Transition metals Flashcards
What is a transition metal?
Incomplete d sub-shell
define ligand
an atom ion or molecule which can donate a lone electron pair
co-ordinate bonding definition
when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
co-ordination number definition
the number of co-ordinate bonds formed to a central metal ion
monodentate ligand defininton and examples
form one co-ordinate bond per ligand
h2o, nh3, cl-
bidentate def and examples
has two atoms with lone pairs and can form two coordinate bonds per ligand
e.g. NH2CH2CH2NH2 or C2O4 2-
multidentate def and example
forms more than 2 coordinate bonds per ligand
e.g. EDTA 4-
exchange of NH3 and H2O ligands
- since they are similar in size and are both uncharged, exchange doesnt change coordination number
- however it may be incomplete
equation for complete exchange of H2o and nh3 ligands
[Co(H2O)6] 2+ + 6NH3 –> [Co(NH3)6] 2+ + 6H2O
equation for incomplete exchange of H2O and NH3 ligands
[Cu(H2O)6] 2+ + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 4H2O
reactions with chloride ions theory q
- adding a high conc of chloride ions to an aqueous ion leads to a ligand substitution reaction
- the cl- ligand is larger than the H2O or NH3 ligand, and so the exchange may change coordiation number
general formula for the addition of conc HCL to aqueous TMsq
[X(H2O)6] 2+ + 4CL- —> [XCl4] (charge -4) + 6H2O
TM chloride + water
becomes the AQUEOUS [X(H2O)6]2+
formation of bidentate ligands
Ethane-1-2-diamine:
[Cu(H2O)6]2+ + 3NH2CH2CH2NH2 –> [Cu(NH2CH2CH2NH2)3]2+ + 6H2O
Ethanedioate:
[Cu(H2O)6]2+ + 3C2O4 2- –> [Cu(C2O4)3] 4- + 6H2O
when does partial substitution of ethanedioate ions occur
dilute aqueous solution is added to a soution containing aqueous copper 2 ions
formula for partial sibstitution of ethanedioate ions
must be copper 2
[Cu(H2O)6]2+ + 2C2O4 2- –> [Cu(C2O4)2(H2O)2]2- + 4H2O
formula of edta complexes
[Cu(H2O)6]2+ + EDTA 4- –> [Cu(EDTA)]2- + 6H2O
what causes colour changes
changes in:
- oxidation state
- co-ordination number
- ligand
transition metal + NaOH
if 2+ :
[X(H2O)6]2+ + 2OH- –> X(H2O)4(OH)2 + 2H2O
if 3+ :
[x(H2O)6]3+ + 3OH- –> X(H2O)3(OH)3 + 3H2O
colour: copper 2+ complex + NaOH
light blue solution to blue precipitate
colour: iron 2+ complex + NaOH
pale green solution to green precipitate
colour: iron 3+ complex + NaOH
orange / brown solution to orange / brown precipitate
colour: aluminium 3+ complex + NaOH
colourless solution to white precipitate
in excess NaOH, the white precipitate will redissolve to form a colourless solution
- Al(H2O)3(OH)3 + 3OH- –> [Al(OH)6]3- + 3H2O
transition metal complex + ammonia
If 2+ :
[X(H2O)6]2+ + 2NH3 –> X(H2O)4(OH)2 + 2NH4+
IF 3+ :
[X(H2O)6]3+ + 3NH3 –> x(H2O)3(OH)3 + 3NH4+
colour: copper 2+ complex + NH3
light blue solution to blue precipitate
colour: iron 2+ complex + NH3
green solution to green precipitate
colour: iron 3+ complex + NH3
orange / brown solution to brown precipitate
colour: aluminium 3+ complex + NH3
colourless solution to white precipitate that doesn’t redissolve in excess
transition metal complex + Na2CO3 (carbonate)
if 2+ :
[X(H2O)6] 2+ + CO3 2- –> XCO3 + 6H2O
IF 3+ :
2 [X(H2O)6]3+ + 3CO3 2- –> 2X(H2O)3(OH)3 + 3H2O + 3CO2
bubbles seen (CO2)
colour: aluminium 3+ complex + carbonate
colourless solution to white precipitate
colour: iron 3+ complex + carbonate
brown solution to brown precipitate
colour: copper 2+ complex + carbonate
blue solution to green precipitate
colour: iron 2+ complex + carbonate
green solution to green precipitate
ligand substitution reaction : no change in charge or co-ordination
substitute ammonia with water
[Co(H2O)6]2+ + 4NH3 –> [Co(NH3)4(H2O)2] 2+ + 4H2O
ligand substitution reaction : change in charge and co-ordination
water / ammonia to chloride
[Co(H2O)6]2+ + 4Cl- –> [CoCl4]2- + 6H2O
ligand substitution reaction : change in charge number only
substitute for ethanedioate
[Co(H2O)6]2+ + 3C2O4 2- –> [Co(C2O4)3]4- + 6H2O
ligand substitution reaction : large entropy change
substitute for EDTA
[Co(H2O)6] 2+ + EDTA 4- –> [CoEDTA] 2- + 6H2O
