Transition Metals Flashcards
What are transition metals?
Metals that can form one or more stable ions with an incomplete d sub-shell
Why are Sc and Zn d-block elements, yet not transition metals?
Their highest energy electron is in the de subshell
Not trabsition metals because do not form an stable ipn with an incomplete d subshell
What are four characteristic properties lf transition metals that arise due to their incomplete d subshell?
Complex formation
Catalytic activity
Variable oxidation states
Formation of coloured ions
What is a complex?
A central metal ion that is surrounded by ligands
What is a ligand?
A molecule or ion that forms a co-ordinate bond with a transition metal, by donating a pair of electrons
What are the three types of ligands?
Monodentate, bidentate, multidentate
What is a monodentate ligand?
A molecule or ion that donates one pair of electrons to the central metal ion to form one coordinate bond
Give four common monodentate ligands, and state where their lone pair of electrons is
Water- on the oxygen
Ammonia- on the nitrogen
Chloride ions- on the chloride
Cyanide ion- on the carbon
What is a bidentate ligand?
Molecules or ions that have two atoms, that can each donate a pair of electrons to the central metal ion to form two different coordinate bonds
What is a multidentate ligand?
A molecule or ion that has more than two atoms that can each donate a pair of electrons to the central metal ion to form more than two coordinate bonds
Give the name of the main multidentate ligand, how many coordinate bonds can ot form?
EDTA 4-
Can form six bonds
What is a coordinate number?
The number of coordinate bonds to the central ion in a complex
What are the four common shapes of complexes, and their bond angles and coordinate numbers?
Octahedral- 90, 6 bonds
Tetrahedral- 109.5, 4 bonds
Square planar- 90/180, 4 bonds
Linear- 180*, 2 bonds
What shape do complexes containing water ligands usually have?
Octahedral
What shape do complexes containing ammonia oigands usually have?
Octahedral
What shape do complexes containing chloride ligands usually have?
Tetrahedral
Why is there a difference between the shape of complexes containing chloride ligands and ammonia/water ligands?
Chlorine ions are much bigger than water or ammonia molecules
What shape do complexes containing copper(I) ligands usually have?
Linear
What shape do complexes containing silver(I) ligands usually have?
Linear
What is the complex product when silver chloride or silver bromide is dissolved in ammonia? What shape complex is it?
[Ag(NH3)3]+
Linear
What transition metals usually form complexes with square planar shapes?
Ni, Pt, Pd
Why do transition metals have coloured ions?
Transitipn metal ions can absorb a certain frequency of visible light
This causes d- subshell electrons to be promoted (as they gain energy)
The remaining frequencies of light are transmitted- and the ion appears this colour
What colour are aqueous copper (II) ions and why?
Blue
Cu 2+ ions absorb certain frequencies of visible light
D electrons are promoted
Remaining frequencies are transmitted in the blue area of the visible spectrum
What is the difference in d- orbital energy between transition metal atoms and in complexes?
In transition metal atoms, all d-orbitals have the same energy
In complexes, the d orbitals split depending on the coordination number. So some orbitals have more energy than others. The orbital split creates an energy gap (ΔE)
What is the frequency of loght absorbed by a transition metal ion dependent on?
The size of the energy gap (ΔE)- which is dependent on the coordination number of a complex
Give the two equations for ΔE, and the units of each measurment
ΔE= h (Js) x v (Hz)
ΔE= h x c (ms-1)/y (m)
What is the equation for frequency of light absorbed? (V)
V= c/ y
= speed lf light/ wavelength
In the equation for frequency, what is the unit for wavelength?
metres
What is the unit for energy gap (ΔE)
Joules
What three factors can affect the colour of transiripn metal complexes?
Coordination numbers
Ligand substitution
Oxidation states of transition metals
How does the change in coordination number affect the colour of a trabsirion metal ion?
