Chemical Ideas 6.7

Where does colour come from?

25 questions to see what you’ve

remembered.

More about the colour we see .. Key stage 3 stuff.

1. What colour is the light reaching my eye? Explain.

Red filter

transmit absorb reflect

2. What colour is the light reaching my eye? Explain.

Blue filter

transmit absorb reflect

3. What colour is the light reaching my eye? Explain.

Colourless glass

transmit absorb reflect

4. What colour does the ball

look? Explain.

transmit absorb reflect

5. What colour does the ball

look? Explain.

transmit absorb reflect

6. What colour does the ball

look? Explain.

transmit absorb reflect

7. What colour does the ball look? Explain

transmit absorb reflect

8. What colour does the ball

look? Explain.

transmit absorb reflect

9. The rays are …

•A. Refracted

•B. Reflected

•C. Dispersed

•D. Converged

10. Name the 3 primary colours of light …

Chemical Ideas 6.1

Light and the electron.

Sometimes we use the wave model for light …

• λ (lambda)= wavelength

11. Wavelength increases, Frequency ?

C

•12. Sketch the e.m.s. and use arrows to

mark:

•Increasing energy•Increasing wavelength•Increasing frequency

C = λν problems….

Work out v:

13. If λ is 3.00 m

14 If λ is 30.0 cm

15. If λ is 3.00 mm

Work out λ:

16. If ν is 3.00 x 1010 Hz

c = 3.00x108 m s-1

Sometimes we use the particle model …hE

• Packages of energy are called photons

• Light is a stream of photons

• E = 6.63 x10-34 x 4.5 x 1014 = 3.0 x 10-19 J

14105.4 x Hz

h = 6.63 x 10-34 J Hz -1

Planck constant

E = hν problems …

• h = 6.63 x 10-34 J Hz -1

• Planck constant

17. If the frequency is 1.089 x 106 Hz, what is the energy of each photon?

18. If E = 3.65 x 10-20 J per photon, what is the frequency (ν) of the radiation?

19. Absorption or emission Spectrum of hydrogen?

• Black background

• Coloured lines.

Spectroscopy• Sample of

hydrogen

• High voltage

• Prism

• Electrons can only exist in fixed energy levels.

ΔE

h

E

• Electrons absorb energy and move to a higher energy level.

• The electrons drop back to a lower energy level and emit energy.

• The frequency of the radiation emitted depends on ΔE.

20. Red? 21. Blue/green?

?

5

7 etc

1

2

34

6

22. Why no

• 7 2

• 8 2

• 9 2?

23. What happens to electrons?

1

234

Chemical Ideas 6.2What happens when

radiation interacts with matter?

Molecules are made of more than one atom but they still have

electrons.• Electronic

transitions

Vis + UV

24. Molecules move ! How?

25.There are vibrational energy levels as well as electronic energy level . ΔE in which

region?

The answers …

1. What colour is the light reaching my eye? Explain.

Red filter

Red

2. What colour is the light reaching my eye? Explain.

Blue filter

Blue

3. What colour is the light reaching my eye? Explain.

Colourless glass White

4. What colour does the ball

look? Explain.

Red

5. What colour does the ball

look? Explain.

Black

6. What colour does the ball

look? Explain.

White

7.What colour does the ball

look? Explain.Red

8. What colour does the ball

look? Explain.Black

9. The rays are …

•A. Refracted

•B. Reflected

•C. Dispersed

•D. Converged

10. Name the 3 primary colours of light …

Sometimes we use the wave model for light …

• λ (lambda)= wavelength

11. Wavelength increases, Frequency ?

C

decreases

energy

wavelength

frequency

12.

c = λ ν

υcλ

c

c

νλ

c = speed of light = 3.00 x 108 m s-1

λ = wavelength m lambda

ν = frequency Hz ( or s-1 ) nu

c

Use m

for λ

C = λν problems….

Work out v:

13. If λ is 3.00 m

14. If λ is 30.0 cm

15. If λ is 3.00 mm

Work out λ:

16. If ν is 3.00 x 1010 Hz

c = 3.00x108 m s-1

Sometimes we use the particle model …hE

• Packages of energy are called photons

• Light is a stream of photons

• E = 6.63 x10-34 x 4.5 x 1014 = 3.0 x 10-19 J

14105.4 x Hz

h = 6.63 x 10-34 J Hz -1

Planck constant

Rearranging again….

hE

h

E

E

h

E = hν problems …

• h = 6.63 x 10-34 J Hz -1

• Planck constant

17. If the frequency is 1.089 x 106 Hz, what is the energy of each photon?

18. If E = 3.65 x 10-20 J per photon, what is the frequency (ν) of the radiation?

19.

• Black background

• Coloured lines.

emission

Spectroscopy• Sample of

hydrogen

• High voltage

• Prism

• Electrons can only exist in fixed energy levels.

ΔE

h

E

• Electrons absorb energy and move to a higher energy level.

• The electrons drop back to a lower energy level and emit energy.

• The frequency of the radiation emitted depends on ΔE.

20. 3 2 21. 4 2

?

5

7 etc

1

2

34

6

22. Why no

• 7 2

• 8 2

• 9 2?

visible ultra violet

E increases

6

1

234

Balmer 2

E increasing

Lyman ?

1

234

1

Absorption Spectrum of hydrogen.

• Continuous spectrum

• Black lines.

How do the 2 compare?

23.What happens to electrons?

1

234

• Electrons absorb energy

• Electrons are excited

• Electrons move to higher energy level

• E = h v

Molecules are made of more than one atom but they still have

electrons.• Electronic

transitions

Vis + UV

24. Molecules move ! How?

25. There are vibrational energy levels as well as electronic

energy level ..

I.R.

• Electronic transitions

Vis + UV

• Rotational transitions

• Vibrational transitions

Microwave

I.R.

Chemical Ideas 6.7

Where does colour come from?

•Absorb

•Transmits

•Complementary

•Absorb

•Transmits

•Complementary

•Absorb

•Transmits

•Complementary

X2

X2*

e-

e-

filter

meter

photocell

cuvette

concentration

absorbance Absorbance α concentration