IB Chemistry on Absorption Spectrum and Line Emission/Absorption Spectrum
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Transition metal complexes can have different colors due to the splitting of the metal ion's d orbitals caused by ligands. Ligands of varying strength cause varying degrees of d orbital splitting, represented by ΔE. Stronger ligands cause greater splitting and absorption of higher energy visible light, resulting in colors like violet or blue. Weaker ligands cause less splitting and absorption of lower energy visible light, appearing as colors like yellow or green. The spectrochemical series orders ligands from weakest to strongest field strength based on the color produced.
![Formation coloured complexes Variable Colours
Click here vanadium ion complexes Click here nickel ion complexes
V5+/ VO2
+ - yellow
V4+/ VO2+ - blue
V3+ - green
V2+ - violet
NiCI2 - Yellow
NiSO4 - Green
Ni(NO3)2 - Violet
NiS - Black
Diff oxidation states
Colour formation
Nature of
transition metal
Oxidation
state
Diff ligands Shape
Stereochemistry
Diff ligandsDiff metals
MnCI2 - Pink
MnSO4 - Red
MnO2 - Black
MnO4
- - Purple
Cr2O3 - Green
CrO4
2- - Yellow
CrO3 - Red
Cr2O7
2- - Orange
Shape/ Stereochemistry
Tetrahedral Octahedral
BlueYellow
Transition Metal – Colour Complexes
Ion Electron
configuration
Colour
Sc3+ [Ar] colourless
Ti3+ [Ar]3d1 Violet
V3+ [Ar]3d2 Green
Cr3+ [Ar]3d3 Violet
Mn2+ [Ar]3d5 Pink
Fe2+ [Ar]3d6 Green
Co2+ [Ar]3d7 Pink
Ni2+ [Ar]3d8 Green
Cu2+ [Ar]3d9 Blue
Zn2+ [Ar]3d10 colourless](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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IB Chemistry on Absorption Spectrum and Line Emission/Absorption Spectrum
- 1. Why transition metals ion complexes have diff colour? Transition Metal – Colour Complexes Colour you see is BLUE – Blue reflected/transmitted to your eyes - Red/orange absorbed (complementary colour) Colour you see is Yellow – Yellow reflected/transmitted to your eyes - Violet absorbed (complementary colour) complementary colour Blue transmitted Wave length - absorbed Wave length - absorbed Visible light Visible light Yellow transmitted absorbed
- 2. Formation coloured complexes Variable Colours Click here vanadium ion complexes Click here nickel ion complexes V5+/ VO2 + - yellow V4+/ VO2+ - blue V3+ - green V2+ - violet NiCI2 - Yellow NiSO4 - Green Ni(NO3)2 - Violet NiS - Black Diff oxidation states Colour formation Nature of transition metal Oxidation state Diff ligands Shape Stereochemistry Diff ligandsDiff metals MnCI2 - Pink MnSO4 - Red MnO2 - Black MnO4 - - Purple Cr2O3 - Green CrO4 2- - Yellow CrO3 - Red Cr2O7 2- - Orange Shape/ Stereochemistry Tetrahedral Octahedral BlueYellow Transition Metal – Colour Complexes Ion Electron configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar]3d1 Violet V3+ [Ar]3d2 Green Cr3+ [Ar]3d3 Violet Mn2+ [Ar]3d5 Pink Fe2+ [Ar]3d6 Green Co2+ [Ar]3d7 Pink Ni2+ [Ar]3d8 Green Cu2+ [Ar]3d9 Blue Zn2+ [Ar]3d10 colourless
- 3. Ion configuration Colour Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Fe2+ [Ar] 3d6 Green Co2+ [Ar] 3d7 Pink NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) Transition Metal – Colour Complexes Presence of ligand • 3d orbital split • five 3d orbital unequal in energy Mn2+ [Ar]3d5 3d yz3d xy 3d xz 3d Z 23dx 2 - y 2 ∆E lies between axes lies along axes Mn2+ :L:L :L Colour- Splitting 3d orbital by ligand :L:L :L :L :L :L :L :L :L 3d xy 3d xz 3d yz 3dx 2 - y 2 3d Z 2 No ligand – No repulsion – No splitting 3d orbitals Mn2+ No ligands approaching :L :L :L :L :L :L :L :L :L :L :L :L :L :L:L :L :L :L :L :L :L :L :L :L Ligands approaching Ligand approach not directly with 3d electron Less repulsion bet 3d with ligand Lower in energy Ligand approach directly 3d electron More repulsion bet 3d with ligand Higher in energy With ligand • Splitting of 3d orbital • 3d orbital unequal energy Elec/elec repulsion bet 3d e with ligand
