Question

Account for th fact that compunds conatining Ca2+ and Zn2+ are not coloured, whereas compounds containing Fe2+ are coloured.

Answer 1

This is because Fe2+ is a transition metal. Many compounds of transition metals are coloured, while those of compounds in group 1/2 usually aren't.

In addition, solutions of transition metal salts are often coloured.

Does this answer it or do you want more detail about "why" (hint: it's to do with the increased number of electrons - and how they're differently arranged - on transition metals)?

Answer 2

Zn+2 is a d-block metal but it has a full d shell so it would not be colored (+2 meaning it lost 2 of its s electrons). Fe has a partially full d orbital so it would be colored.

Electrons in the 3d sub shell can move between the orbitals.These energy transitions correspond to the energy of visible light (color).

Titanium is also a transition metal (electron config: [Ar] 4s2 3d2), however it is not colored in the +4 oxidation state (but in the +3 state it's violet). In the +4 oxidation state, titanium loses 2 of its s electrons and 2 of its d electrons. It has no 3d electrons left so Ti+4 isn't colored. In the +3 oxidation state, it still has one 3d electron.

Answer 3

Thanks Guys