Transition Metals Flashcards
What is a transition metal?
Elements that can form 1 or more stable ions with partially filled 3d orbitals
Why is Sc not a transition metal?
Its ion Sc^3+ has an empty 3d orbital
What happens to electrons when forming an ion of a transition metal?
Electrons are removed from the 4s orbital before the 3d orbital
Why is Zn not a transition metal?
Its ion Zn^2+ has a full 3d orbital
What are the four main characteristics of transition metals?
- Form complex ions with ligands- Form coloured compounds- Have variable oxidation states- Show catalytic activity
How can the four main characteristics of transition metals be explained?
By the fact that their atoms and ions both have partially filled 3d orbitals
How do transition metals accept ligand coordinate bonds?
Transition metal ions use vacant, hybridised 4S, 4P and 4D orbitals to accept ligand coordinate bonds
What are hybridised orbitals?
Orbitals that have been reorganised to have the same energy
What is a ligand?
A species with a lone pair
How is a coordinate bond formed between a transition metal and a ligand?
The lone pair on the ligand is accepted by vacant orbitals (both electrons come from the same atom)
How many lone pairs can transition metals accept?
4 or 6
What is a monodentate ligand?
- 1 lone pair per ligand- 1 co-ordinate bond
What is a bidentate ligand?
- 2 lone pairs per ligand - 2 coordinate bonds
What is a multidentate ligand?
- Multiple lone pairs and coordinate bonds
What are the four shapes of complex ions?
- Octahedral- Tetrahedral- Square-planar - Linear
What is an octahedral complex ion?
- Co-ordination number = 6- 6 co-ordinate bonds- 90 degree bond angle between ligands
What ligands can form octahedral complex ions?
mono,bi and multidentate ligands
What is a tetrahedral complex ion?
- Co-ordination number = 4- 4 co-ordinate bonds- 109.5 degree bond angle between ligands
What ligands form tetrahedral complex ions?
Large and charged ions which repel one another
What is a square planar complex ion?
- Co-ordination number = 4- 4 co-ordinate bonds- 90 degree bond angle between ligands
What is an example of a square planar complex ion?
Cisplatin
What is a linear complex ion?
- Co-ordination number = 2- 2 co-ordinate bonds- 180 degree bond angle between ligands
What is an example of a linear complex ion?
Tollens reagent
<p>What is the complex ion formed between copper and water?</p>
<p>[Cu(H2O)6]2+</p>
<p></p>
<p>What state is[Cu(H2O)6]2+found in and why?</p>
<p>Aqueous because it has a charge</p>
<p>What is the colour of the[Cu(H2O)6]2+solution?</p>
<p>Light blue</p>
<p>What happens if excess Cl is added to[Cu(H2O)6]2+and how is Cl often added to the solution?</p>
<p>Cl is often added as HCl.</p>
<p>When added to[Cu(H2O)6]2+ Cl-causes ligand exchange to form [Cu(Cl)4]2-(aq) + 6H2O in a reversible reaction.</p>
<p>Because the Cl- ligandis large and charged, the co-ordination number is changed from 6 to 4 because of repulsion. This means the bond agle goes from 90 degrees to 109.5 degrees</p>
<p>What is the colour of[Cu(Cl)4]2-(aq)?</p>
<p>Solution is lime green</p>
<p>What happens to [Cu(H2O)6]2+if 2NH3(aq) are added?</p>
