IB Chemistry on Line Emission Spectrum, Bohr Model and Electromagnetic Spectrum

1. Tutorial on Electromagnetic
Radiation, Emission Line spectrum and
Bohr Model.
Prepared by
Lawrence Kok
http://lawrencekok.blogspot.com

2. 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

3. 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
Wavelength, λ - long 
Frequency, f
- low 
Wavelength, λ - short 
Inverse relationship between- λ and f
Frequency, f
- high 

4. 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
Wavelength, λ - long 
Frequency, f
- low 
Wavelength, λ - short 
Inverse relationship between- λ and f
Frequency, f
- high 
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
Plank constant
• proportionality constant bet energy and freq
Excellent video wave propagation
Click here to view.

5. Electromagnetic Wave propagation.
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 radiation
Electromagnetic wave propagation
Click here to view video

6. Electromagnetic Wave propagation.
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 radiation
Electromagnetic wave propagation
Click here to view video
Wave
Wave – wavelength and frequency
- travel at speed of light

7. Electromagnetic Wave propagation.
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 radiation
Electromagnetic wave propagation
Click here to view video
Violet
λ = 410nm
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
Wave
Wave – wavelength and frequency
- travel at speed of light
Red
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

8. Electromagnetic Wave propagation.
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 radiation
Is it a particle or Wave?
Click to view video -Wave-particle duality
Wave
Wave – wavelength and frequency
- travel at speed of light

9. Electromagnetic Wave propagation.
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 radiation
Is it a particle or Wave?
Click to view video -Wave-particle duality
Wave
Wave – wavelength and frequency
- travel at speed of light
Simulation on Electromagnetic Propagation
Click here to view simulation
Click here to view simulation
Click here to view simulation

10. Electromagnetic Wave
Violet
Red
λ = 410nm
λ = 700nm
f = c/λ
= 3 x 108/410 x 10-9
= 7.31 x 1014 Hz
f = c/λ
= 3 x 108/700 x 10-9
= 4.28 x 1014 Hz
Wavelength – Distance bet two point with same phase, bet crest/troughs – unit nm
Frequency – Number of cycle/repeat per unit time (cycles in 1 second) – unit Hz

11. Electromagnetic Wave
Violet
Red
λ = 410nm
λ = 700nm
f = c/λ
= 3 x 108/410 x 10-9
= 7.31 x 1014 Hz
f = c/λ
= 3 x 108/700 x 10-9
= 4.28 x 1014 Hz
Wavelength – Distance bet two point with same phase, bet crest/troughs – unit nm
Frequency – Number of cycle/repeat per unit time (cycles in 1 second) – unit Hz
Which wave have higher frequency, if both have same speed reaching Y same time?
Violet
X
Y
Red

12. Electromagnetic Wave
Violet
Red
λ = 410nm
λ = 700nm
f = c/λ
= 3 x 108/410 x 10-9
= 7.31 x 1014 Hz
f = c/λ
= 3 x 108/700 x 10-9
= 4.28 x 1014 Hz
Wavelength – Distance bet two point with same phase, bet crest/troughs – unit nm
Frequency – Number of cycle/repeat per unit time (cycles in 1 second) – unit Hz
Which wave have higher frequency, if both have same speed reaching Y same time?
Violet
X
Click here on excellent video red /violet wave
Click here to view video energy photon
Y
Light travel same speed
Red flippers – long λ - less frequent
Violet shoes – short λ - more frequent
Red

13. Continuous Spectrum Vs Line Spectrum
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

14. Continuous Spectrum Vs Line Spectrum
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
Electrons from excited state
Excited state
Emit radiation
when drop to ground state
Radiation emitted
Emission Spectrum
Ground state
http://www.astrophys-assist.com/educate/orion/orion02.htm

15. Continuous Spectrum Vs Line Spectrum
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
Electrons from excited state
Excited state
Electrons in excited state
Emit radiation
when drop to ground state
Radiation absorbed
Radiation emitted
Absorb radiation
to excited state
Emission Spectrum
Ground state
http://www.astrophys-assist.com/educate/orion/orion02.htm
Electrons from ground state

