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Published byBerenice Sibson Modified about 1 year ago

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Chemical Ideas 6.1 Light and the electron.

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Sometimes we use the wave model for light … λ (lambda)= wavelength

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Wavelength increases, Frequency ? C decreases

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c = λ ν c νλ c = speed of light = 3.00 x 10 8 m s -1 λ = wavelength m lambda ν = frequency Hz ( or s -1 ) nu Use m for λ

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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 = 3.00x10 8 m s -1

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Sometimes we use the particle model … Packages of energy are called photons Light is a stream of photons E = 6.63 x x 4.5 x = 3.0 x J Hz h = 6.63 x J Hz -1 Planck constant

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Rearranging again…. E h

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E = hν problems … h = 6.63 x J Hz -1 Planck constant 5. If the frequency is x 10 6 Hz, what is the energy of each photon? 6. If E = 3.65 x J per photon, what is the frequency (ν) of the radiation?

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Emission Spectrum of hydrogen. Black background Coloured lines.

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Spectroscopy Sample of hydrogen High voltage Prism

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Electrons can only exist in fixed energy levels. ΔEΔE 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.

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3 2 4 2 ?

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5 7 etc Why no 7 2 8 2 9 2?

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visibleultra violet E increases

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Balmer 2 E increasing Lyman ?

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Absorption Spectrum of hydrogen. Continuous spectrum Black lines.

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How do the 2 compare?

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What happens to electrons? Electrons absorb energy Electrons are excited Electrons move to higher energy level E = h v

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Back to the Storyline…. Photosphere of hot stars emit visible or UV light Particles in the chromosphere absorb some of the light

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Every element has a different absorption spectrum Have a look at assignment 5 H He Fe

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X (g) X + (g) + e - Ionisation energy Energy needed to remove one e - from 1 mole of atoms of a gaseous element Ground state electron?

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7. Use ΔE = hν to calculate the energy per photon corresponding to this frequency (in J). h = 6.63 x J Hz 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 mol -1. Convergence limit = 3.27 x Hz

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