IB Chemistry on Absorption Spectrum and Line Emission/Absorption Spectrum
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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
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 ligands Diff metals
MnCI2 - Pink MnSO4 - Red MnO2 - Black MnO4
- - Purple
Cr2O3 - Green CrO4
2- - Yellow
CrO3 - Red
Cr2O72-
- Orange
Shape/ Stereochemistry
Tetrahedral Octahedral
Blue Yellow
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
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 yz 3d xy 3d xz 3d Z2 3dx
2 - y2
∆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 3dx2 - y
2 3d Z2
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
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 yz 3d xy 3d xz 3d Z2 3d x
2 - y2
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
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 yz 3d xy 3d xz 3d Z2 3d x
2 - y2
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+
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 yz 3d xy 3d xz 3d Z2 3d x
2 - y2
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
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 yz 3d xy 3d xz 3d Z2 3d x
2 - y2
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 transmitted Splitting 3d orbital
FULLY FILLED
NO absorption light
NO electronic transition possible
NO absorption
white
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 yz 3d xy 3d xz 3d Z2 3d x
2 - y2
Cu+ [Ar] 3d10 ∆E
Cu+
All wavelength transmitted Splitting 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
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 yz 3d xy 3d xz 3d Z2 3d x
2 - y2
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
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
Cr2O72-
- Orange
Shape/ Stereochemistry
Tetrahedral Octahedral
Blue Yellow
Transition Metal – 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- Splitting 3d orbital by ligand
Strong ligand (higher charge density) ↓
Greater splitting ↓
Diff colour
Weak ligand (Low charge density) ↓
Smaller splitting ↓
Diff colour
No ligand ↓
No splitting ↓
No colour
Spectrochemical series – Strong ligand → Weak Ligand
Co/CN > en > NH3 > SCN- > H2O > C2O42- > 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)
I- < Br- < CI- < F- < OH- < C2O42- < H2O < SCN- < NH3 < en < Co/CN
Transition Metal – Colour Complexes Colour- Splitting 3d orbital by ligand
Strong ligand (higher charge density) ↓
Greater splitting - ↑∆E Diff colour
Weak ligand (Low charge density) ↓
Smaller splitting - ↓∆ 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 Strong ligand ↓
Greater splitting - ↑∆E Diff colour
∆E
Ion ES Colour
Cu(CI4)2- 3d9 Colourless
Cu(CI4)2- 3d9 Green
Cu(H2O)62+ 3d9 Blue
Cu(NH3)42+ 3d9 Violet
Cu2+ [Ar] 3d9 STRONGEST ligand – greatest splitting
О
О
О
Ligand I- Br- CI- F- C2O42- 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
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
Transition Metal – Colour Complexes Colour- Splitting 3d orbital by ligand
Strong ligand (higher charge density) ↓
Greater splitting - ↑∆E - Diff colour
Weak ligand (Low charge density) ↓
Smaller splitting - ↓∆ 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 ↓
Greater splitting - ↑∆E- Diff colour
∆E
Cu(H2O)62+ 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)42+ 3d9 Violet
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)62+ +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
Transition Metal – Colour Complexes Colour- Splitting 3d orbital by ligand
High nuclear charge / charge density ↓
Greater splitting - ↑∆E - Diff colour
Low nuclear charge /charge density ↓
Smaller splitting - ↓∆ E - Diff colour
Nuclear charge on metal ion
Low nuclear charge – small splitting
3d orbital (Unequal energy)
∆E ∆E
High nuclear charge – greater splitting
3d orbital (Unequal energy)
Highest nuclear charge/charge density ↓
Greatest splitting - ↑∆E- Diff colour
∆E
Fe(H2O)63+ +3 YELLOW
HIGHEST nuclear charge – greatest splitting
Fe(H2O)63+
- Lower energy absorbed
- Green wavelength absorb to excite electron
V(H2O)65+ +5 YELLOW/GREEN
Mn(H2O)62+ V(H2O)6
5+
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
Transition Metal – Colour Complexes Colour- Splitting 3d orbital by ligand
Higher oxidation number/charge density ↓
Greater splitting - ↑∆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)63+ +3 Yellow
- Lower energy absorbed
- Red wavelength absorb to excite electron
Fe(H2O)62+ +2 Green
Oxidation number on metal ion
Low oxidation number /charge density ↓
Smaller splitting - ↓∆ E - Diff colour
Fe(H2O)62+
- Higher energy absorbed
- Blue wavelength absorb to excite electron
Fe(H2O)63+
V(H2O)65+ +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)65+
Electromagnetic Spectrum
Electromagnetic spectrum ranges from Radiowaves to Gamma waves. - Form of energy - Shorter wavelength -> Higher frequency -> Higher energy - Longer wavelength -> Lower frequency -> Lower energy
Electromagnetic radiation • Travel at speed of light, c = fλ -> 3.0 x 108 m/s • Light Particle – photon have energy given by -> E = hf • Energy photon - proportional to 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.
Click here to view video
Electromagnetic Wave propagation.
Wave
Electromagnetic radiation
Electromagnetic radiation • Moving charges/particles through space • Oscillating wave like property of electric and magnetic field • Electric and magnetic field oscillate perpendicular to each other and perpendicular to direction of wave propagation.
Electromagnetic wave 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
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
Continuous Spectrum Vs Line Spectrum
Light/photon ABSORB by electron
Range Light/photon ABSORB by electron
Light/photon ABSORB by electron
Absorption spectrum is broad/continuous Ions in solution (Sovent)
2
∞ Absorption spectrum for ions in solution ↓
Surrounded by ligand and solvent ↓
Have electronic excitation transition state + vibrational/rotational energy level
↓ Continuous broad spectrum
Gaseous state – only gaseous ion present ↓
Complete vacuum ↓
Well defined spectral line 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/broad spectrum can be absorbed to excite electron to electronic/vibrational/ rotational level
Absorption spectrum 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/broad spectrum can be absorbed to excite electron to electronic/vibrational/ rotational level
Absorption spectrum for ions in solution ↓
Surrounded by ligand and solvent ↓
Have electronic excitation transition state + vibrational/rotational energy level
↓ Continuous broad spectrum
Absorption spectrum is broad/continuous Ions in solution (Solvent)
Whole range of wavelength/broad spectrum can be absorbed to excite electron to
electronic/vibrational/ rotational level
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
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