Summary A* GRADE AQA A-Level Chemistry: Inorganic - Transition Metals (3.2.5)

1. Transition metals: Ti – Cu = incomplete d sub-level in atoms/ions
form positive ions: s electrons removed before d electrons
not Sc & Zn: Sc3+ & Zn2+ = empty/full 3d subshell

Physical Properties – similar (don’t change across period)
- High density
- High melting point
- Similar ionic radius
Chemical Properties
 complex formation
 formation of coloured ions
 variable oxidation states (unlike s-block metals)
 catalytic activity

Ligand: molecule/ion that forms co-ordinate bond with transition metal by donating pair
Complex: central metal atom/ion surrounded by co-ordinately-bonded ligands
Co-ordination number: number of co-ordinate bonds to central metal atom/ion



2. Substitution reactions

monodentate ligands: H2O, NH3, Cl-
NH3 & H2O: similar size & uncharged – no co-ordination number / shape change
- [Co(H2O)6]2+ (pink) + 6NH3 -> [Co(NH3)6]2+ (straw) + 6H2O
- Incomplete substitution:
[Cu(H2O)6]2+ (blue) + excess 4NH3 -> [Cu(NH3)4(H2O)2]2+ (dark blue) + 4H2O

Cl-: larger & charged – change of co-ordination number & shape
- [Co(H2O)6]2+ (pink octahedral) + 4Cl- -> [CoCl4]2- (blue tetrahedral) + 6H2O
- [Cu(H2O)6]2+ (blue octahedral) + 4Cl- -> [CuCl4]2- (yellow/green tetrahedral) + 6H2O
- [Fe(H2O)6]3+ (yellow octahedral) + 4Cl- -> [FeCl4]- (yellow tetrahedral) + 6H2O

bidentate ligands: H2NCH2CH2NH2 (ethane-1,2-diamine) & C2O42- (ethane dioate)
multidentate ligands: EDTA4-


Chelate effect
- bidentate/multidentate replace monodentate ligands = no. particles in solution increases
= greater entropy (more stable) = more feasible Gibbs
= hard to reverse – decrease entropy / if stronger newer bond
o negligible ∆H: made/broken bonds = similar/same strength / number / type


Haemoglobin: Fe2+ complex (6) = Haem (4 N: multidentate ligand) + N: globin protein + H 2O:/:O2
- H2O/O2 exchange to load/unload O2
- CO ligand replaces O2 = carboxyhaemoglobin
o strong ligand – doesn’t readily exchange with H2O/O2 ligands = Hb can’t transport O2
o toxic: starves organs of O2 = headaches, dizziness, unconsciousness, death

, 3. complex ion shapes
Octahedral 6 – small ligands (H2O / NH3)
- 6 monodentate ligands = cis-trans isomerism
- 3 bidentate ligands (NH2-CH2-CH2-NH2) = optical isomerism
- 1 hexadentate (EDTA4-) = optical isomerism

Tetrahedral 4 – larger ligands (Cl-)

Square planar 4 = cis-trans isomerism
Cisplatin: cis isomer

Linear: Tollen’s reagent [Ag(NH3)2]+




4. Formation of coloured ions by visible light
- ligands split 3d orbitals into 2 energy levels = ground state & excited state = energy gap ∆E
- electrons absorb energy from visible light frequencies = excite electrons
- transmitted/reflected visible light frequencies: combine = complementary colour – seen



∆E = hν = hc
λ
- ∆E: energy gap between ground & excited state d electrons
o larger = absorbs higher frequency
- h: Planck’s constant 6.63x10-34 J s
- v: frequency absorbed Hz
- c: speed of light 3x108 ms-1
- λ: wavelength absorbed m

things that cause a change in ∆E (that causes a colour change)
- oxidation state
- co-ordination number
- ligand




spectroscopy: find concentration of coloured ions in solution by measuring how much light absorbed
1. Colorimetry
- white light
- filter – colour of light sample absorbs
- solution
- colorimeter: calculates how much light absorbed by sample
2. Calibration curve: relative absorbance / concentration
3. Find concentration from absorbance of sample
Absorbs more light = more concentrated