I- Transition Metals Flashcards
What are transition metals?
metals that contain an incomplete d subshell in atoms/ ions
* top row (Sn-Cu) x Zn (∵ atom + ion have 10 e-)
Properties
- form coloured ions
- form complexes
- exhibit variable oxidation states
- show catalytic activity
eg.
- Ni- magarine prod
- V2O5- making SO3 for H2SO4
- Fe- Haber process –> NH3
- Pt, Pd- catalytic converters
Ligand
- particle w/ lone pair
- that form co-ordinate bond to metal
Complex
- metal ion w/ ligands
- co-ordinately bonded to it
Co-ordination no.
no. of coordinate bonds from ligands to metal ions
Lewis base
lp donor
eg. ligands, H2O
Lewis acid
lp acceptor
Calculating overall charge of a complex
overall charge = charge on metal ion + sum of ligand charges
Shapes of complexes w/ 4 & 6 co-ordinate bonds respectively
4- tetrahedral (most of the time)
6- octahedral
What is a ligand w/ 1 co-ordinate bond called?
unidentate ligand
What is a ligand w/ 2 co-ordinate bonds called?
bidentate ligand
What is a ligand w/ several co-ordinate bonds called?
multidentate ligand
What kind of complexes have a linear shape?
Ag+ complexes
eg. [Ag(NH3)2]+
What kind of complexes have a tertrahedral shape?
those w/ large ligands- eg. Cl-
eg. [CuCl4]2-
What kind of complexes have a square planar shape?
Pt2+ complexes
eg. [PtCl4]2-
What kind of complexes have an octahedral shape?
- those w/ 6 coordinate bonds
- most common
- eg. [Cu(H2O)6]2+
Ligands like CO: and CN:- bond permaently. Why is that a problem?
- strong bonds formed
- x respire if too many rbc bonded
How does cisplatin work (briefly)?
- cancer drug
- binds to guanine in DNA
- stops replication
Factors causing a colour change
Δ in:
1. metal ion
2. type of ligand attached
3. co-ordination no.
4. oxidation state of transition metal
sizes of H2O and Cl- ligands
- Cl- > H2O
–> Cl- replaces H2O - co no. ↓
- eg. [Co(H2O)6]2+ –> [CoCl4]2-
sizes of H2O and NH3 ligands
~
What is a partial substitution?
- some but x all ligands replaced
- eg. [Cu(H2O)6]2+ + 4NH3 –> [Cu(H2O)2(NH3)4]2+ + H2O
What does ‘en’ stand for in diagrams?
ethandioate ion
What is the chelate effect?
- small ΔH in sub reactions
- ∵ ~/ same no. of bonds broken + formed
- big ↑ in entropy (large +ve ΔS)
- products = thermodynamically ↑ stable than reactants
nm to m unit conversion
1 nm = 1 x 10^-9 m
What are d-d transitions?
- energy (in form of UV/ visible light) absorbed
- excites e- from lower d to higher d orbitals
Colour of species with no d electrons
- x colour
- ∵ x d e- to excite
Colour of species with 3d10
- x colour
- x vacant orbitals for e- to be promted to
Planck relation equation
E = hv = hc/ λ
- E = energy
- h = Planck constant (JHz/ Js)
- v = freq (Hz)
- c = speed of light (3 x 10^8 ms-1)
- λ = wavelength (m)
How does UV/ visible spectroscopy work?
- light passed thru complex
- amount passing thru measured (–> freq it absorbed)
Colorimetry
- ↑ conc ↑ absorbed
- ligand added to intensify colour of some ions (eg. bipyradine)
- strength of absorption of known conc measured –> graph
- conc of solution w/ unknown conc found by measuring absorption + using graph
What is a common oxidising agent used in redox titrations?
potassium manganate (VII), KMnO4
- MnO4 - + 8H+ + 5e- –> Mn2+ + 4H2O
State a suitable reagent used in a redox titration involving MnO4 -, to achieve acidic conditions.
dilute H2SO4
- x HCl – MnO4 - would oxidise Cl- –> Cl2
- x conc. H2SO4/ conc. HNO3 – oxidising agents themselves
- ==> affects vol of KMnO4 required
- x weak acids – x provide enough H+
5 C2O4 2- + 2MnO4 - + 16H+ –> 10CO2 + 2Mn2+ + 8H2O
Suggest why this reaction is slow to start.
2 -ve ions repel
In a reaction between Fe2+ and MnO4 -, what is done if Fe is not in the +2 oxidation state?
- if element Fe (0) –> reacted w/ H2SO4–> oxidised
- if Fe (+3) –> reacted w/ Zn –> reduced (remaining Zn must be removed to stop it reducing Fe3+ formed in titration back to Fe2+)
