constant x frequency of light (Hz)
wavelength of light equation
energy change (joules) = Planck constant x (speed of light/wavelength of light)
if transition metal has large change in energy
- high energy light BIV absorbed to excite electrons
- ROY reflected
- compound will look red/orange
if transition metal has low change in energy
- low energy light ROY absorbed to excite electrons
- BIV reflected
- compound will appear blue/purple
change in energy leading change in colour means
LOCoS
- change in ligands
- change in oxidation states
- change in co-ordination number
- change in shape of complex
[VO2(H2O)4]+ colour
oxidation state +5
(VO2) + = yellow
[VO(H2O)5]2+ colour
oxidation state +4
VO2+ = blue
[V(H2O)6]3+ colour
oxidation state +3
V3+ = green
[V(H2O)6]2+ colour
oxidation state +2
V2+ = violet
transmittance readings
1.0 = all light passed through none absorbed
0.5 = some light passed through some absorbed
0.0 = all light absorbed by transition metal compound
to find unknown concentration of sample from calibration curve
- measure absorbance for a range of known concentrations
- plot graph of absorbance against concentration
- read value of concentration for the measured absorbance from the graph
what is a catalyst
chemical/substance that speeds up rate of reaction without being used up
how do catalysts work
provides alternative pathway with lower activation energy
heterogenous catalyst
catalyst in different phase to reactants
homogenous catalyst
catalyst in same phase as reactants
heterogeneous catalysis process
- reactants adsorb onto surface of catalyst on an active site
- reaction occurs on the surface of the catalyst
- products desorb from surface of catalyst
making catalysts efficient
- increase surface area
- spread catalyst over an inert support medium
catalyst poisoning
- impurities can block active sites
- prevents reactants adsorbing
- purifying reactants to prevent poisoning
heterogenous catalyst example haber process
N2 (g) + 3H2 (g) —-> 2NH3 (g)
catalysed by SOLID IRON
heterogeneous catalyst example contact process
catalyst V2O5
sulphuric acid made
step 1
SO2 (g) + V2O5 (s) —> SO3 (g) + V2O4 (s)
step 2
2V2O4 (s) + O2 (g) —> 2V2O5 (s)
overall reaction
2SO2 (g) + O2 (g) —> 2SO3 (g)
sulfuric acid then made when SO3 reacts with H2O
heterogenous catalyst manufacture with methanol
step 1
CH4 (g) + H2O (g) —> CO (g) + 3H2 (g)
step 2
CO (g) + 2H2 (g) —> CH3OH
catalysed by chromium oxide Cr2O3
why do transition metals act as catalysts
they have variable oxidation states
homogenous catalysts
uncatalysed reaction
S2O8 2- (aq) + 2I- (aq) —> 2SO4 2- (aq) + I2 (aq)
high activation energy due to 2 negative ions repelling eo
step 1
S2O8 2- (aq) + 2Fe 2+(aq) —> 2SO4 2- (aq) + 2 Fe 3+ (aq)
step 2
2Fe 3+ (aq) + 2I- (aq) —> I2 (aq) + 2Fe 2+ (aq)
Fe2+ catalyst regenerated in second step
autocatalysis
- example of homogenous catalyst
- when one of the products of the reaction catalyses the reaction
autocatalysis
uncatalysed reaction:
2MnO4- + 16H+ + 5C2O4 2- —> 2Mn2+ + 8H2O + 10CO2
step 1:
4Mn2+ + MnO4 - + 8H+ —> 5Mn3+ + 4H2O
step 2:
2Mn3+ + C2O4 2- —> 2Mn2+ + 2CO2
autocatalysis - why is initial rate of reaction slow
- both ions negative so they repel
- high activation energy
autocatalysis colour change
purple to clear
