Demonstration that the colour of a transition metal is the result of a partially filled d-orbital

1
Demonstration that the colour of a transition
metal is the result of a partially filled
d-orbital
Copper(I) ion - colourless
Copper(II) ion - blue
Write out the electron configuration of a copper
atom, copper(II) ion and a copper(I) ion. Now
using your ideas about d-orbital splitting
explain the colours of each of the test tubes
above.