Inorganic Chapter 4: Transition Metals Flashcards
Where are transition metals found in the periodic table?
The d-block
What causes the special chemical properties of transition metals?
The partially filled d-block
What 2 metals in period 4 aren’t transition metals?
Sc and Zn - Scandium forms an ion with an empty d sub-level, while Zinc forms an ion with a full d sub-level.
Which electrons are lost first when you have a full 4s orbital and a partially filled 3d orbital?
The s orbitals go first, then the d orbitals.
What physical properties do transition metals generally share?
High density
High melting/boiling points
Similar ionic radius
What are the four main special properties of transition metals?
Can form complex ions
Can form coloured ions
Good catalysts
Can exist in variable oxidation states
What is a complex ion?
A metal ion surrounded by ligands
What is a ligand?
An atom or molecule that donates a pair of electons to a central transition metal ion, forming a co-ordinate bond.
What is the coordination number?
The numer of coordinate bonds formed with the central metal ion.
What shape is formed when a complex ion has 6 coordinate bonds?
Octahedral
What shape is formed when a complex ion has 4 coordinate bonds?
Tetrahedral or Square planar - Square Planar is the exception, only occurs sometimes e.g. Cisplatin
What complex ions form linear shapes?
Silver-based complexes e.g. [Ag(NH3)2]+
What are small ligands that can form 6 coordinate bonds on an ion?
H2O, NH3
What are some larger ligands that can only form 4 coordinate bonds on an ion?
Cl-
What does the overall charge on a complex represent?
Its total oxidation state
How can you work out the oxidation state of the central metal ion in a complex?
Total oxidation state - oxidation states of all the ligands
Why does a ligand need to have at least 1 lone pair?
Otherwise it has nothing to donate
What is meant by a monodentate ligand?
The ligand can only form 1 coordinate bond - only has 1 lone pair
What is meant by a multidentate ligand?
The ligand can form more than 2 coordinate bonds - has more than 2 lone pairs
What is a Bidentate ligand?
A ligand that has 2 lone pairs - can form 2 coordinate bonds
What is an example of a naturally-occuring complex ion?
Haemoglobin
Why does Carbon monoxide cause oxygen poisoning?
Oxygen binds to the haemoglobin as a lingand, but CO does too, and it’s a strong ligand, so won’t get displaced by oxygen molecules on the haemoglobin.
What type of isomerism can complex ions show?
Optical isomerism
Cis-Trans Isomerism
How do octahedral complexes show Cis-Trans isomerism?
The Trans version has the two odd ligands opposite each other, while the Cis version has them next to each other.
How do different coloured ions form?
The 3d sub-level is split into two energy levels when ligands bond to a central ion. There is an energy gap between the lower and upper levels, and the energy needed to promote an electron to the higher level comes from visible light, thereby determining which light wavelengths are absorbed.
What formula is used to calculate the energy gap?
ΔE = hv = hc/λ
v = frequency of light absorbed (hz)
h = planck’s constant (J/s)
c = speed of light (m/s)
λ = wavelength of light absorbed (m)
What is the use of coloured ions?
You can identify ions via their colours
What are the three factors that affect the colour of an ion?
Oxidation state
Coordination number
Changes in ligand
How can you use spectroscopy to determine concentration of transition metal ions?
White light is shone through a filter, which is chosen to only let through the colour of light absorbed by the sample. This light then passes to a colorimeter, which calculates how much light was absorbed by the sample. This measurement can then be used to calculate concentration using a calibration curve.
How do you make a calibration curve?
Plot a graph of relative absorbance of an ion against concentration of the ion, using absorbtion data from known concentrations.
What is ligand substitution?
When 1 ligand swaps places with another in a complex.
What changes occur in the complex after a ligand substitution?
Colour change
If the ligands are a similar size, the coordination number and shape will not change.
If the ligands are different sizes, there will be a change in coordination number & shape.
Under what condition can ligand substitutions not be reversed?
If the newly formed complex ion is much more stable than the old one.
What can cause a complex ion to be more or less stable?
Multidentate ligands tend to form more stable complexes than monodentate ligands
If the new ligands form stronger bonds with the central ion, they will create a more stable complex.
What is the chelate effect?
The effect which causes multidentate ligands to form more stable complexes than monodentate ligands. There are more particles when monondentate ligands are substituted for bidentate or multidentate ligands, so entropy will increase, thereby increasing stability.
