Coloured Complex Ions
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What is d - orbital splitting? (whn. lgnds. bnd. cntrl. mtl. ion - d sbshl. splts. two. dff. enrgy. lvls.)
When ligands bond to a central metal ion, the d - subshell splits into two different energy levels
Why are transition metal complex ions coloured? (ctn. prt. fld. d orb. - intrct. w/ lgnds. - cse d orb. splt. + absprtn. vsble. lght.)
They contain partially filled d orbitals that interact with ligands, causing d - orbital splitting and absorption of visible light
What happens to the d orbitals when ligands attach to transition metal ion? (splt. diff. E lvls.)
Their energy increases and splits. creating an energy gap
How does d orbital splitting cause colour in transition metal ions? (elctrn.s absrb. E + prmtd. lwr/hghr. d orb. E lvl.)
Electrons absorb energy and are promoted from a lower to a higher d orbital energy level
What type of light is absorbed by transition metal complex ions? (vble. lght. w/ freq. mtches. E gap btwn. splt. d - orb.)
Visible light with a frequency that matches the energy gap between the split d orbitals
Define ground state (when all electrns. lwst. poss. E lvls.)
When all electrons are in their lowest possible energy levels
Define excited state (at lst. 1 electrn. mvd. hghr. E lvl.)
When at least one electron has moved to a higher energy level
What happens when visible light is absorbed by a transition metal complex? (elctrn. exctd. lwr E to hghr. E - d orb.)
An electron is excited from a lower energy d orbital to a higher energy d orbital
How is the energy gap related to the frequency of light absorbed? (E gp. = freq. lght. absrb.)
The energy change is directly proportional to the frequency of the light absorbed
If higher frequency (blue) light is absorbed, what does this indicate about d-orbital splitting? (lrgr. E gp btwn splt. d orb.)
A larger energy gap between the split d orbitals
If lower frequency (red) light is absorbed, what does this indicate about d-orbital splitting? (smlr. E gp. btwn. splt. d orb.)
A smaller energy gap between the split d orbitals
State the three factors that affect the colour of a transition metal complex ion (ox. ste. met. ion. - lig. typ. - coord. nmbr.)
• Oxidation state of the metal ion • Type of ligand • Coordination number
How does oxidation state affect colour? (hghr. ox. ste. - grtr. d orb. splt. - hghr. freq. lght. absrb.)
The higher the oxidation state, the greater d-orbital splitting and the higher frequency light absorbed
How does ligand type affect colour? (diff. lgnds. cse. diff. dgrs. d orb. splt.)
Different ligands cause different degrees of d-orbital splitting
State the order of increasing d-orbital splitting for these ligands: CN⁻, NH₃, H₂O, OH⁻, F⁻, Cl⁻
CN⁻ < NH₃ < H₂O < OH⁻ < F⁻ < Cl⁻
How does coordination number affect d-orbital splitting? (hghr. coord. nmbr. lds. grtr. d orb. splt.)
A higher coordination number leads to a greater d-orbital splitting
What equation links the gap in energy to frequency of light, what is the value of planck’s constant ?
△E = hv h = 6.63 x 10 to the power of negative 34 Js
What equation is used to calculate using energy change and planck’s constant?
ΔE = hc / λ
How do you convert nm to metres? How do you convert THz to Hz?
1 nm to 1 × 10⁻⁹ m 1 THz to 1 x 10¹² Hz
What is colorimetry used for? (dtrmne. conc. clrd. sol.)
To determine the concentration of a coloured solution
How does concentration affect absorbance?
Higher concentrations, mean darker colours and more light being absorbed
How is monochromatic light produced in a colorimeter? (use fltr. slct. sngle. wvlngth. lght.)
By using a filter to select a single wavelength of light
How is the concentration of an unknown solution determined using a calibration curve? (msr. absbnc. rng. knwn. conc. smple. - plt. grph. absbrnc. vs. conc. crtng. clbrtn. crve. - msrs. absbrnce. clrd. cmpls. + find. cncntrn. frm. grph.)
• Measure the absorbance of a range of known concentrations sample • Plot a graph of absorbance vs concentration, creating a calibration curve • Measure the absorbance of the coloured compelx and find concentration from graph
Why must cuvettes of the same size and material be used in colorimetry? (bcse absbrnce. dpnds, pth. lngth. + conc.)
Because absorbance depends on path length and concentration