Transition Metals Flashcards
What is a transition metal?
A metal that can form one or more stable ions with an incomplete sub shell
What should you remember when working out electron configuration?
4s fills and empties before 3D
What are the electron configurations of Cr and Cu?
[Ar]4s1 3d5
[Ar]4s1 3d10
What is the electron configuration of iron and it’s 2 common ions?
Fe [Ar]3d6 4s2
Fe 2+ [Ar] 3d6
Fe 3+ [Ar]3d5
What is the electron configuration of Sc and Sc3+?
[Ar] 4s2 3d1
[Ar]
What is are the electron configurations of Zn and Zn2+?
[Ar] 4s2 3d10
[Ar] 3d10
Why are Sc and Zn not transition metals?
Neither have an incomplete d sub shell in any of their ions
What is a ligand?
A particle with a lone pair which bonds to a metal by a coordinate bond
What is a complex?
A metal central ion which has got coordinately bonded ligands
What is the coordination number?
The number of coordinate bonds to the metal ion
What is a Lewis base?
A lone pair donor
What is a Lewis acid?
A lone pair acceptor
How do you describe a complex?
Write the metal Then the ligand molecules Then the number of ligands Then add a square brackets round Then add the charge [Cu(H2O)]2+
Describe a linear complex
Coordination number: 2
Shape: 2*180 degree angles
Occurrence: Ag+ complexes
Example: Tollens reagent - [Ag(NH3)2]+
Describe a square planar complex
Coordination number: 4
Shape: flat with 4*90 angles
Occurrence: Pt2+, Ni2+
Example: [Pt(Cl4)]2-
Describe a tetrahedral complex:
Coordination number: 4
Shape: triangle pyramid with bond angle of 109.5 degrees.
Occurrence: Cl- or larger charged ions
Example: [Cu(Cl4)]2-
Describe an octahedral complex
The most common Coordination number: 6 Shape: 90 degree angles Occurrence: most complexes with small ligands (H2O, NH3, OH-) Example: [Cu(H2O)6]2+
Why is a ligand monodentate?
Ions only form one ligand
What is an example of a monodentate ligand?
OH-
H2O
NH3
Cl-
What is a bidentate ligand?
An ligand that can form 2 coordinate bonds to a transition metal
How many coordinates can EDTA form?
6
What is it called when an ion can form more than two ligands to a transition metal?
Multidentate
How do you work out the oxidation state of a metal ion?
Total charge of the complex-the sum of the charges of the ligands Eg [Cu(H2O)]2+ \+2-0=+2 EG [Cu(H2O)4(OH-)2] 0- -2= +2
In which complexes can you observe stereoisomerism?
Square planar
Octahedral
Two complexes have the same formula but different orientations in space, what are they?
Optical isomers so they are enantiomers of each other
What is optical isomerism?
Two non-superimposable mirror images
Why does a transition metal complex change colour?
Change in oxidation state
Change in ligand
Change in the coordination number
Why are transition metal complex ions coloured?
-Only transition metal complexes ions have colours.
-the d orbitals split into 2 sets as the electrons from the
ligands interfere with it.
- this creates a set of 3 orbitals and a set of 2 orbitals
-These sets are at different energy levels - the 3-orbital set is at a lower energy level than the 2-orbital set.
-Hence, a specific amount of energy is needed for an electron to move from the lower orbitals to the higher orbitals.
-When light is shone onto the complex ion, certain frequencies of light are absorbed the which promotes an electron to a ‘higher’ orbital
-Any light which is not absorbed is the colour of the complex ion as the non-absorbed light is reflected back into our eyes
What equation can be used to work out the energy difference between the ground state and the
excited state of the d electrons?
∆E = hν = hc/λ h- planks constant v(miu)- frequency of light absorbed λ- wavelength c- is speed of light
what is a d to d transition?
when an electron in the 3 orbital set of electrons is promoted to the 2 orbital set when its excited by light
How can you use colorimetry to identify the concentration of a transition metal ion complex?
- zero the calorimeter
- take know conc of solution
- measure the absorbance of known solution
- plot a calibration curve
- all light should be passed through a filter
- Which is passed through the sample
- plot relative absorbance against concentration of know solution
- identify sample absorbance to extract concentration
What is the colour and oxidation state of VO2^+?
Yellow +5
What is the colour and oxidation state of VO^+2?
Blue +4
What is the oxidation state and colour of V^3+?
Green +3
What is the colour and oxidation state of V^2+?
Violet 2+
How do you react vanadium with zinc?
Produce a half equation for each then add them
Zinc reduces vanadium to a lower oxidation state
Acidic conditions favour which reaction?
Reduction
Alkaline conditions favour which reaction?
Oxidation
Why does tollens reagent turn silver?
It gets oxidised by the aldehyde and it’s a transition metal ion complex
What is the equation for the oxidation of tollens reagent?
RCHO+2[Ag(NH3)2]+3OH- to RCOOH+ 2Ag+ 4NH3+2H2O
When is a metal aqua ion soluble?
When it has a charge
No charge - not soluble
A neutral metal aqua ion forms what?
An insoluble precipitate
How can you tell if a reaction is acid base reaction or a ligand substitution?
If the molecule you react with the ligand becomes part of it it’s a ligand substitution, if it doesn’t it’s an acid base reaction
What is an acid base reaction?
Accepts or donated protons
Required practical: how do you identify unknown metal ion?
To each test tube add sample of unknown solution
To the first test tube add dropwise NaOH
The second dropwise NH3
The third dropwise NaCO3
Record observations for each
What colours are iron 2 copper 2 iron 3 aluminium 3 as aqueous ions?
Iron 2-green solution
Copper 2- blue solution
Iron 3- purple solution (can look yellow brown)
Aluminium 3- colourless solution
What is formed and what colour when iron 2 copper 2 iron 3 aluminium 3 as aqueous ions turn when NaOH is added?