16. Line Emission Spectroscopy
Line Emission Spectra for Hydrogen
Energy supplied to atoms
• Electrons excited - ground to excited states
• Electrons exist fixed energy level (quantum)
• Electrons transition from higher to lower,
emit energy of particular wavelength/frequency - photon
• Higher the energy level, smaller the difference in energy
bet successive energy level.
• Spectrum converge (get closer) with increase freq.
• Lines spectrum converge- energy levels also converge
• Ionisation energy determined (Limit of convergence)
UV region
Lyman Series
n=∞ → n= 1
Visible region
Balmer Series
n=∞ → n= 2
IR region
Paschen Series
n=∞ → n= 3

17. Line Emission Spectroscopy
Line Emission Spectra for Hydrogen
Energy supplied to atoms
• Electrons excited - ground to excited states
• Electrons exist fixed energy level (quantum)
• Electrons transition from higher to lower,
emit energy of particular wavelength/frequency - photon
• Higher the energy level, smaller the difference in energy
bet successive energy level.
• Spectrum converge (get closer) with increase freq.
• Lines spectrum converge- energy levels also converge
• Ionisation energy determined (Limit of convergence)
UV region
Lyman Series
n=∞ → n= 1
Visible region
Balmer Series
n=∞ → n= 2
IR region
Paschen Series
n=∞ → n= 3
Line Emission Spectra
• Energy supplied
• Electrons surround nucleus in allowed energy states (quantum)
• Excited electron return to lower energy level, photon with
discrete energy/wavelength (colour) given out.
• Light pass through spectroscope (prism/diffraction grating) to separate
out diff colours
N= 6-2
410nm
N= 5-2
434nm
N= 4-2
486nm
N = 3-2,
656nm
Visible region- Balmer Series

18. Line Emission Spectroscopy
Line Emission Spectra for Hydrogen
Energy supplied to atoms
• Electrons excited - ground to excited states
• Electrons exist fixed energy level (quantum)
• Electrons transition from higher to lower,
emit energy of particular wavelength/frequency - photon
• Higher the energy level, smaller the difference in energy
bet successive energy level.
• Spectrum converge (get closer) with increase freq.
• Lines spectrum converge- energy levels also converge
• Ionisation energy determined (Limit of convergence)
UV region
Lyman Series
n=∞ → n= 1
Visible region
Balmer Series
n=∞ → n= 2
IR region
Paschen Series
n=∞ → n= 3
Line Emission Spectra
• Energy supplied
• Electrons surround nucleus in allowed energy states (quantum)
• Excited electron return to lower energy level, photon with
discrete energy/wavelength (colour) given out.
• Light pass through spectroscope (prism/diffraction grating) to separate
out diff colours
Videos on line emission
N= 6-2
410nm
Click here to view video
Click here to view video
N= 5-2
434nm
N= 4-2
486nm
N = 3-2,
656nm
Visible region- Balmer Series

19. Hydrogen Emission Spectroscopy – Visible region (Balmer Series)
Line Emission Spectra for Hydrogen
Excited state
5
4
3
2
Visible region
Balmer Series
n=∞ → n= 2
Ground state
Click here for detail notes
1
Click here video line emission spectrum

20. Hydrogen Emission Spectroscopy – Visible region (Balmer Series)
Line Emission Spectra for Hydrogen
Hydrogen discharge tube
Excited state
5
4
3
2
Visible region
Balmer Series
n=∞ → n= 2
Ground state
Click here for detail notes
1
Click here video line emission spectrum
Hydrogen Emission Spectroscopy

21. Hydrogen Emission Spectroscopy – Visible region (Balmer Series)
Line Emission Spectra for Hydrogen
Hydrogen discharge tube
Excited state
Hydrogen Emission Spectroscopy
5
4
3
n= 5-2
n = 3-2
n= 4-2
2
λ = 434nm
Visible region
Balmer Series
n=∞ → n= 2
Ground state
1
f = c/λ
= 3 x 108/434 x 10-9
= 6.90 x 1014 Hz
λ = 486nm
λ = 656nm
f = c/λ
= 3 x 108/656 x 10-9
= 4.57 x 1014 Hz
E = hf
= 6.62 x 10-34 x 6.90 x 1014
= 4.56 x 10-19 J
More energetic violet line
Click here for detail notes
Click here video line emission spectrum
E = hf
= 6.62 x 10-34 x 4.57 x 1014
= 3.03 x 10-19 J
Less energetic red line

22. Bohr Model for Hydrogen Atom – Ionization Energy
Bohr Model
Energy level
Electronic Transition bet levels
Niels Bohr Model (1913)
•
•
•
Electrons orbit nucleus.
Orbits with discrete energy levels – Quantized.
Transition electron bet diff levels by absorb/emit radiation
with frequency, f determined by energy diff bet levels -ΔE = hf
• Energy light emit/absorb equal to diff bet energy levels