What is special about the oxidation states of transition metals?
They’re variable - can exist in different states
What reaction takes place when you switch between oxidation states?
A redox reaction
What is redox potential?
It tells you how easily an ion or atom is reduced to a lower oxidation state.
What can redox potential also be shown as?
Standard Electrode Potential
What can make it so that redox potential isn’t always the same as standard electrode potential?
Different ligands in the solution can have different effects depending on how they bond with the metal
pH of the solution affects the size of the redox potential
Generally, more acidic = larger redox potential and vice versa
Why does Tollen’s reagent form a silver mirror?
It contains a silver complex that is reduced to elemental silver - forms the ‘silver mirror’
What type of titration is undertaken when you use transition metal ions?
Redox titrations - colour change is the end point
How do transition metal catalysts work?
They can change oxidation states - they can be reduced/oxidised at the start of the reaction, and then get oxidised/reduced at the end to come out unaffected.
What does it mean if a catalyst is homogenous?
It is in the same state as the reactants
What does it mean if a catalyst is heteregenous?
It is in a different state from the reactants
What are some examples of heterogenous catalysts?
Iron in the Haber Process - makes ammonia
Vanadium Oxide in the contact process - makes Sulfuric acid
What is catalyst poisoning?
When impurities in the reaction mixture bind to the catalyst’s surface and block reactants from being absorbed.
What is different about a homogenous catalyst & how it speeds up a reaction?
The reaction takes place through an intermediate species - this is why the graph has 2 humps
What is an example of a transition metal with 4 oxidation states?
Vanadium (V)
How can you reduce vanadium ions?
Add zinc in an acidic solution
What is Autocatalysis?
When a product catalyses the reaction. This means that as the reaction progresses, the reaction will speed up.
What is a metal-aqua complex ion?
A complex formed when transition metal compounds dissolve in water.
Are solutions containing metal-aqua complexes typically alkaline or acidic?
Acidic - more acidic the greater the charge is
Why are metal-aqua ion solutions more acidic with greater charge?
Because 3+ ions are more polarising than 2+ ions, so therefore it’s more likely hydrogen will be released.
How can you form precipitates from solutions of metal-aqua ions?
Add OH- ions - shifts the equilbrium to the right by removing H3O+ ions, eventually leaving an insoluble metal hydroxide with 3 OH ligands and 3 H2O ligands.
What is an example of a metal hydroxide that is amphoteric?
Aluminium Hydroxide
What effects can adding ammonia have on a metal-aqua complex solution?
It creates an equilbibrium to produce OH ions.
Excess ammonia can dissolve precipitates.
What is the result of a metal-aqua complex reaction with sodium hydroxide?
All four metal aqua ions will form precipitates, but only aluminium hydroxide precipitate will dissolve in excess sodium hydroxide.
What is the result of a metal-aqua complex reaction with Ammonia?
All four complexes will form ppts with ammonia, but only copper hydroxide will dissolve in excess.
What is the result of a metal-aqua complex reaction with sodium carbonate?
All 4 metal complexes will form ppts in sodium carbonate, but only Aluminium or Iron complexes will bubble. Fe3+ will give off a gas, while Fe2+ will not.
What colour is the copper metal-aqua ion?
Blue solution
What colour is the Iron 2+ metal-aqua ion?
Green solution
What colour is the Aluminium metal-aqua ion?
Colourless solution
What colour is the Iron 3+ metal-aqua ion?
Yellow solution
What colour is the copper metal-aqua ion in OH- or NH3?
Blue precipitate
What colour is the Iron 2+ metal-aqua ion in OH- or NH3?
Green precipitate
What colour is the Aluminium metal-aqua ion in OH- or NH3?
White precipitate
What colour is the Iron 3+ metal-aqua ion in OH- or NH3?
Brown Precipitate
What colour is the Aluminium metal-aqua ion in excess OH-?
Colourless solution - ppt dissolves.
Other 3 - no change.
What colour is the copper metal-aqua ion in excess ammonia?
Deep blue solution - ppt dissolves
Other 3 - no change
What colour is the copper metal-aqua ion with Na2CO?
Forms a green-blue ppt
What colour is the Iron 2+ metal-aqua ion with Na2CO?
Forms a green ppt
What colour is the Aluminium metal-aqua ion with Na2CO?
Forms a white ppt
What colour is the Iron 3+ metal-aqua ion with Na2CO?
Forms a brown ppt
