Draw [Cu(H2O)6]2+ and explain why is it blue in colour.

[Cu(H2O)6]2+ is and octahedral shaped complex which I shall draw on the whiteboard.

It is blue for thw following reasons:

When the water ligands bond to the Cu2+ ion, it causes the d orbitals to split into 2 sets at different energy levels. Electrons in the lower energy d-orbitals absorb red light to promote the electrons to a higher energy d-orbital. This means blue light will be reflected and hence the colour of the complex is blue.