23. Bohr Model for Hydrogen Atom – Ionization Energy
Bohr Model
Energy level
Electronic Transition bet levels
Niels Bohr Model (1913)
•
•
•
Electrons orbit nucleus.
Orbits with discrete energy levels – Quantized.
Transition electron bet diff levels by absorb/emit radiation
with frequency, f determined by energy diff bet levels -ΔE = hf
• Energy light emit/absorb equal to diff bet energy levels
Light emitted equal to difference
bet energy levels, -ΔE = hf
Ionization energy
Transition electron from 1 ->∞
∞
Plank equation
Higher energy level n, smaller the difference
in energy bet successive energy level.
5
4
3
ΔE = hf
Light given off
2
Light energy - ΔE = hf
Frequency = ΔE/h
1

24. Bohr Model for Hydrogen Atom – Ionization Energy
Energy level
Bohr Model
Electronic Transition bet levels
Niels Bohr Model (1913)
•
•
•
Electrons orbit nucleus.
Orbits with discrete energy levels – Quantized.
Transition electron bet diff levels by absorb/emit radiation
with frequency, f determined by energy diff bet levels -ΔE = hf
• Energy light emit/absorb equal to diff bet energy levels
Light emitted equal to difference
bet energy levels, -ΔE = hf
Ionization energy
Transition electron from 1 ->∞
∞
Plank equation
Higher energy level n, smaller the difference
in energy bet successive energy level.
5
4
3
ΔE = hf
2
Light given off
Light energy - ΔE = hf
Frequency = ΔE/h
1
line converge
UV region
Lyman Series
n=∞ → n= 1
Increase freq 
Line spectrum converge (get closer) with increase freq
Ionisation energy determined (Limit of convergence)
line converge
Visible region
Balmer Series
n=∞ → n= 2
Increase freq 
Line spectrum converge (get closer) with increase freq
Lines in spectrum converge- energy levels also converge

25. Energy Level/Ionization Energy Calculation
∞
Formula - energy level, n (eV)
n = energy level
5
5
4
4
3
3
1
2
2
Energy level, n= 3
= -13.6/n2
= -13.6/32
= -1.51 eV
3
Energy level, n= 2
= -13.6/n2
= -13.6/22
= -3.4 eV
4
Energy level, n= 1
= -13.6/n2
= -13.6/1
= -13.6 eV
2
constant
10-19 J
1eV – 1.6 x
h = 6.626 x 10-34 Js
1
1

26. Energy Level/Ionization Energy Calculation
∞
Formula - energy level, n (eV)
n = energy level
5
5
4
4
3
3
1
2
2
Energy level, n= 3
= -13.6/n2
= -13.6/32
= -1.51 eV
3
Energy level, n= 2
= -13.6/n2
= -13.6/22
= -3.4 eV
4
Energy level, n= 1
= -13.6/n2
= -13.6/1
= -13.6 eV
2
constant
10-19 J
1eV – 1.6 x
h = 6.626 x 10-34 Js
1
1
Higher energy level, n
- more unstable electron
- More + ve ( less negative)
- More energetic
5
6
Ionization energy
Transition electron from 1 ->∞
Lower energy level, n
- more stable electron
- more – ve (-13.6eV)
- Less energetic

27. Energy Level/Ionization Energy Calculation
Energy difference bet level 3 to 2
∞
Formula - energy level, n (eV)
n = energy level
5
1
4
4
3
Energy difference, n= 3-2
= -1.51 – (-3.4) eV
= 1.89 eV
= 1.89 x 1.6 x 10-19 J
= 3.024 x 10-19 J
5
3
1
2
Energy level, n= 3
= -13.6/n2
= -13.6/32
= -1.51 eV
3
Energy level, n= 2
= -13.6/n2
= -13.6/22
= -3.4 eV
4
Energy level, n= 1
= -13.6/n2
= -13.6/1
= -13.6 eV
Light given off
2
Light energy - ΔE = hf
Frequency, f = ΔE/h
2
2
constant
3
10-19 J
Frequency, f = ΔE/h
f = 3.024 x 10-19 /6.626 x 10-34
= 4.56 x 1015 Hz
4
λ = c/f
= 3 x 108/4.56 x 1015
= 657 x 10-9
= 657nm
1eV – 1.6 x
h = 6.626 x 10-34 Js
1
1
Higher energy level, n
- more unstable electron
- More + ve ( less negative)
- More energetic
5
Light given off
6
Ionization energy
Transition electron from 1 ->∞
Lower energy level, n
- more stable electron
- more – ve (-13.6eV)
- Less energetic

