[tortoise]

Transition metals show varying degrees of colours in different complexes, why?

[movies]

Well, what type of atomic changes are responsible for colors?

[tortoise]

Absorption of energy from the uv-vis region of the electromagnetic spectrum. This energy causes atomic and molecular electronic transitions. Electrons gain sufficient energy inorder to be promoted from lower energy levels to higher ones.But this only partially explains why transition metals are coloured in complexes. Different ligands and the combination of these explains some but, there is still more. With transition metals there's a little more. Like your question, it's to do with atomic structure and arrangement. But that's for you to find out.

Ok, movies?

[movies]

That's a start.

So you know that it involves electrons.  How much do you know about the electronic structure of transition metal complexes?  Have you taken any inorganic chemistry courses?

[tortoise]

me? sorry... no. I am just a high school student and only study chemistry at school.

I think I don't know much about electronic structure metal complexes. I have not taken any inorganic chemistry courses..

I post this question and answer from a friend. I hope everyone here can help me to check it.

[movies]

Ah, okay.

So when electrons relax from an excited (high energy) state to a lower energy state they release energy by emitting a photon (particle of light).  The amount of energy release determines the energy present in the photon.  If the photon has an energy which we can detect with our eyes then we will see it as light.  The color of the light also depends on the energy.  For example, blue light has more energy than red light.

So, to get a colored emission from a metal complex you have to first excite an electron to a higher energy state and then observe the photon emission.  In metal complexes there are a couple of different transitions that occur in the visible range.  The simplest is just a direct metal based electron excitation.  This would occure in just the same way as a free atom excitation would, although it typically involves a d electron.  Another type of excitation is called "metal to ligand charge transfer."  When this happens, an electron from the metal is transfered to a ligand (one of the molecules or atoms that is "stuck" to the metal).  The opposite of this is "ligand to metal charge transfer."  Either of this can result in an observable photon emission.


I'm no inorganic chemist so if anyone sees an error in my description, please post a corretion.