Group 7: Halogens
Read our general notes on Risk Assessment
Could you please tell me why iodine is coloured please? What is it that it makes the chemical coloured?
Your second question is by no means simple. There are fifteen different causes that can give rise to colour in chemicals.
Broadly speaking, at room temperature, chemicals are coloured if they reflect, transmit or emit only part of the full white light spectrum.
Iodine is coloured because energy jumps involving the vibrations of the diatomic molecules correspond to energies of photons of visible light. To be more exact the colour arises from a combination of changes in the energy of the molecule involving vibrational and rotational energy levels.
The iodine spectrum is quite complex and includes absortion in the red, orange, yellow and green parts of the spectrum, The light not abosrbed gives rise to the violet colour we see.
Risk assessment
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updated: 26 February 2006