28. Ionization Energy for Hydrogen Atom
∞
1
n = energy level
5
∞
5
4
4
3
Ionization energy
Min energy to remove 1 mole electron from
1 mole of element in gaseous state
M(g)  M+ (g) + e
3
2
Ionization energy
Transition electron from 1 ->∞
Energy Absorb
2
2
3
Energy level, n= ∞
= -13.6/n2
= -13.6/∞
= o eV
4
Energy level, n= 1
= -13.6/n2
= -13.6/1
= -13.6 eV
electron
Light/photon ABSORB by electron
1
1

29. Ionization Energy for Hydrogen Atom
∞
1
n = energy level
5
∞
5
4
4
3
Ionization energy
Min energy to remove 1 mole electron from
1 mole of element in gaseous state
M(g)  M+ (g) + e
3
2
Ionization energy
Transition electron from 1 ->∞
Energy Absorb
2
2
3
Energy level, n= ∞
= -13.6/n2
= -13.6/∞
= o eV
4
Energy level, n= 1
= -13.6/n2
= -13.6/1
= -13.6 eV
electron
Light/photon ABSORB by electron
1
1
5
6
Energy difference, n= 1-> ∞
= 0 – (-13.6) eV
= 13.6 eV
= 13.6 x 1.6 x 10-19 J
= 2.176 x 10-18 J for 1 electron
Energy absorb for 1 MOLE electron
- 2.176 x 10-18 J - 1 electron
- 2.176 x 10-18 x 6.02 x 1023 J - 1 mole
- 1309kJ mol-1

30. Light given off, electronic transition from high -> low level
Light given off
Energy Released
∞
Ionization Energy for Hydrogen Atom
1
n = energy level
5
Energy difference, n= 3-2
= -1.51 – (-3.4) eV
= 1.89 eV
= 1.89 x 1.6 x 10-19 J
= 3.024 x 10-19 J
2
4
4
3
Energy difference bet level 3 to 2
1
∞
5
Ionization energy
Min energy to remove 1 mole electron from
1 mole of element in gaseous state
M(g)  M+ (g) + e
3
2
Ionization energy
Transition electron from 1 ->∞
Light given off
Energy Absorb
2
2
3
3
Frequency, f = ΔE/h
f = 3.024 x 10-19 /6.626 x 10-34
= 4.56 x 1015 Hz
4
Energy level, n= 1
= -13.6/n2
= -13.6/1
= -13.6 eV
Light energy - ΔE = hf
Frequency, f = ΔE/h
4
Energy level, n= ∞
= -13.6/n2
= -13.6/∞
= o eV
electron
Light/photon ABSORB by electron
1
5
1
λ = c/f
= 3 x 108/4.56 x 1015
= 657 x 10-9
= 657nm
Light given off
5
6
Energy difference, n= 1-> ∞
= 0 – (-13.6) eV
= 13.6 eV
= 13.6 x 1.6 x 10-19 J
= 2.176 x 10-18 J for 1 electron
Energy absorb for 1 MOLE electron
- 2.176 x 10-18 J - 1 electron
- 2.176 x 10-18 x 6.02 x 1023 J - 1 mole
- 1309kJ mol-1

31. Energy Level/Ionization Energy Calculation
n = energy level
Energy/Wavelength – Plank/Rydberg Equation
∞
Formula – Plank Equation
5
5
4
4
ΔE = hf
3
3
∞
Rydberg Equation to find wavelength
2
2
R = Rydberg constant
R = 1.097 x 107 m-1
1
1
Nf = final n level
Ni = initial n level

32. Energy photon- high -> low level
1
Electron transition from 3 -> 2
Energy Level/Ionization Energy Calculation
n = energy level
Energy/Wavelength – Plank/Rydberg Equation
Light given off
Formula – Plank Equation
5
Rydberg Eqn find wavelength emit
∞
5
4
4
ΔE = hf
3
3
∞
Rydberg Equation to find wavelength
2
2
2
nf = 2, ni = 3
R = 1.097 x 107
3
R = Rydberg constant
R = 1.097 x 107 m-1
4
5
λ = 657 x 10-9
= 657 nm
f = c/λ
= 3 x 108/657 x 10-9
= 4.57 x 1014 Hz
Light given off
1
1
Nf = final n level
Ni = initial n level

