2.5 Transition Metals. Flashcards
What is a transition metal?
An element with an incomplete d-sub shell in atoms or ions. Ti → Cu
Why is zinc not a transition metal?
Zn only forms a 2+ ion which has a complete d- subshell.
4 characteristics of transition metals
• Complex formation.
• formation of coloured ions
• variable oxidation states
• catalytic activity
What is a complex?
A central metal ion surrounded by ligands.
What is a ligand?
An atom, ion or molecule which can donate a lone election pair
What is a coordinate bond?
A covalent bond in which both electrons in the shared pair come from the same atom or ion.
What is mono dentate/ multidentate/ Bidentate
Monodentate= only forming one coordinate bond per ligand
Multidentate = forming more than 2 coordinate bonds.
Bidentate = forming 2 coordinate bonds.
What is the coordination number
Number of coordinate bonds from ligands to metal ion
what are Lewis acid/bases?
Lewis acid= lone pair acceptor (metal)
Lewis base = lone pair donor (Ion)
rules of electron configuration of the transition metals
4s orbital fills before 3d
4s empties before 3d (in ions)
exceptions for the rules of electron configuration of transition metals
in chromium and copper, the 3d is filled first to provide more stability.
e.g. Cr - [Ar] 3d5 4s1, Cu - [Ar] 3d10 4s1
4 examples of common monodentate ligands
H2O, NH3, Cl- and CN-
2 examples of common bidentate ligands
1,2-diaminoethane (en)
ethanedioate (C2O4^21)
example of a common multidentate ligand and how many co-ordinate bonds does it form
EDTA^4-, forms 6 co-ordinate bonds
structure of haemoglobin
a globular protein with 4 Fe2+ centres, with a ligand taking up 4 co-ordinate sites, oxygen takes one site and haem takes the other.
what is cis-trans isomerism and when can it occur
occurs in square planar and octahedral complexes
cis = when the same ligands are next to eachother.
trans = when the same ligands are opposite eachother.
4 possible shapes of complexes + bond angles
linear, 180
square planar, 90
tetrahedral, 109.5
octahedral, 90
what is optical isomerism and when can it occur
occurs in octahedral complexes
when complexes have the mirror image to eachother
what is d orbital splitting
when a ligand causes the 5 d-orbitals to split into 3 and 2 orbitals - one set higher than the other- the difference in energy cause a high energy d-orbital and a low energy d-orbital.
how can electrons transfer between high/low energy d-orbitals
when electrons absorb light, they become excited and are promoted to a higher energy level
how do you work out the difference in energy between the high and low energy d-oritals
ΔE (J) = hv = hc/λ
h = plancks constant
v = frequency of light absorbed
c = velocity of light
λ = wavelength of light
what does ΔE depend on
- the metal ion
- the ligand
- the oxidation state
- the co-ordination number
how does visible colour arise
visible light is a mixture of colours that are not absorbed
what is UV/visible spectrometry and how does it work
a way to measure the frequency at which complexes absorb UV/visible light.
UV/visible light is passed through the complex, light which pass through are detected and those that do not, are not.
what is colorimetry
a way to measure concentration of solutions
steps of colorimetry
a calibration series of solutions with known concentrations is prepared.
a colorimeter is used to measure absorption.
a calibration curve is plotted.
a sample with an unknown concentration is measured in the calorimeter.
the absorbance is matched to the calibration curve.
why can transition metals have variable oxidation states
the energy of the different d orbital are similar, so they metal will still be stable with varied oxidation states
reduction of vanadium
vanadium is reduced by the presence of zinc in acidic solution.
vanadium is reduced from VO2 + -> VO2+ -> V3+ -> V2+.
the oxidation state going from +5 -> +2.
colour goes from yellow -> blue -> green -> violet
what is a redox titration
a titration to find out the concentration of oxidising or reducing agents
role of potassium manganate
contains MnO4- which is a common oxidising agent.
dilute sulfuric acid needs to be present in the conical flask.
potassium manganate is in the biuret and will be added until the end point, a purple solution.
what is a homogeneous and heterogeneous catalyst
homogeneous catalyst: catalyst in the same phase as the reactants
heterogeneous catalyst: catalyst in a different to the reactants
heterogenous catalysts
usually solids, occur with gaseous or aqueous reactants. the reaction will occur on the surface of the catalyst.
e.g. the haber process, the contact process
homogeneous catalysts
an intermediate species is formed, and the reaction requires a lower activation energy.
e.g. the reaction between iodide and persulfate ions
what is catalyst poisoning
when impurities bind to the surface and block active sites of the catalysts, reducing rate of reaction, making the catalyst less efficient.
strength of adsorption
the strength of adsorption helps to determine the effectiveness of the catalytic activity. having too strong adsorption means the product isnt released but having a weak adsorption means the product isnt adsorbed in a high enough concentration
why is the reaction between iodide and persulfate ions very slow
they are both negative ions, so there is a strong repulsion power which needs to be overcome in order to collide.
what is autocatalysis
when the product is the catalyst. as the reaction continues and more product is made, rate of reaction will increase.
e.g. reaction between ethanedioate and manganate ions
