Question

As you all know, iodine has a purple color when in the vapor phase and when dissolved in non-coordinating solvents such as carbon tetrachloride. What electronic transition is responsible for this?

Answer 1

The purple color of iodine vapor and dissolved iodine in solvents is due to the absorption of visible light, where iodine molecules transition between energy states and reflect unabsorbed wavelengths.

Step-by-step explanation:

The purple color of iodine vapor and the violet color seen when iodine is dissolved in non-coordinating solvents like carbon tetrachloride is due to an electronic transition known as an absorption of visible light by the iodine molecules. This absorption occurs because iodine has empty valence d orbitals which can be excited when they absorb certain wavelengths of visible light.

When iodine transitions from a lower to a higher energy state, the wavelength of light that it does not absorb is reflected. This unabsorbed light is what gives iodine its distinct purple color in its gaseous phase and when dissolved in certain solvents.