33. Energy photon- high -> low level
1
Electron transition from 3 -> 2
Energy Level/Ionization Energy Calculation
n = energy level
Energy/Wavelength – Plank/Rydberg Equation
Light given off
Formula – Plank Equation
5
Rydberg Eqn find wavelength emit
∞
5
4
4
ΔE = hf
3
3
∞
Rydberg Equation to find wavelength
2
2
2
nf = 2, ni = 3
R = 1.097 x 107
3
R = Rydberg constant
R = 1.097 x 107 m-1
4
5
λ = 657 x 10-9
= 657 nm
f = c/λ
= 3 x 108/657 x 10-9
= 4.57 x 1014 Hz
1
1
Click here on energy calculation
Light given off
Click here to view video
Click here to view video
Nf = final n level
Ni = initial n level

34. Light given off, high -> low level
Energy photon-electronic transition from high -> low level
1
Electron transition from 3 -> 2
∞
n = energy level
5
Light given off
4
4
3
3
2
Rydberg Eqn find wavelength emit
∞
5
2
2
nf = 2, ni = 3
R = 1.097 x 107
3
4
5
λ = 657 x 10-9
= 657 nm
f = c/λ
= 3 x 108/657 x 10-9
= 4.57 x 1014 Hz
Light given off
1
1

35. Light given off, high -> low level
Energy photon-electronic transition from high -> low level
1
Electron transition from 3 -> 2
∞
Ionization Energy for Hydrogen Atom
1
n = energy level
5
Rydberg Eqn find wavelength emit
Light given off
∞
5
4
4
3
Ionization energy
Min energy to remove 1 mole electron from
1 mole of element in gaseous state
M(g)  M+ (g) + e
3
Ionization energy
Transition electron from 1 -> ∞
1
2
Energy Absorb
2
2
nf = 2, ni = 3
R = 1.097 x 107
Rydberg Eqn find ionization energy
3
3
electron
Light/photon ABSORB by electron
4
λ = 657 x 10-9
= 657 nm
1
nf = ∞, ni = 1
R = 1.097 x 107
1
4
5
f = c/λ
= 3 x 108/657 x 10-9
= 4.57 x 1014 Hz
Light given off

36. Light given off, high -> low level
Energy photon-electronic transition from high -> low level
1
Electron transition from 3 -> 2
∞
Ionization Energy for Hydrogen Atom
1
n = energy level
5
Rydberg Eqn find wavelength emit
Light given off
∞
5
4
4
3
Ionization energy
Min energy to remove 1 mole electron from
1 mole of element in gaseous state
M(g)  M+ (g) + e
3
Ionization energy
Transition electron from 1 -> ∞
1
2
Energy Absorb
2
2
nf = 2, ni = 3
R = 1.097 x 107
Rydberg Eqn find ionization energy
3
3
electron
Light/photon ABSORB by electron
4
1
λ = 657 x 10-9
= 657 nm
nf = ∞, ni = 1
R = 1.097 x 107
1
4
5
f = c/λ
= 3 x 108/657 x 10-9
= 4.57 x 1014 Hz
λ = 9.11 x 10-8
7
Light given off
Energy absorb for 1 MOLE electron
- 2.179 x 10-18 J - 1 electron
- 2.179 x 10-18 x 6.02 x 1023 J - 1 mole
- 1312kJ mol-1
6
Energy, E = hf
= 6.626 x 10-34 x 3.29 x 1015
= 2.179 x 10-18 J for 1 electron
5
f = c/λ
= 3 x 108/9.11 x 10-8
= 3.29 x 1015 Hz

37. Continuous Spectrum Vs Line Spectrum
Emission Line Spectrum
• Spectrum with discrete wavelength/ frequency
• Excited electrons drop from higher to lower energy level
Continuous Spectrum
Light spectrum with all wavelength/frequency
Excellent simulation on emission spectrum
Click here to view excellent simulation
Click here to view simulation
Emission line spectrum for different elements
Click here spectrum for diff elements
Click here spectrum for diff element
Click here to view simulation
Video on quantum mechanics
Click here on quantum mechanic, structure of atom

38. Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenses
http://creativecommons.org/licenses/
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorial
http://lawrencekok.blogspot.com