Transition metal

In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings:

Colored compounds

We observe color as varying frequencies of electromagnetic radiation in the visible region of the electromagnetic spectrum. Different colors result from the changed composition of light after it has been reflected, transmitted or absorbed after hitting a substance.

Related Topics:
Light - Reflected - Absorbed

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Because of their structure, transition metals form many different colored ions and complexes.

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Color even varies between the different ions of a single element - MnO4? (Mn in oxidation state 7+) is a purple compound, whereas Mn2+ is pale-pink.

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Complex formation can play a part in determining color in a transition compound.

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This is because of the effect that ligands have on the 3d orbital. Ligands pull on some of the 3d electrons and split them in to higher and lower (in terms of energy) groups.

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Electromagnetic radiation is only absorbed if its frequency is proportional to the difference in energies between two energy states present in an atom (through the formula e=hf.)

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When light hits an atom which has had its 3d orbitals split, some of the electrons become promoted to the higher group. Compared to an un-complexed ion, different frequencies can be absorbed, hence different colors are observed.

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The color of a complex depends on:

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• the nature of the metal ion, specifically the number of electrons in the d orbitals
• the arrangement of the ligands around the metal ion (for example geometric isomers can display different colors)
• the nature of the ligands surrounding the metal ion. The stronger the ligands then the greater the energy difference between the split high and low 3d groups.

The complex formed by the d block element zinc (though not strictly a transition element) is colorless, because the 3d orbitals are full - no electrons are able to move up to the higher group.

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