Why do transition metals form coloured solutions?

White light is a mixture of different colours of light (e.g red, green and blue) and each colour has a different wavelength. For something to have colour, it needs to absorb certain wavelengths (or colours) of light. What's left over is what we see. So how do transition metals do that?

When they dissolve in solution, they don't exist as isolated ions but are surrounded by ligands (in aqueous solutions they're water molecules). These ligands donate a pair of electrons to the positive metal ion in a dative covalent bond. For example, iron forms [Fe(H2O)6]2+ which is pale green. These ions are called complex ions.

All transition metals have electrons in their d orbitals, which are electrostastically repelled by those donated by the ligands. Since d orbitals have different shapes and orientations, they're not all repelled to the same extent: for an octahedral complex ion, the ligands are placed at the 6 corners of the octadedron. The dzand dx2-y2 are pointing to those corners and so are repelled a lot. The other three d orbitals don't point directly towards the ligands and so are repelled less. Therefore, the dzand dx2-yorbitals are at a higher energy than the other three, and so an energy gap is created, called d orbital splitting.

When light shines on the solution, wavelengths of light that have an energy equal to the energy gap between the two sets d orbitals take electrons in the lower energy orbital to one at the higher energy level. The wavelengths left behind are what we see!

Yusuf B. A Level Chemistry tutor, GCSE Chemistry tutor, GCSE Physics ...

1 year ago

Answered by Yusuf, an A Level Chemistry tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


£24 /hr

Nketia O.

Degree: Pharmacy (Masters) - Durham University

Subjects offered:Chemistry, Physics+ 1 more


“Hello! My name’s Nketia. I got an A* in A-Level Biology and an A in A-Level Chemistry. I’m a second-year Pharmacy student who is ready to teach others.”

£24 /hr

Julia M.

Degree: Sustainable Agriculture and Food Security (Masters) - Edinburgh University

Subjects offered:Chemistry, Maths+ 1 more


“Enthusiastic friendly tutor looking for curious and ambitious students for fun and relaxed lessons”

£24 /hr

Pooja D.

Degree: Medicine (Bachelors) - Birmingham University

Subjects offered:Chemistry, Science+ 6 more

-Personal Statements-
-Medical School Preparation-

“I have tutored for the past 4 years and have gathered many ways of teaching concepts to students in a way that is easily-digestible and understandable. ”

About the author

Yusuf B.

Currently unavailable: for new students

Degree: Chemistry (Bachelors) - Durham University

Subjects offered:Chemistry, Physics


“Who are you?I'm a chemistry student at Durham University who has a (slightly nerdy) passion for not just chemistry but all things science. During my A-levels I really got gripped by how interesting studying the natural world is, and ...”

You may also like...

Other A Level Chemistry questions

What is optical isomerism and how can you distinguish between optical isomers?

How do mass spectrometers work?

What is the definition of "Enthalpy Change of Formation"

What is Gibbs Free Energy?

View A Level Chemistry tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss