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Radiation and Matter
Electromagnetic radiation can interact with matter, transferring energy to the
chemicals involved.

The chemicals absorb energy and this can make changes happen in the chemicals.

What changes occur depend on:

The chemical involved
The amount of energy involved

Molecules are doing energetic things all the time ­…

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Electrons can occupy definite energy levels.

The electronic energy of an atom or molecule changes when an electron moves from
one level to another.

We say that electronic energy is quantised, with fixed levels.

All these other types of energy (translational, rotational and vibrational) are quantised too.

For example:

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Different Energy Changes for Different Parts
of the Spectrum
The spacing between different vibrational energy levels corresponds to the infrared part of
the spectrum.

We sense infrared radiation as heat. You can sense infrared radiation when you feel the
warmth radiated by a fire.

The radiation makes bonds in the…

Page 4

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Electronic Changes and Ultraviolet Radiation
Electrons occupy definite energy levels in atoms.

The gaps between these electronic energy levels correspond to the energy of visible and
ultraviolet light. So electrons jump to higher energy levels when an atom absorbs photons of
visible or ultraviolet radiation.

The same kind of thing…


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