Chemical Ideas 6.1 Light and the electron.
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Transcript of Chemical Ideas 6.1 Light and the electron.
Chemical Ideas 6.1
Light and the electron.
Sometimes we use the wave model for light …
• λ (lambda)= wavelength
Wavelength increases, Frequency ?
C
decreases
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 λ:
1. If ν is 3.00 m
2. If ν is 30.0 cm
3. If ν is 3.00 mm
Work out λ:
4. If ν
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
5. If the frequency is 1.089 x 106 Hz, what is the energy of each photon?
6. If E = 3.65 x 10-20 J per photon, what is the frequency (ν) of the radiation?
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.
3 2 4 2
?
5
7 etc
1
2
34
6
Why no
• 7 2
• 8 2
• 9 2?
visible ultra violet
E increases
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Balmer 2
E increasing
Lyman ?
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1
Absorption Spectrum of hydrogen.
• Continuous spectrum
• Black lines.
How do the 2 compare?
What happens to electrons?
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• Electrons absorb energy
• Electrons are excited
• Electrons move to higher energy level
• E = h v
Back to the Storyline….
• Photosphere of hot stars emit visible or UV light
• Particles in the chromosphere absorb some of the light
• Every element has a different absorption spectrum
• Have a look at assignment 5
H
He
Fe
X (g) X+(g) + e-Ionisation
energy
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Energy needed to
remove one e- from 1 mole
of atoms of a gaseous element
Ground state electron?
7. Use ΔE = hν to calculate the energy per photon corresponding to this frequency (in J).
h = 6.63 x 10-34 J Hz -1.8. Ionisation energy has units of kJ mol-1. You
have calculated the energy required to ionise a single atom. Work out the ionisation energy for hydrogen. L = 6.02 x 1023 mol-1.
Convergence limit = 3.27 x 1015 Hz