Transition Metals - d-orbital splitting & the other physics part Flashcards
how does a d-sub shell split
it splits into 2 when 2 ligands bonds with the central ion. this causes some orbitals to gain energy and an energy gap (Delta) /\ E is created.
what are the two energy levels that the d-orbital splits into
ground state energy - lowest energy level
and the exited state - highest energy level.
what results in the exitation of the elceltrons from ground state to exited state.
visible light energy exites energy in the lower orbitals into the higher levels.
what is essential for the exitation of electrons to happen
the enrgy from the light must equal the enrgy gap /\E
how does colour arise
colour arises from electronic transitions from the ground state to exited state: between different d orbitals.
a portion of visible light is absorbed to promote d electrson to higher energy levels. the light that isnt absorbed is transmitted to give the substance colour.
what factors influence the size of the /\E
- the coordination number
- ligand
- oxidation state of the central metal ion
what effect does changing the coordination number, ligand and oxidation state have on colour
altering those factors alters the enegy split between the d-orbitals, this changes the /\E and hence changes the frequency of light absorbed.
what happens to the frequencies of light that are transmitted or reflected away from some complexes.
the combination of all these frequencies create a complementary colour that is observed.
what does a larger /\E gap mean
a higher frequency of light absorbed.
why is scandium colourless
its ion Sc3+ has no d-electrons left to migrate to a higher energy level, so no energy transfer equal to that of visible light. so it appears colourless.
why is zinc colourless
it’s ion is Zn2+ with a full d-orbital, with no space for electrons to migrate to a higher energy level, no energy transfer equal to that of visible light, so appears colourless.
state what reaction is happening and the factors influencing the colour change in this reaction =
[Co(H2O)6]2+ + 4Cl- -> [CoCl4]2- + 6H2O
Pink -> Blue
octaheadral -> tetraheadral.
Ligand Substituton Reaction - larger uncharged H2O ligand substituted by smaller, chanrged Cl-
factors =
1. ligand
2. coordination number
whats the equation that links colour, wavelength and frequency of the light abdprbed with the energy difference. (units and all that on paper flashcard)
/\E (energy differecne between split d-orbitals) = hv = hc/wavelength of light absorbed.
what is the absorbance of light used in ?
it is used in spectrometry to determine the concentration of coloured ions.
what is a blank sample
the solvent your using to dissolve the transition metal ion. normally just water.
what is the first step when doing calorimetry.
the calorimeter must be calibrated - set to zero. to do this we mesaure the absorbance of a blank sample
what does calorimetry/spectrometry
it mesaures the absorbance of light by a coloured sample. the more concentrated the sample is the darker it’s colour and hence more light absorbed.
what is the second step when doing calorimetry
white light is filtered into a narrow range of frequencies. and monochromatic light - single colour light is produced.
why must the choice of filter be done carfeully
the choice of filter is important cos the colour produced from the filter must be absorbed by the metal ion solution.
what is the third step in calorimetry and what is a cuvette
the monochromatic light passes through a sample and some of the light is absorbed. the sample is held in a vessel called a cuvette. the cuvette basically has 2 frosted sides and 2 colourless sides. when the light is being shone through it, it must makse sure it passes through the frosted side. this is cos oils from fingerprints can influence the colour.
what is the final step in calorimetry.
the light that isnt absorbed by the sample, travels to the detector. the detector mesuares the level of absorbance by comapring it to the absorbance in the blank sample.
how is a calibration curve made
created by making up a range of known different concentrations of the transition metal ion slolution. the absorbance of each one is mesaured and the results are plotted.
the absorbance on the y-axis and the range of known concentrations of ion on the x-axis.
how are the different samples for the calibration curve made.
they are made by diluting different concentrations of the metal ions. the metal ions and solvent used in the sample being tested should be the same as the ones used for the cuvre. and a pippete is used to ensure xaccurate volumes are used.
what do you need to know to be able to find the concetration of the metal ion
the absorbance of it, so the concetration can be identified on the calibration curve.
