Chapter 23 - Transition Metals Flashcards
Why do transition metals behave so differently to group 1 and 2 metals?
Transition metals have access to incomplete d orbitals
What do the properties of transition metals include?
Coloured ions
Variable oxidation states
Ability to form complexes
Catalytic activity
What is a ligand?
A ligand is a molecule or ion capable of forming a dative bond with a transition metal by donating 2 electrons
What is a complex?
A complex is a central transition metal ion or atom with dative bonds to ligands
What is the co-ordination number of a complex?
The co-ordination number is the number of dative bonds present in a complex
What are monodentate ligands?
Ligands which can only form one dative bond with a transition metal
What are three examples of monodentate ligands?
Ammonia (NH3)
Water (H2O)
Cl-
What can the monodentate ligands H20 and NH3 do due to their properties?
Out of the three common monodentate ligands, ammonia and water are fairly similar due to their same and neutral charge, therefore they can easily be substitued without changing co-ordination number of charge of the complex. This substitution can be complete or incomplete (all ligands or substituted or only some of them)
What happens if ammonia or water is substituted by chloride ion
Usually, the chloride ion ligands will result in lower co-ordination numbers due to its increased size and charge
What are bidentate ligands? Give two examples
Bidentate ligands are able to form 2 dative bonds with the central transition metal.
Ethylenediamine (H2NCH3CH3NH2)
Ethanedioate (C2O4-)
What is a multidentate ligand? Give one example
Ligand capable of forming more than 2 dative bonds.
EDTA(4-) is capable of forming 6 dative bonds
What is haem?
A Fe2+ compex with a multidentate ligand
Why does the structure of haem make carbon monoxide so dangerous for humans?
Because carbon monoxide is capable of performing ligand substitution with oxygen and therefore oxygen cannot be transported
What is the chelate effect and why does it occur?
Multidentate will replace bidentate ligands and bidentate replace monodentate ligands. They do this because it is entropically favourable as one bidentate takes the place of 2 monodentate, increasing the number of particles in solution
What shape is often formed by complexes with H2O and NH3 ligands?
Octahedral
What type of isomerism do octahedral complexes with monodentate ligands form?
cis-trans isomerism
What type of isomerism do octahedral complexes with bidentate ligands form?
Optical isomerism
What shape do Cl- ligands typically form? What shape can also be formed and what can it express?
Tetrahedral, however square planar can sometimes form and they express cis-trans isomerism, e.g cisplatin
What linear complex is commonly used as a reagent?
Tollen’s reagent, a complex of silver with 2 ammonia ligands
Why do ions form coloured solutions?
When visible light is absorbed by electrons and used to promote them into higher d orbitals, the energy is therefore absorbed by the ion and the other wavelengths are transmitted, forming a coloured solution
How can you calculate the energy difference between ground state and excited electrons?
DeltaE (change in energy) = hv = hc/lambda
What leads to a change in colour of an ion?
Change in oxidation state, ligand type or co-ordination number will all change DeltaE and therefore colour of ion
How can coloured ions be used by chemists?
It can be used in spectroscopy, with simple colourimetry being able to determine concentration of coloured ions in solution
Which transition metal can be reduced by zinc in acidic solution from its 5+ ion, what states is it changed to?
Vandate (V) ions are reduced to vanadium (IV), (III) and (II) ions
Which two factors affect the ability of transition metal ions to go from a higher to lower oxidation state?
pH and type of ligand
Which pH conditions favour which oxidation states?
Alkaline - oxidation
Acidic - reduction
What is a heterogenous catalyst?
A catalyst in a different state as the reactants, and functions by adsorbing the reactants to its surface, pressuring the bonds allowing them to break more easily. An example of this is a catalytic converter
What is a support medium for heterogenous catalysts?
It is a surface which the catalyst can be added to, to maximise surface area and therefore increase effectiveness, such as the ceramic honeycomb lattice in catalytic converters
What can reduce efficiency of heterogenous catalysts?
They can become “poisoned” by impurities which block the active sites of the catalysts and don’t unbind
What is the catalyst used in the Contact process, give the reactions it is used in
V2O5, acting as a heterogenous catalyst
SO2 + V2O5 -> V2O4 + SO3(useful product - used to make sulfuric acid)
2V2O4 + O2 -> 2V2O5 (catalyst regenerated)
Which catalyst is used in the Haber process?
Iron
What is a homogenous catalyst, and how do they work?
A homogenous catalyst is a catalyst in the same state as the reactants, and instead reacts with the reactants to form an intermediate process which is energetically favourable
Which catalyst is used in the reaction between Iodide ions and peroxdisulfate ions, give equations
Iron(II)
S2O8 2- + 2Fe 2+ -> 2SO4 2- + 2Fe 3+
2Fe 3+ + 2I - -> 2Fe 2+ + I2
What is autocatalysis?
Where a product is able to catalyse the reactants of the reaction
Give an example of an autocatalysed reaction. Give the non catalysed reaction and the two catalysed reactions
The reaction between ethanedioate and potassium manganate, because the Mn2+ ions released in the reaction will catalyse the reactions
2MnO4(-) + 16 H+ + 5C2O4 (-) -> 2Mn(2+) + 8H2O + 10CO2
4Mn(2+) + MnO4(-) + 8H+ -> 5Mn(3+) + 4H2O
2Mn(3+) + C2O4(-) -> 2CO2 + 2Mn(2+)
