Only the ions that have electrons in d-orbital will be coloured. The ions in which d-orbital is empty will be colourless.
Element |
Atomic
Number |
Ionic
State |
Electronic configuration in ionic
state |
Ti |
22 |
T13+ |
[Ar] 3d1 |
v |
23 |
V3+ |
[Ar] 3d2 |
Cu |
29 |
Cu+ |
[Ar] 3d10 |
Sc |
21 |
Sc3+ |
[Ar] |
Mn |
25 |
Mn2+ |
[Ar] 3d5 |
Fe |
26 |
Fe3+ |
[Ar] 3d5 |
Co |
27 |
Co2+ |
[Ar] 3d7 |
From the above table, it can be easily observed that only Sc3+ has an empty d-orbital. All
other ions, except Sc3+, will be coloured in aqueous solution because of d−d transitions.