Each remain the same colour as their iron and form instead a precipitate
Except iron 3 which forms a brown precipitate
Iron 2 precipitate goes brown standing in air
The Aluminium precipitate is white
The iron 2 precipitate is green
What happens when iron 2 copper 2 iron 3 aluminium 3 an excess of NaOH is added to the NaOH precipitates?
They all remain the same except aluminium 3 which returns to a colourless solution as when it was an ion
What happens when dilute NH3 is added to the iron 2 copper 2 iron 3 aluminium 3 precipitates of NaOH?
Iron 2-green precipitate remains, but goes brown standing in air
Copper 2- remains blue precipitate
Iron 3- remains brown precipitate
Aluminium 3- reforms white precipitate
What happens when excess dilute NH3 is added in excess to the iron 2 copper 2 iron 3 aluminium 3 precipitates of NaOH?
No further change
Except copper 2 turns deeper blue
What happens when Na2CO3 is added to iron 2 copper 2 iron 3 aluminium 3 solutions and precipitates of excess NH3 ?
Iron 2- remains green precipitate, but doesn’t go brown in air
Copper 2- turns to blue green precipitate
Iron 3- remains brown precipitate, but CO2 gas is evolved
Aluminium 3- remains white precipitate but CO2 gas is evolved
Why might the iron 3 aqueous ion look yellow brown instead of purple?
Some [Fe(H20)5(OH)]2+ may be present
What is the formula of the aqueous iron 2 ion?
[Fe(H2O)6]2+ (aq)
What is the formula of the copper 2 aqueous ion?
[Cu(H2O)6]2+
What is the formula of the iron 3 aqueous ion?
[Fe(H2O)6]3+
What is the formula of the aluminium 3 aqueous ion?
[Al(H2O)6]3+
Give the formulae for the reactions of iron 2 and 3 with OH- ions:
[Fe(H2O)6]2+(aq) + 2OH–(aq) ==> Fe(H2O)4(OH)2 + 2H2O(l)
[Fe(H2O)6]3+(aq) + 3OH–(aq) ==> Fe(H2O)3(OH)3 + 3H2O(l)
Give the formulae for the reactions of copper 2 and aluminium 3 with OH- ions:
[Cu(H20)6]2+(aq) + 2OH–(aq) ==> Cu(OH)2(H2O)4 + 2H20
[Al(H2O)6]3+(aq) + 3OH–(aq) ==> Al(OH)3(H2O)3 + 3H2O(l)
what is the equation for aluminium in excess NaOH?
Al(OH)3(H20)3 + 3OH-(aq) to [Al(OH)6]3-(aq) + 3H2O(l)
White precipitate to colourless solution
Why does aluminium react in NaOH and excess NaOH?
it’s amphoteric it also reacts with acids
[Al(OH)3(H2O)3}(s) + 3H+ to [Al(H2O)6]3+ (aq)
Give the formulae for the reactions of iron 2 and 3 with NH3:
[Fe(H2O)6]2+(aq) + 2NH3(aq) to [Fe(H2O)4(OH)2] (s)+ 2NH4+(aq)
[Fe(H2O)6]3+(aq) + 3NH3(aq) to Fe(H2O)3(OH)3 + 3NH4+(aq)
Give the formulae for the reactions of copper 2 and aluminium 3 with NH3:
[Cu(H20)6]2+(aq) +2NH3(aq) to Cu(H20)4(OH)2 + 2NH4+(aq)
[Al(H2O)6]3+(aq) + 3NH3(aq) to Al(H2O)3(OH)3 + 3NH4+(aq)
Give the formula for the reaction of copper 2 and NH3 in excess:
Cu(H2O)4(OH)2 + 4NH3(aq) to [Cu(NH3)4(H2O)2]2+(aq) + 2OH–(aq) + 2H2O(l)
Give the formulae for the reactions of iron 2 and 3 with Na2CO3:
[Fe(H2O)6]2+(aq) + CO3 2- (aq) to FeCO3(s) + 6H2O(l)
2[Fe(H2O)6]3+(aq) + 3CO3 2- (aq) to 2Fe(H2O)3(OH)3 + 3CO2(g) + 3H2O(l)
Give the formulae for the reactions of copper 2 and aluminium 3 with Na2CO3:
[Cu(H2O)6]2+ (aq) + CO3 2- (aq) to CuCO3(s) + 6H2O(l)
2[Al(H2O)6]3+(aq) + 3CO3 2- (aq) to 2Al(H2O)3(OH)3 + 3CO2(g) + 3H2O(l)
How do we know 3+ ions are more acidic?
they react with CO3 2- ions in an acid-base reaction whereas the 2+ ions go through ligand substitution reactions
Why are 3+ ions more acidic?
they have a greater charge desity so a stronger inductive effect which draws electrons in to the metal weakening the O-H bond Allowing H+ to be released more freely therefore its a strionger acid
Give the equation for the ligand substitution of conc HCl with hexaaqua cooper :
[Cu(H20)6]2+ +4Cl- to 6H20 + [CuCl4]2-
Give the ligand substitution of haemoglobin:
And haemoglobin structure
Why is CO dangerous?
Made up of a porphyrin ring surrounding a central Fe2+ ion with a H20 ligand 4 N lingands and one N attached to a glob in molecule
Water exchanges with oxygen
Oxygen used up and so becomes water again
Carbon monoxide is dangerous bc it binds irreversibly to haemoglobin as it has a stronger dative covalent bond
So it the iron molecule have been poisoned
What is disproportionation?
when a species is simultaneously oxidised and reduced
to form more stable forms
Why is aqueous copper chemistry limited?
It is disproportionated
