Jump to content

Formation of Ion Color


Recommended Posts

As we know, some metal ions like Calcium ion , potassium ion and sodium ion are colorless, while Cobalt ion, Iron(II)/(III) ion have color. Why ? What is the physical nature beneath that phenomenon ? What theories are involved ?


As Ilja has already said it sbecause the wavelengths of light the ions absorb varies, even the colourless ones absorb light but its notmally somewhere in the infrared spectrum :)


Have a look on Wikipedia or Google for more informaiton on this subject :D




Ryan Jones

Link to comment
Share on other sites

Most of the time, the color of complex ions comes from d->d transitions. That is, the absorbtion of a specific wavelenght of light excites electrons in one d orbital (e.g. from the t2g orbitals to the eg* orbitals). Calcium, potassium, and sodium are all in the first two columns of the periodic table and therefore, their valence electrons are only in the s orbital. Transition metals like cobalt, iron, and manganese have d electrons and therefore can have d->d transitions. It is also worth noting that despite the fact that zinc is a transition metal, Zn2+ ions are generally colorless because they have a full d subshell, so no d->d transitions can occur.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.