Why are molecules coloured?

Generally, molecules are coloured as they absorb visible frequencies of light, to promote an electron to a higher energy level, so the other (complementary) frequencies of light pass through the sample and are seen. However normally these energy levels are too far apart to correspond to frequencies of visible light.(change in E = hv) In organic molecules, a system of alternating single and double bonds (called a conjugate system or chromophore) usually made of benzene rings or c=c bonds, causes electron energy levels to get smaller and closer together. In transition metals, the metal centres are surrounded by ligands, which causes the normally equal in energy d orbitals to split into two sets of orbitals with different energy levels, which are close enough together in energy that electrons will absorb visible light photons to be promoted from the lower energy d orbitals to the higher energy d orbitals.

Answered by Callum B. Chemistry tutor

3489 Views

See similar Chemistry A Level tutors

Related Chemistry A Level answers

All answers ▸

The pH of pure water can vary depending on the temperature it is held at. Does that mean pure water can be acidic or alkaline?


In terms of structure and bonding explain why the boiling point of bromine is different from that of magnesium


State and explain the general trend in the first ionisation energy across a period.


How would you find out whether a reaction is feasible?


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences