 Chemical Ideas 6.1 Light and the electron.. Sometimes we use the wave model for light … λ (lambda)= wavelength.

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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 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

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

Sometimes we use the particle model … Packages of energy are called photons Light is a stream of photons E = 6.63 x10 -34 x 4.5 x 10 14 = 3.0 x 10 -19 J Hz h = 6.63 x 10 -34 J Hz -1 Planck constant

Rearranging again…. E h

E = hν problems … h = 6.63 x 10-34 J Hz -1 Planck constant 5. If the frequency is 1.089 x 10 6 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. 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.

3  2 4  2 ?

5 7 etc 1 2 3 4 6 Why no 7  2 8  2 9  2?

visibleultra violet E increases

6 1 2 3 4 Balmer  2 E increasing Lyman  ? 1 2 3 4 1

Absorption Spectrum of hydrogen. Continuous spectrum Black lines.

How do the 2 compare?

What happens to electrons? 1 2 3 4 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 1 2 3 4 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 10 23 mol -1. Convergence limit = 3.27 x 10 15 Hz

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