<p>The ligand NH3acts as a base and accepts 2 H+from 2 of the H2O ligands forming 2OH-ligands.</p>
<p>[Cu(H2O)6]2+ (aq)+ 2NH3(aq)⇒ [Cu(OH-)2(H2O)<span>4</span>] (s) + 2NH4+(aq)</p>
<p>What colour is[Cu(OH-)2(H2O)4] (s)</p>
<p>A light blue precipitate</p>
<p>What happens if excess ammonia (NH3) is added to either [Cu(H2O)6]2+ (aq) or [Cu(OH-)2(H2O)4] (s)</p>
<p>A royal blue solution of [Cu(H2O)2(NH3)4]2+(aq) and 4H2O is formed by ligand exchange</p>
<p>How can you go from [Cu(H2O)2(NH3)4]2+(aq)to [Cu(H2O)6]2+(aq)</p>
<p>Add excess water</p>
<p>What is the shape of [Cu(H2O)6]2+(aq)?</p>
<p>Octahedral</p>
<p>What is the shape of [Cu(H2O)2(NH3)4]2+(aq)?</p>
<p>Octahedral</p>
<p>What is the shape of [Cu(H2O)4(OH)2](s)?</p>
<p>Octahedral</p>
<p>What is the shape of [Cu(Cl)4]2- (aq)</p>
<p>Tetrahedral</p>
<p>What is [Co(H2O)6]2+(aq)?</p>
<p>An octohedral complex ion that forms a pink solution</p>
<p>What is [CoCl4]2-(aq)?</p>
<p>A tetrahedral complex ion that appears as a dark blue solution</p>
<p>What is [Co(NH3)6]2+(aq)?</p>
<p>A octahedral complex ion that appears as a light brown solution</p>
<p>What is [Co(OH)2(H2O)4] (s)?</p>
<p>An octahedral complex ion that appears as a green precipitate</p>
<p>What forms when excess Cl is added to [Co(H2O)6]2+(aq),how is the Cl added and what happens to the shape of the complex ion?</p>
<p>Cl is added in concHCl and a dark blue solution of [CoCl4]2-+ 6H2O is formed by ligand exchange in a reversible reaction (Add excess H2O to reverse). Due to Cl being large and charged shape changes from octahedral to tetrahedral because of repulsion, therefore coordination number is now 4</p>
<p>What happens when excess ammonia is added to [Co(H2O)6]2+?</p>
<p>A light brown solution of [Co(NH3)6]2+(aq) + 6H2O (l) is formed by ligand exhange in a reversible reaction (add excess H2O to reverse)</p>
<p>What happens when 2NH3are added to to [Co(H2O)6]2+(aq)?</p>
<p>A green precipitate of [Co(OH)2(H2O)4] (s) and 2NH4+is formed because NH3acts as a base and accepts 2 H+from 2 of the H2O ligands leaving two of them as OH and forming two ammonium ions</p>
<p>What happens to[Co(OH)2(H2O)4] (s) When excess ammonia (aq) is added?</p>
<p>A light brown solution of [Co(NH3)6]2+(aq) + 6H2O (l) forms</p>
<p>What is [Fe(H2O)6]3+?</p>
<p>A yellow orange solution of a octahedral complex ion</p>
<p>What is [FeCl4]-?</p>
<p>A yellow/brown solution of a tetrahedral complex ion</p>
<p>What is [Fe(OH)3(H2O)3]?</p>
<p>An orange brown precipitate of an octahedral complex</p>
<p>What happens if you add Cl to [Fe(H2O)6]3+(aq)?</p>
<p>Adding HCl causes ligand exchange to take place in a reversible reaction to form [FeCl4]-(aq) + 6H2O (l). Due to the Cl-ligand being large and charged complex shape is changed from octahedral to tetrahedral due to repulsion. Bond angle is now 109.5.</p>
<p>What happens if you add 3NH3to [Fe(H2O)6]3+(aq)?</p>
<p>The NH3ligand acts as a base and accepts 3 H+ions from 3 H2O ligands to form 3 OH-ligands. This creates a brown precipitate of [Fe(OH)3(H2O)3] (s) + 3NH4+(aq)</p>
<p>What happens if you add excessNH3to [Fe(H2O)6]3+(aq)?</p>
<p>Nothing,[Fe(H2O)3(OH)3]will not redisolve with excess NH3and ligand exchange will not take place</p>
What is a bidentate ligand?