- 4. Colour- Splitting of 3d orbital of metal ion by ligand NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) Splitting 3d orbital Electronic transition possible Photon light absorb to excite elec With ligand • Splitting of 3d orbital • 3d orbitals unequal energy Why Ti 3+ ion solution is violet ? violet Transition Metal – Colour Complexes Presence of ligand • 3d orbital split • five 3d orbital unequal in energy Ti3+ [Ar] 3d1 3d yz3d xy 3d xz 3d Z 23d x 2 - y 2 Ti3+ [Ar] 3d1 ∆E Ion configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Fe2+ [Ar] 3d6 Green Co2+ [Ar] 3d7 Pink Ni2+ [Ar] 3d8 Green Cu2+ [Ar] 3d9 Blue Zn2+ [Ar] 3d10 colourless Green / yellow wavelength - Abosrb to excite electron О
- 5. Colour- Splitting of 3d orbital of metal ion by ligand NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) Splitting 3d orbital Electronic transition possible Photon light absorb to excite elec With ligand • Splitting of 3d orbital • 3d orbitals unequal energy Why Cu3+ion solution is blue ? Blue Transition Metal – Colour Complexes Presence of ligand • 3d orbital split • five 3d orbital unequal in energy Cu2+ [Ar] 3d9 3d yz3d xy 3d xz 3d Z 23d x 2 - y 2 Cu2+ [Ar] 3d9 ∆E Ion configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Fe2+ [Ar] 3d6 Green Co2+ [Ar] 3d7 Pink Ni2+ [Ar] 3d8 Green Cu2+ [Ar] 3d9 Blue Zn2+ [Ar] 3d10 colourless Red / orange wavelength - Abosrb to excite electron О Cu2+
- 6. Colour- Splitting of 3d orbital of metal ion by ligand NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) Splitting 3d orbital NO electron NO absorption light NO electronic transition possible With ligand • Splitting of 3d orbital • 3d orbital unequal energy Why Sc 3+ ion solution is colourless? Colourless Transition Metal – Colour Complexes Presence of ligand • 3d orbital split • five 3d orbital unequal in energy Sc3+ [Ar] 3d0 3d yz3d xy 3d xz 3d Z 23d x 2 - y 2 Sc3+ [Ar] 3d0 ∆E Ion configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Fe2+ [Ar] 3d6 Green Co2+ [Ar] 3d7 Pink Ni2+ [Ar] 3d8 Green Cu2+ [Ar] 3d9 Blue Zn2+ [Ar] 3d10 colourless All wavelength transmitted Sc3+ NO absorption white
- 7. Colour- Splitting of 3d orbital of metal ion by ligand NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) With ligand • Splitting of 3d orbital • 3d orbital unequal energy Why Zn 3+ ion solution is colourless? Colourless Transition Metal – Colour Complexes Presence of ligand • 3d orbital split • five 3d orbital unequal in energy Zn2+ [Ar] 3d10 3d yz3d xy 3d xz 3d Z 23d x 2 - y 2 Zn2+ [Ar] 3d10 ∆E Ion configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Fe2+ [Ar] 3d6 Green Co2+ [Ar] 3d7 Pink Ni2+ [Ar] 3d8 Green Cu2+ [Ar] 3d9 Blue Zn2+ [Ar] 3d10 colourless Zn2+ All wavelength transmittedSplitting 3d orbital FULLY FILLED NO absorption light NO electronic transition possible NO absorption white
- 8. Colour- Splitting of 3d orbital of metal ion by ligand NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) With ligand • Splitting of 3d orbital • 3d orbital unequal energy Why Cu+ ion solution is colourless? Colourless Transition Metal – Colour Complexes Presence of ligand • 3d orbital split • five 3d orbital unequal in energy Cu+ [Ar] 3d10 3d yz3d xy 3d xz 3d Z 23d x 2 - y 2 Cu+ [Ar] 3d10 ∆E Cu+ All wavelength transmittedSplitting 3d orbital FULLY FILLED NO absorption light NO electronic transition possible Ion configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Cu+ [Ar] 3d10 Colourless Cu2+ [Ar] 3d9 Blue white NO absorption
