Chemical Ideas 6'2 What happens when radiation intracts with matter

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Chemical Ideas 6.2What happens when radiation
intracts with matter?
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c ? ?
? wavelength m lambda
c speed of light 3.00 x 108 m s-1
? frequency Hz ( or s-1 ) nu
Use m for ?
c
?
?
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c ?? problems.
c 3.00x108 m s-1

• 1. Work out ? if v 8.19 x 1013 Hz

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Rearranging again.
E
h
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E h? problems

• h 6.63 x 10-34 J Hz -1
• Planck constant

2. If the frequency is 3.5 x 1013 Hz, what is the
energy of each photon? 3. If E 4.6 x 10-17 J
per photon, what is the frequency (?) of the
radiation?
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visible
ultra violet
E increases
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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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Molecules are made of more than one atom but they
still have electrons.

• Electronic transitions

Vis UV
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Molecules move !
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There are vibrational energy levels as well as
electronic energy level ..
I.R.
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There are rotational energy levels as well as
electronic energy level ..
microwave
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• Electronic transitions

• Rotational transitions

Vis UV
Microwave
I.R.

• Vibrational transitions

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Note the range in Table 1, P130
C-F
C-Cl
C-Br
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What could happen to a Cl2 molecule in the
Atmosphere?
Electronic transitions
Visible
Photodissociation radicals
U.V.

Ionisation
U.V.
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Now

• Read CI 6.2 for yourself
• Complete Notes 3, 4 and 5
• Try Q1, 2 and 4 from CI 6.2. Only do Q4 if you
  are doing AS maths!