A molecule that contains two atoms that can coordinately bond to a central ion in a complex using lone pairs
What are two examples of bidentate ligands?
- Ethan-1,2-diamine - Ethanedioate ion
What shaped complex ions do bidentate ligands form with transition metals?
Octahedral so bidentate ligands lie at 90 degrees to each other
What does the chelate effect mean in terms of ligand substitution?
Bidentate ligands will always be substituted in place of a monodentate ligand
What is a multidentate ligand?
A molecule than contains multiple atoms that can co-ordinately bond to a central ion in a complex
What are two examples of multidentate ligands?
EDTA and haemoglobin
What is EDTA?
- EthyleneDiamineTetraAcetic Acid- Can form 6 coordinate bonds- 4- charge
What does haemoglobin do?
Carries oxygen molecules around the body
What is the lower ligand of haemoglobin when deoxygenated?
H2O
What is the lower ligand of haemoglobin when oxygenated?
O2
What happens to haemoglobin in the presence of carbon monoxide?
Carbon monoxide coordinately bonds to haemoglobin in the same place that oxygen would. This bond is permanent and ligand exchange cannot take place
What is the chelate effect?
Bidentate and mutidentate ligands readily substitute/exchange in place of mono dentate ligands, creating a more stable complex
How can the chelate effect be explained
- Moles of product are higher than moles of reactant (increase in entropy), delta S is positive (reactions tend towards entropy increase - Enthalpy change (delta H) is negligible because the same number of coordinate bonds are broken and formed - delta G = delta H - (T x delta S), delta G will always be negative because of the negligible delta H, positive temp and positive delta S- Exchange always happens readily as it is feasible at any temperature
What types of isomerism can monodentate complexes show?
Cis-trans
When does cis-trans isomerism show in octahedral complexes?
When you have a 4:2 split in ligand type
What are cis isomers?
Same side
What are trans isomers?
Opposite side
When does cis-trans isomerism show in square planar complexes?
When you have a 2:2 split in ligand type
What is an example of a square planar complex that shows cis-trans isomerism?
Cisplatin and transplatin
What isomerism can bidentate complexes show?
Optical isomerism
Which bidentate complexes can show optical isomerism?
Any bidentate complex
What are three facts about optical isomers?
- non superimposable- will rotate plane polarised light- it is possible to haver a racemic mixture (equimolar concentrations of both)
Why are transition metal complexes coloured?
- They have partially filled d orbitals- When ligands coordinately bond they cause d orbitals to split from 1 energy level to 2- Frequencies of visible light cause 1 or 2 electrons to be promoted from the lower d orbitals (ground state) to a higher d orbital (excited state)- Energy difference between these orbitals is delta E- Delta E varies so the frequencies of visible light that are not absorbed are reflected
What is delta E affected by?
- Oxidation state of the transition metal ion- Type of ligand- Coordination number
What size delta E would you expect from a blue solution?
Blue has a high frequency, if blue is reflected then a lower wavelength is absorbed therefore the complex would have a lower delta E
The greater the delta E…
The greater the frequency of light absorbed
Name the colours from shortest to longest wavelength of light
ROYGBIV
How do you calculate delta E?
hf
What is delta E?
The difference in energy between split orbitals
What is h?
Planks constant (6.63 x 10^-34)
What if f?
Frequency (Hz)
How can you calculate frequency?
Speed of light / wavelength (m)
How do you convert from atoms to moles?
x Avogadros constant
How do you convert from nanometers to meters?
x 10^-9
How do you convert from joules to Kj?
/1000
What can transitional metals have?
Variable oxidation states
Why can transition metals have variable oxidation states?
4S electrons are lost before 3D electrons when ions form, this allows them to have a number of stable electronic configurations within the partially filled d orbitals
What trend do T.Ms follow from Ti to Mn?
Increase in number of stable oxidation states
What trend do T.Ms follow from Cu to Mn?