- 9. Colour- Splitting of 3d orbital of metal ion by ligand NO ligand • Degenerate • 3d orbital same energy level • five 3d orbital equal in energy Five 3d orbital (Degenerate – same energy level) No ligand/Water • NO Splitting 3d orbital • 3d orbital equal energy Why Cu3+ion anhydrous is colourless ? Transition Metal – Colour Complexes NO ligand • 3d orbital split • five 3d orbital equal in energy Cu2+ [Ar] 3d9 3d yz3d xy 3d xz 3d Z 23d x 2 - y 2 Cu2+ [Ar] 3d9 Ion configuration Colour Sc3+ [Ar] colourless Ti3+ [Ar] 3d1 Violet V3+ [Ar] 3d2 Green Cr3+ [Ar] 3d3 Violet Mn2+ [Ar] 3d5 Pink Fe2+ [Ar] 3d6 Green Co2+ [Ar] 3d7 Pink Ni2+ [Ar] 3d8 Green Cu2+ [Ar] 3d9 Blue Cu2+ Colourless NO Splitting 3d orbital NO absorption light NO electronic transition possible All wavelength transmit white NO absorption
- 10. Formation coloured complexes V5+/ VO2 + - yellow V4+/ VO2+ - blue V3+ - green V2+ - violet NiCI2 - Yellow NiSO4 - Green Ni(NO3)2 - Violet NiS - Black Diff oxidation states Colour formation Nature of transition metal Diff ligands Diff metals MnCI2 - Pink MnSO4 - Red MnO2 - Black MnO4 - - Purple Cr2O3 - Green CrO4 2- - Yellow CrO3 - Red Cr2O7 2- - Orange Shape/ Stereochemistry Tetrahedral Octahedral BlueYellow TransitionMetal – Colour Complexes Ion configuration Colour Ti3+ [Ar]3d1 Violet V3+ [Ar]3d2 Green Cr3+ [Ar]3d3 Violet Mn2+ [Ar]3d5 Pink Fe2+ [Ar]3d6 Green Co2+ [Ar]3d7 Pink Ni2+ [Ar]3d8 Green Cu2+ [Ar]3d9 Blue Colour- Splitting3d orbital by ligand Strong ligand (highercharge density) ↓ Greatersplitting ↓ Diff colour Weak ligand (Low charge density) ↓ Smallersplitting ↓ Diff colour No ligand ↓ No splitting ↓ No colour Spectrochemical series – Strong ligand → Weak Ligand Co/CN > en > NH3 > SCN- > H2O > C2O4 2- > OH- > F- > CI- > Br- > I- NO ligand – NO splitting 3d orbital (Same energy level) WEAK ligand – small splitting 3d orbital (Unequal energy) ∆E ∆E STRONG ligand – greater splitting 3d orbital (Unequal energy)
- 11. I- < Br- < CI- < F- < OH- < C2O4 2- < H2O < SCN- < NH3 < en < Co/CN Transition Metal – Colour Complexes Colour- Splitting3d orbital by ligand Strongligand (higherchargedensity) ↓ Greatersplitting - ↑∆E Diff colour Weak ligand (Low chargedensity) ↓ Smallersplitting - ↓∆ E Diff colour No ligand ↓ No splitting No colour Spectrochemical series – Weak ligand → Strong Ligand NO ligand – NO splitting 3d orbital (Same energy level) WEAK ligand – small splitting 3d orbital (Unequal energy) ∆E ∆E STRONG ligand – greater splitting 3d orbital (Unequal energy) Very Strongligand ↓ Greatersplitting - ↑∆E Diff colour ∆E Ion ES Colour Cu(CI4)2- 3d9 Colourless Cu(CI4)2- 3d9 Green Cu(H2O)6 2+ 3d9 Blue Cu(NH3)4 2+ 3d9 Violet Cu2+ [Ar] 3d9 STRONGEST ligand – greatest splitting О О О Ligand I- Br- CI- F- C2O4 2- H2O SCN- NH3 en Co/CN- ʎ (wave length) longest shortest ∆E Weak field Smallest Split Strong field Highest Split [Cu(CI)4]2- [Cu(NH3)4]2+[Cu(H2O)6]2+ О О О