The splitting of the d-orbitals is different in octahedrals and tetrahedrals- so changes the energy gap. Change in coordination number changes the shape, and so changes energy gap and frequencies of visible light absorbed/ transmitted
How does the change in ligand affect the colour of a trabsirion metal ion?
Different ligands change the energies lf the d orbitals, so changes the size of the energy gap and therefore the frequencies of visible light transmitted/ absorbed
How does the change in oxidation state affect the colour of a trabsirion metal ion?
As the oxidation state of a transition metal increases, so does the size of the energy gap. So different frequencies of visible light are absorbed/ transmitted
What is a colorimeter?
A type of spectroscopy that measures the amount of light absorbed by a solution, and goves a measure of concentration
How do you find the concentration of an unknown solution, using a colorimeter and a calibration curve?
Create 4/5 standard solutions of known concentrations
Select the filter of the complimentary colour to the metal ion, and measure the absorbance pf the known solutions
Use these results to plot a calobration curve
Compare an unknown solutions absorbance to the curve to find the conc.
When creating a calibration curve, why must 4/5 standard solutipns be made?
Sonthere are enough points to plot the curve, and a line of best fit can be drawn
Why is a filter used in a colorimeter?
The sample will only absorb certain frequencies of visible light. A filter that has a complimentary colour is used so the sample will absorb all the light
What is the equation and observations when aqueous cobalt (II) salts react with excess ammonia?
[Co(H2O)6]2+ + 6NH3 <—> [Cu(NH3)6]2+ + 6H2O
Pink to pale brown
Give the equation and observations when aqueous copper (II) salts react with excess ammonia?
[Cu(H2O)6]2+ + 4NH3 <—> [Cu(H2O)2(NH3)4]2+ + 4H2O
Blue to deep blue
What is the equations and observations when aqueous cobalt salts react with excess HCl?
[Co(H2O)6]2+ + 4Cl- <—> [CoCl4]2- + 6H2O
Pink to blue
What is the equation and observations when aqueous copper salts react with excess HCl?
[Cu(H2O)6]2+ + 4Cl- <—> [CuCl4]2- + 6H2O
Blue to yellow/green
What is the equation when aqueous iron salts react with excess HCl?
[Fe(H2O)6]2+ + 4Cl- <—> [FeCl4]2- + 6H2O
Describe how haem groups in haemoglobin are complexes?
They have multidentate ligands, coordination of 4
Iron is the complex in the centre
Square planar shape
Lone pairs of electrons on the 4 nitrogen’s form coordination bonds
The haem unit is then bound to a complex protein called globin
Describe the ligand substitution when haemoglobin binds to oxygen
In the lungs the concentration of oxygen is high, and the equilibrium shifts to the right. Water ligands are substituted for oxygen to form oxyhemoglobin.
The coordination number changes from 4 to 6
What is the chelate effect in ligand substitutions?
When a monodentate ligand is substituted by a bidentate or multidentate ligand, there is an increase in ΔS.
So ΔG is -ve and reaction is always feasible. The new complex formed is more stable
In a ligand substitution reaction, when will ΔH be 0?
When there are the same types and number of bonds being broken and formed
Describe the two types of stereoisomers of transition metal complexes with a square planar shape?
Cis-isomers- two different ligands. The same types of ligands are next to each other
Trans-isomers- two different ligands. The same types of ligands are opposite each other (ligands alternate)
Describe the two types of stereoisomers in transition metal complexes with an octahedral shape?
Occurs when there are four of one type of ligand and two of another
Cis-isomers- the two ligands are next to each other with a 90* bond angle
Trans-isomer- the two ligands are opposite, with a 180* angle
In what type of complexes can optical isomerism occur?
In octahedral complexes containing bidentate ligands
What are the common oxidation states of vanadium ions and their colours?
+5 yellow
+4 blue
+3 green
+2 violet
What is the complex ion found in tollens reagent. What happens when it is warmed with an aldehyde? Give the equation for this
[Ag(NH3)2]+
It is reduced
[Ag(NH3)2]+ + e- —> Ag (s) + 2NH3
What is the redox potential of an ion/atom?
