IB Chemistry on Absorption Spectrum and Line Emission/Absorption Spectrum

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

https://www.wou.edu/las/physci/ch462/tmcolors.htm

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


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

http://www.youtube.com/watch?feature=player_embedded&v=sFAGQLokym4

http://www.youtube.com/watch?feature=player_embedded&v=sFAGQLokym4

http://www.youtube.com/watch?v=hDt2OUnOcug&feature=related

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)


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



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



Ti3+ [Ar] 3d1

3d yz 3d xy 3d xz 3d Z2 3d x

2 - y2

Ti3+ [Ar] 3d1 ∆E




V3+ [Ar] 3d2 Green


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





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



Cu2+ [Ar] 3d9


2 - y2

Cu2+ [Ar] 3d9 ∆E




V3+ [Ar] 3d2 Green


Mn2+ [Ar] 3d5 Pink

Fe2+ [Ar] 3d6 Green

Co2+ [Ar] 3d7 Pink

Ni2+ [Ar] 3d8 Green

Cu2+ [Ar] 3d9 Blue


Red / orange wavelength

- Abosrb to excite electron

О

Cu2+





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



Sc3+ [Ar] 3d0


2 - y2

Sc3+ [Ar] 3d0 ∆E




V3+ [Ar] 3d2 Green


Mn2+ [Ar] 3d5 Pink

Fe2+ [Ar] 3d6 Green

Co2+ [Ar] 3d7 Pink

Ni2+ [Ar] 3d8 Green

Cu2+ [Ar] 3d9 Blue


All wavelength transmitted

Sc3+

NO absorption

white





Why Zn 3+ ion solution is colourless ?

Colourless



Zn2+ [Ar] 3d10


2 - y2

Zn2+ [Ar] 3d10 ∆E




V3+ [Ar] 3d2 Green


Mn2+ [Ar] 3d5 Pink

Fe2+ [Ar] 3d6 Green

Co2+ [Ar] 3d7 Pink

Ni2+ [Ar] 3d8 Green

Cu2+ [Ar] 3d9 Blue


Zn2+

All wavelength transmitted Splitting 3d orbital

FULLY FILLED

NO absorption light


NO absorption

white





Why Cu+ ion solution is colourless ?

Colourless



Cu+ [Ar] 3d10


2 - y2

Cu+ [Ar] 3d10 ∆E

Cu+

All wavelength transmitted Splitting 3d orbital

FULLY FILLED

NO absorption light





V3+ [Ar] 3d2 Green


Mn2+ [Ar] 3d5 Pink

Cu+ [Ar] 3d10 Colourless

Cu2+ [Ar] 3d9 Blue

white

NO absorption




No ligand/Water • NO Splitting 3d orbital • 3d orbital equal energy

Why Cu3+ ion anhydrous is colourless ?


NO ligand • 3d orbital split • five 3d orbital equal in energy

Cu2+ [Ar] 3d9


2 - y2

Cu2+ [Ar] 3d9




V3+ [Ar] 3d2 Green


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


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



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


I- < Br- < CI- < F- < OH- < C2O42- < H2O < SCN- < NH3 < en < Co/CN

Transition Metal – Colour Complexes Colour- Splitting 3d orbital by ligand


Greater splitting - ↑∆E Diff colour


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


∆E ∆E



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



Greater splitting - ↑∆E - Diff colour


Smaller splitting - ↓∆ E - Diff colour

Spectrochemical series – Weak ligand → Strong Ligand

WEAK ligand – small splitting


∆E ∆E



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

↓


↓

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


- Blue wavelength absorb to excite electron


- Violet wavelength absorb to excite electron


High nuclear charge / charge density ↓


Low nuclear charge /charge density ↓


Nuclear charge on metal ion

Low nuclear charge – small splitting


∆E ∆E

High nuclear charge – greater splitting


Highest nuclear charge/charge density ↓

Greatest splitting - ↑∆E- Diff colour

∆E

Fe(H2O)63+ +3 YELLOW

HIGHEST nuclear charge – greatest splitting

Fe(H2O)63+


- Green wavelength absorb to excite electron

V(H2O)65+ +5 YELLOW/GREEN

Mn(H2O)62+ V(H2O)6

5+

Oxidation number - +3

↓


↓

Greater splitting ∆E

↓

Higher energy wavelength absorb

Oxidation number - +2

↓

Weak ESF atrraction bet –ve ligand

↓

Smaller splitting ∆E

↓

Low energy wavelength absorb


Higher oxidation number/charge density ↓


Lower ESF attraction – small splitting


∆E ∆E



∆E

Fe(H2O)63+ +3 Yellow


- Red wavelength absorb to excite electron

Fe(H2O)62+ +2 Green

Oxidation number on metal ion

Low oxidation number /charge density ↓


Fe(H2O)62+


- 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


- 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.

https://www.youtube.com/watch?v=NQxaWBGK4Oc

https://www.youtube.com/watch?v=NQxaWBGK4Oc

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

https://www.youtube.com/watch?v=lwfJPc-rSXw

http://micro.magnet.fsu.edu/primer/java/polarizedlight/emwave/

https://www.youtube.com/watch?v=lwfJPc-rSXw

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


1


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


1


3



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


1

2

3

Range Light/photon ABSORB by electron




Energy lost in small steps

Absorbed by solvent

Lost to environment

Education

IB Chemistry on Absorption Spectrum and Line Emission/Absorption Spectrum