5I- Transition Metals Flashcards
How are electrons arranged in transition metals
4s sub shell empties and fills before 3d subshell
This is also true for ions ie Fe 3+
Definition of a transition metal and which ones are they
Form at least 1 stable ion with a partly filled d subshell
Ti, V, Cr, Mn, Fe, Co, Ni, Cu
Not transition metals are below
Sc forms a 3+ ion, no electrons in d subshell
Zn forms a 2+ ion, d subshell is filled with 10 electrons
What properties do transition metals have
Complex formation, transition metal surrounded by other ions/molecules by coordinate bonds (ligands)
Formation of coloured ions, transition metals are coloured
Variable oxidation states, transition metals in compounds have multiple oxidation states, Cu+ and Cu2+
Catalytic activity, transition metals increase the rate of reaction without being used up
What’s a ligand
Molecule or ion forming a coordinate bond with a transition metal by donating a pair of electrons
What’s a complex
A central metal atom/ion surrounded by ligands
Coordination number
The number of coordinate bonds to the central metal atom/ion surrounded
What are monodentate ligands and give examples
Form one coordinate bond per ligand
H2O
NH3
Cl-
H2O and NH3 are a similar size and are uncharged
Cl- is a larger ligand than the other two
What happens to coordination number when NH3 and H2O are exchanged as ligands
NH3 and H2O can be exchanged without changing the coordination number however the substitution may be incomplete
Affects Cu2+ Co2+
[Co(H2O)6]2+ + 6NH3 —> [Co(NH3)6]2+ + 6H2O
And
[Cu(H2O)6]2+ + 4NH3 —> [Cu(NH3)4(H2O)2]2+ + 4H2O
What happens to coordination number if H2O and Cl- are exchanged
Adding conc HCL or saturated NaCl to an aq ion leads to ligand substitution
Coordination number changes
Affects Co2+ Cu2+ Fe3+
[Cu(H2O)6]2+ + 4Cl- —> [CuCl4]2- + 6H2O
[Co(H2O)6]2+ + 4Cl- —> [CoCl4]2- + 6H2O
[Fe(H2O)6]2+ + 4Cl- —> [FeCl4]2- + 6H2O
What’s a bidentate ligand and examples
Contain two atoms with lone pairs (one lone pair on each atom) which can form two coordinate bonds per ligand
NH2CH2CH2NH2
C2O4-
Lone pairs and structure of bidentate ligands
Mind map
Equations to show formation of bidentate complexes with NH2CH2CH2NH2 and C2O4 2-
[Cu(H2O)6]2+ + 3NH2CH2CH2NH2 —> [Cu(NH2CH2CH2NH2)3]2+ + 6H2O
[Cu(H2O)6]2+ + 3C2O4 2- —> [Cu(C2O4)3]4- + 6H2O
Equation and conditions for partial substitution of C2O4 2- ions
Dilute aq C2O4 2- added to aq Cu 2+
Water molecules are replaced
[Cu(H2O)6]2+ + 2C2O4 2- —> [Cu(C2O4)2(H2O)2]2- + 4H2O
What are multidentate ligands and give example
Give an equation to show formation of this ligand
More than two atoms with a lone pair of electrons which bond to a transition metal ion
EDTA 4-
[Cu(H2O)6]2+ + EDTA4- —> [Cu(EDTA)]2- + 6H2O
What’s haem
Fe2+ complex with a multidentate ligand
Oxygen forms a coordinate bond to Fe2+ in haemoglobin, oxygen can be transported in the blood
Why is carbon monoxide toxic
CO replaces the O2 which is coordinate bonded to the Fe2+ in haemoglobin
What’s the chelate effect and explain it
Bidentate and multidentate ligands replace monodentate ligands forming more stable complexes
Eg
[Cu(H2O)6]2+ + EDTA 4- —> [Cu(EDTA)]2- + 6H2O
Reactions have an increased entropy, more moles of product than reactant and therefore more disorder
Enthalpy change is small as there are a similar number of bonds in both complexes
Delta s (entropy) is positive, delta H (enthalpy) is 0, therefore delta G (gibs free energy) is negative
Shapes of complex ions
Etc etc etc
What complexes are formed by transition metal ions and small ligands
Name the ligands
Octahedral complexes
Forms 6 bonds, therefore a coordination number of 6
90° bond angle
NH3 and H2O
Bidentate ligands NH2CH2CH2NH2 and C2O4 2-
What type of isomerism do octahedral complexes display
Monodentate ligands display [E] [Z] isomerism
Bidentate ligands display optical isomerism
Why type of complex do larger ligands form with transition metal ions
Name the ligand
Tetrahedral complexes
4 bonding pairs, therefore coordination number of 4
Cl-
109.5° bond angle
What type of complexes are formed by Pt2+ and Ni2+ metal ions
Square planar
4 bonding pairs, therefore a coordination number of 4
90° bond angle
What type of isomerism do square planar complexes have
And what type of isomer is cis platin
[E] [Z]
Cisplatin is the cis isomer which is the [Z] isomer
What type of complexes do Ag+ metal ions form
Give an example of an Ag+ complex
Linear
2 bonding pairs, therefore a coordination number of 2
[Ag(NH3)2]+, used in tollens reagent
Why do transition metals have colours
