The d-And-f-Block Elements

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Actinide cations are coloured? Why?

The cations of actinides are coloured because of the presence of unpaired electrons. The colour observed depends on the number of impaired electrons. The colours of some cations are given below:

Cation of actinide

U3+

Np3+

Pu3+

Am3+

Unpaired electrons

3

4

5

6

Colour observed

Red

Violet

Black violet

Pink

The colour is due to electronic transition within the 5f levels. The electronic transitions of actinides are about ten times more intense than those of lanthanides. The difference is due to difference in 4f and 5f electrons.

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