- 12. H2O stronger ligand ↓ Greater spitting ∆E ↓ Higher energy wavelength absorbed CI- weak ligand ↓ Small spitting ∆E ↓ Low energy wavelength absorbed NH3 strongest ligand ↓ Greatest spitting ∆E ↓ Highest energy wavelength absorbed - Higher energy absorbed - Orange wavelength absorb to excite electron - Highest energy absorbed - Yellow wavelength absorb to excite electron TransitionMetal – Colour Complexes Colour- Splitting3d orbital by ligand Strongligand (highercharge density) ↓ Greatersplitting - ↑∆E - Diff colour Weak ligand (Low charge density) ↓ Smallersplitting - ↓∆ E - Diff colour Spectrochemical series – Weak ligand → Strong Ligand WEAK ligand – small splitting 3d orbital (Unequal energy) ∆E ∆E STRONG ligand – greater splitting 3d orbital (Unequal energy) Very Strong ligand ↓ Greatersplitting - ↑∆E- Diff colour ∆E Cu(H2O)6 2+ 3d9 Blue STRONGEST ligand – greatest splitting [Cu(NH3)4]2+[Cu(H2O)6]2+ - Lower energy absorbed - Red wavelength absorb to excite electron [Cu(CI)4]2- Cu(CI4)2- 3d9 Green Cu(NH3)4 2+ 3d9 Violet
- 13. Nuclear charge - +5 ↓ Strong ESF atrraction bet –ve ligand ↓ Greatest splitting ∆E ↓ Highest energy wavelength absorb Nuclear charge - +3 ↓ Strong ESF atrraction bet –ve ligand ↓ Greater splitting ∆E ↓ Higher energy wavelength absorb Mn(H2O)6 2+ +2 PINK Nuclear charge - +2 ↓ Weak ESF atrraction bet –ve ligand ↓ Smaller splitting ∆E ↓ Low energy wavelength absorb - Higher energy absorbed - Blue wavelength absorb to excite electron - Highest energy absorbed - Violet wavelength absorb to excite electron TransitionMetal – Colour Complexes Colour- Splitting3d orbital by ligand High nuclearcharge / charge density ↓ Greatersplitting - ↑∆E - Diff colour Low nuclearcharge /charge density ↓ Smallersplitting - ↓∆ E - Diff colour Nuclearcharge on metalion Low nuclear charge – small splitting 3d orbital (Unequal energy) ∆E ∆E High nuclear charge – greater splitting 3d orbital (Unequal energy) Highest nuclearcharge/charge density ↓ Greatest splitting - ↑∆E- Diff colour ∆E Fe(H2O)6 3+ +3 YELLOW HIGHEST nuclear charge – greatest splitting Fe(H2O)6 3+ - Lower energy absorbed - Green wavelength absorb to excite electron V(H2O)6 5+ +5 YELLOW/GREEN Mn(H2O)6 2+ V(H2O)6 5+
- 14. Oxidation number - +3 ↓ Strong ESF atrraction bet –ve ligand ↓ Greater splitting ∆E ↓ Higher energy wavelength absorb Oxidation number - +2 ↓ Weak ESF atrraction bet –ve ligand ↓ Smaller splitting ∆E ↓ Low energy wavelength absorb TransitionMetal – Colour Complexes Colour- Splitting3d orbital by ligand Higheroxidation number/charge density ↓ Greatersplitting - ↑∆E - Diff colour Lower ESF attraction – small splitting 3d orbital (Unequal energy) ∆E ∆E STRONG ligand – greater splitting 3d orbital (Unequal energy) ∆E Fe(H2O)6 3+ +3 Yellow - Lower energy absorbed - Red wavelength absorb to excite electron Fe(H2O)6 2+ +2 Green Oxidation numberon metal ion Low oxidation number/charge density ↓ Smallersplitting- ↓∆ E - Diffcolour Fe(H2O)6 2+ - Higher energy absorbed - Blue wavelength absorb to excite electron Fe(H2O)6 3+ V(H2O)6 5+ +5 YELLOW/GREEN Highest oxidation number/charge density ↓ Greatest splitting - ↑∆E- Diff colour HIGHEST nuclear charge – greatest splitting - Highest energy absorbed - Violet wavelength absorbed to excite electron Nuclear charge - +5 ↓ Strongest ESF atrraction bet –ve ligand ↓ Greatest splitting ∆E ↓ Highest energy wavelength absorb V(H2O)6 5+
- 15. ElectromagneticSpectrum Electromagneticspectrumranges fromRadiowavesto Gamma waves. - Form of energy - Shorterwavelength-> Higherfrequency-> Higherenergy - Longerwavelength-> Lower frequency-> Lower energy Electromagneticradiation • Travel at speedof light, c = fλ -> 3.0 x 108 m/s • Light Particle – photonhave energygivenby -> E = hf • Energyphoton - proportionalto frequency Inverse relationship between- λ and f Wavelength, λ - long Frequency, f - low Wavelength, λ - short Frequency, f - high Plank constant • proportionality constant bet energy and freq Excellent video wave propagation Click here to view.