Transition metals have part filled d orbitals
In a compound, other atoms nearby make the d orbital split causing it to have different energies
Some wavelengths of visible light is
absorbed
Electrons move from a lower energy level (ground state) to a higher energy level (excited state)
The change between the split orbitals is the energy change (^E)
Light energy transmitted or reflected gives the colour we see
Equation for energy change (^E)
^E = hv = hc/wavelength
^E energy change (J)
h= planks constant
v= frequency of light (Hz)
c= speed of light (m/s)
Wavelength= (m)
What does the colour of ions depend on
Oxidation state
Coordination number
Ligands
These cause ^E to change causing colour to change
What’s the absorption of light used in
Spectroscopy
How to determine the conc of coloured ions in a solution
Colourimeter
Light passes through a sample
Compare the absorbance value of unknown sample with that against a graph of known concentrations
What are the two types of catalysts
Homogenous and heterogenous
What’s a homogenous catalyst
The catalyst is in the same phase as the reactants
What’s a heterogenous catalyst
A catalyst in a different phase to the reactants
How does a heterogenous catalyst work
Occurs at active sites at the surface of catalyst
Reactants adsorb to the active site
Bonds in the reactants weaken and break, molecules held in the correct orientation or higher conc of reactants at the surface increase collision frequency
How is surface area of a heterogenous catalyst maximised to minimise cost
Use of a support medium
Rh is placed on a ceramic support in catalytic converters
What determines whether a metal has a string adsorbance or a low adsorbance
e- in the 3d and 4s sub shell
If adsorption is too strong products won’t be released
If adsorption is too weak reactants won’t be adsorbed
Ni and Pt have the correct strength
What is the catalyst for the contact process give eq
V2O5, it is regenerated
SO2 + V2O5 —> SO3 + V2O4
2V2O4 + O2 —> 2V2O5
Overall
2SO2 + O2 —> 2V2O5
What’s the catalyst for the haber process give eq
Fe
N2 + 3H2 —> 2NH3
What is a problem with heterogenous catalysts
Poisoning
Active sites blocked by impurities
Reduces efficiency, expensive to replace
Catalyst may also be lost from the support medium
How do homogenous catalysts work
Reaction proceeds through an intermediate species
The intermediate will have a diffferent oxidation state to the OG transition metal but at the end it will return to its initial oxidation state
What’s the catalyst for a reaction between S2O8 2- and I - give eq
Fe 2+
S2O8 2- + 2Fe 2+ —> 2SO4 2- + 2Fe 3+
2Fe 3+ + 2I - —> 2Fe 2+ + I2
Overall
S2O8 2- + 2I - —> 2SO4 2- + I2
Fe 3+ (123, I (1-) —> I2 using Fe 3+)
2Fe 3+ + 2I - —> 2Fe 2+ + I2
S2O8 2- + 2Fe 2+ —> 2SO4 2- + 2Fe 3+
Overall
S2O8 2- + 2I - —> 2SO4 2- + I2
Why is the reaction between I- and S2O8 2- ions slow
High activation energy is needed as there is repulsion between 2 -ve ions
How to workout out if a substance can be a homogenous catalyst
It’s electrode potential (E value) should lie in between the electrode potentials from the two reactants
Reactant with a more +ve electrode potential will be reduced
Reactant with a more -ve electrode potential will be oxidised after
What’s autocatalysis
One of the products from a reaction can catalyse the reaction
What’s the catalyst for C2O4 2- and MnO4 - give eq
Mn 2+
4Mn 2+ + MnO4- + 8H+ —> 5Mn 3+ + 4H2O
2Mn 3+ + C2O4 2- —> 2Mn 2+ + 2CO2
Overall
2MnO4 - + 5C2O4 2- 16H+ —> 2Mn 2+ + 10CO2 + 8H2O
Describe the rate of reaction between MnO4- and C2O4 2-
Slow initially as it is uncatalysed, two -ve ions require a high activation energy
Mn2+ ions produced act as an auto catalyst reaction begins to speed up
As MnO4 - conc drops reaction slows
What oxidation states do transition metals have
Variable oxidation states
What are common oxidation states for vanadium, give formula for them
Vanadium(V) is reduced by zinc in an acidic solution to produce vanadium (IV) (III) and (II)
V 2+ (oxidation state +2)
V 3+ (oxidation state +3)
VO 2+ (oxidation state +4)
What’s redox potential
The tendency of a species to be reduced by accepting e- or be oxidised by donating e-
What influences an transition metals ion changing from a higher oxidation state (+3) to a lower oxidation state (+2)
pH
Ligand
What is tollens reagent used to distinguish
Difference between aldehydes and ketones
Equations for the reaction of [Ag(NH3)2]+ tollens reagent
Reduction eq
[Ag(NH3)2]+ + e- —> Ag + 2NH3
Oxidation eq
CH3CHO + H2O —> CH2CO2H + 2H+ + 2e-