Increase in number of stable oxidation states
What do T.Ms do when they have a low oxidation state?
Act as reducing agents and tend to be oxidised to higher oxidation states
What do T.Ms do when they have a high oxidation state?
Act as oxidising agents and tend too be reduced to a lower oxidation state
What two factors affect the potential for a transition metal to be reduced from a higher to a lower oxidation state?
pH and ligand type
What is more likely to happen to transition metal ions in acidic conditions?
Reduced
What is more likely to happen to transition metal ions in alkaline conditions?
Oxidised
How does ligand type affect the REDOX potential of a T.M?
Some ligands for stronger coordinate bonds than others, the stronger the coordinate bond (enthalpy) the less likely the T.M is to be oxidised/reduced
How can vanadium be reduced by Zn(s)?
V can be reduced through 3 steps by Zn, from VO2^+(aq) to V^2+(aq) in acidic conditions
What are the stages of the reduction of vanadium by zinc?
1 - VO2^+(aq) to VO^2+(aq)2 - VO^2+(aq) to V^3+(aq)3 - V^3+(aq) to V^2+(aq)
What is the colour and oxidation state of V in VO2^+(aq)?
yellow and +5
What is the colour and oxidation state of V in VO^2+(aq)?
blue and +4
What is the colour and oxidation state of V^3+(aq)?
green and +3
What is the colour and oxidation state of V^2+(aq)?
violet and +2
What is oxidised?
Fe^2+ to Fe^3+
What is reduced?
Mn from +7(MnO4^-) to +2(Mn^2+)
What colour is MnO4^-?
Purple
What colour is Mn^2+?
Colourless
What are the conditions and how are the conditions achieved?
Acidic, added dilute H2SO4 to supply the H+ ions
What is the ratio of Fe^2+ to MnO4^-?
5:1
How do you carry out the titration?
1 - Fill burette with MnO4^- of a known conc2 - add a known volume of Fe^2+ (aq) (250cm^3)3 - Add MnO4^-, colour changed from purple to colourless as Fe^2+ is oxidised and MnO4^- is reduced4 - When Fe ^2+ runs out, colour change stops5 - When solution in flask stays purple the titration is done6 - nFe^2+ = nMnO4^- x 5
What is oxidised?
C in C2O4^2-
What is reduced?
Mn in MnO4^-
What is the colour change?
Purple to colourless
What is the mole ratio?
5C2O4^2- : 2MnO4^-
What goes in the flask?
Known volume of C2O4^2-
What goes in the burette?
Known conc and volume of MnO4^-
What is the reaction process?
- 2MnO4^- converted to Mn^2+ by C2O4^2– Purple to colourless
What is the mole calc?
nC2O4^2- = nMnO4^- x 2.5
What phase is the catalyst in?
A different phase to the reactants
What state is the catalyst usually?
A solid T.M in a (aq) or (g) reaction
What are two examples of heterogeneous catalysts?
Fe (s) in the Haber process and V2O5 (s) in the contact
Why are T.Ms used as heterogeneous catalysts?
Have multiple stable oxidation states
How can you increase the efficiency of a heterogeneous catalyst?
- Increase the surface area (powder)- Spread the catalyst over a support medium to increase efficiency (less catalyst over a bigger area)
Why does efficiency decrease over time?
“Poisoning” occurs due to impurities sticking to the surface and blocking the interaction between the catalyst and the reactants
What are homogeneous catalysts?
Catalysts that exist in the same phase as the reactants
What do catalysts do?
Provide a reaction pathway with lower activation energy from forming an intermediate in a two step reaction
When does autocatalysis occur?
When one of the products of a reaction acts as a catalyst for the reaction
Explain the graph of a reaction where autocatalysis is occuring
- Very slow rate when not a lot of product is produced- As product increases so does the rate (rapidly)- Reaction slows as the conc of reaction approaches 0
Why can autocatalysis take place?
T.Ms have variable stable oxidation states