- 16. Click here to view video ElectromagneticWave propagation. Wave Electromagneticradiation Electromagnetic radiation • Moving charges/particlesthrough space • Oscillating wave like property of electric and magnetic field • Electric and magnetic field oscillateperpendicularto each other and perpendicularto direction of wave propagation. Electromagneticwave propagation Wave – wavelength and frequency - travel at speed of light Violet λ = 410nm Red f = c/λ = 3 x 108/410 x 10-9 = 7.31 x 1014 Hz E = hf = 6.626 x 10-34 x 7.31 x 1014 = 4.84 x 10-19 J λ = 700nm f = c/λ = 3 x 108/700 x 10-9 = 4.28 x 1014 Hz E = hf = 6.626 x 10-34 x 4.28 x 1014 = 2.83 x 10-19 J
- 17. Light given off Continuous Spectrum : Light spectrum with all wavelength/frequency Emission Line Spectrum : • Spectrum with discrete wavelength/ frequency • Emitted when excited electrons drop from higher to lower energy level Absorption Line Spectrum : • Spectrum with discrete wavelength/frequency • Absorbed when ground state electrons are excited Atomic Emission Vs Atomic Absorption Spectroscopy Ground state Excited state Electrons from excited state Emit radiation when drop to ground state Radiation emitted Emission Spectrum Electrons from ground state Absorb radiation to excited state Electrons in excited state Radiation absorbed ContinuousSpectrumVs Line Spectrum Light/photon ABSORB by electron
- 18. Range Light/photon ABSORB by electron Light/photon ABSORB by electron Absorptionspectrum is broad/continuous Ions in solution(Sovent) 2 ∞ Absorption spectrum for ions in solution ↓ Surrounded by ligand and solvent ↓ Have electronic excitation transitionstate + vibrational/rotationalenergy level ↓ Continuous broad spectrum Gaseous state – only gaseous ion present ↓ Complete vacuum ↓ Well defined spectralline exist ↓ Either excited or not ↓ Only electronic transition state allowed 1 2 3 4 5 Light given off Absorption/Emission spectrum -discrete/fixed/line Gaseous ions (Vacuum) Vs Electronic ground state Electronic excited state Line emission spectrum Line absorption spectrum Electronic ground state 1 Electronic excited state 3 Vibrational energy level Rotational energy level Whole range of wavelength/broadspectrum can be absorbed to excite electron to electronic/vibrational/rotationallevel
- 19. Absorptionspectrum is broad/continuous Ions in solution(Solvent) 2 No line emission spectrum seen as electron drop to lower level ↓ Energy is lost in small steps to solvent/environment Electronic ground state 1 Electronic excited state 3 Vibrational energy level Rotational energy level Whole range of wavelength/broadspectrum can be absorbed to excite electron to electronic/vibrational/ rotationallevel Absorption spectrum for ions in solution ↓ Surrounded by ligand and solvent ↓ Have electronic excitation transitionstate + vibrational/rotationalenergy level ↓ Continuous broad spectrum Absorptionspectrum is broad/continuous Ions in solution(Solvent) Whole range of wavelength/broadspectrum can be absorbed to excite electron to electronic/vibrational/rotationallevel Electronic ground state 1 2 3 Range Light/photon ABSORB by electron Electronic excited state Vibrational energy level Rotational energy level Energy lost in small steps Absorbed by solvent Lost to environment