A measure of how easily it is reduced to a lower oxidation’s state. The more positive the redox potential the more likely it is to be reduced, so the less stable it is
This value is the same as the standard electrode potential (as long as its is measured under standard conditions
Why will a change of ligand change the redox potential of a complex?
Because other ligands will bind more or less strongly to the central metal ion
How can pH effect the redox potential of an ion?
A change in [H+] will cause the equilibrium to shift. This increases or decreases how many electrons are accepted. This can change the redox potential/ standard electrode potential
When manganate ions are used in a titration, why is an indicator not required?
Magnate ions (MnO4-) are reduced to Mn2+ ions. The ions have different colours so a colour change can still be seen (colourless top pale pink)
What are the two types of transition metal catalysts?
Heterogeneous and homogeneous
What is a heterogeneous catalyst?
A catalyst in a different state/ phase to the reactant
Explain the three steps involved ion heterogeneous catalysts?
Adsorbtion (reactants held weakly on the surface of the catalysts to weaken the bonds)
Chemical reaction (bonds are broken, new bonds form
Desorption (leave the surface of the molecules)
How is catalyst poisoning caused in heterogeneous catalysts?
Impurities in the reactants may bind to the active sites of the catalysts. This reduces the efficiency of the catalyst as reactants cannot bind to and be catalysed
Therefore the catalysts may need replacing
How can catalyst poisoning be reduced?
By purifying the reactants
What are homogeneous catalysts?
Catalysts in the same state/phase as the reactants
How do homogeneous catalysts work?
They require an intermediate species
They catalyse reactants that repel each other (both positive or both negative ions)
The catalyst reacts with one reactant in a redox reaction
The intermediate species then reacts with the other reactant to regenerate the catalyst and product other products
What is a common example for a homogeneous catalyst, and what is the intermediate species?
Fe2+
Fe3+
Explain how carbon monoxide poison is caused in humans- using ligand substitution
What CO is inhaled, haemoglobin can substitute water ligands for CO ligands. This creates a very strong bond between Fe and CO which is not readily reversed.
Therefore oxygen cannot bind to the haemoglobin, so CO is considered toxic
What is the process of the manufacture of sulphuric acid, and what catalyst is used?
The contact process, V2O5 (heterogeneous catalyst)
Describe the process of the contact process, including the overall equations
Step 1- SO2 is held on the surface of the catalyst at the active site. The bonds are weakened and catalyst and SO2 react
V2O5 + SO —> V2O4 + SO3
Step 2- vanadium (IV) oxide reacts with oxygen to regenerate the catalyst
V2O4 + 1/2 O2 —> V2O5
Overall:
SO2 + 1/2 O2 —> SO3
What is an auto catalyst? Give an example
Where the catalyst for a reaction is a product of the reaction itself
E.g Mn2+ ions in the reaction between MnO4- and ethanedioate ions
Describe the process that happens when MnO4- ions react with ethanedioate ions
MnO4 - reacts with C2O4 2- to generate the Mn2+ catalyst. This reaction is very slow because the negative ions repel each other, so the activation energy is High
Mn2+ reacts with MnO4- to produce an intermediate species Mn3+. Faster rate because oppositely charged ions attract each other
Mn3+ reacts with C2O4 2- to regenerate Mn2+ catalyst.
Give the overall half equation for when MnO4- reacts with ethanedioate ions, state the auto catalyst and the intermediate species
2MnO4- + 5C2O4 2- + 16H+ —> 2Mn2+ + 8CO2 + 10H2O
Auto catalyst- Mn2+
Intermediate- Mn3+
What transition metal ions commonly form complexes with a linear shape?
Ag (I)
Cu(I)
Describe the colour change from when MnO42- ions are reduced top Mn2+ ions
Colourless to pale pink
