COLOUR OF VARIOUS SUBSTANCES!!!

[Harish Kumar.A]

Hello friends,

 

I have been thinking that when chemical reaction take place sometimes colour change may happen as new substance are formed.So what in atomic level decide the color of substance.Does the color of substance are decided by electron,proton or any other atomic particles.If these particles really does decide color,then how???

[Klaynos]

Hello friends,

 

I have been thinking that when chemical reaction take place sometimes colour change may happen as new substance are formed.So what in atomic level decide the color of substance.Does the color of substance are decided by electron,proton or any other atomic particles.If these particles really does decide color,then how???

 

To a first order approximation it is how light of different wavelengths interacts with the electrons of the material. This is (for non-magnetic materials) quantified by the permittivity of the material. Depending on the material there are a number of different ways to model this. For the most part these model the electrons being driven by the electric field and other similar interactions. A good place to start is probably the Drude model.

[juanrga]

Hello friends,

 

I have been thinking that when chemical reaction take place sometimes colour change may happen as new substance are formed.So what in atomic level decide the color of substance.Does the color of substance are decided by electron,proton or any other atomic particles.If these particles really does decide color,then how???

 

The electronic structure of substance defines its visual properties when the difference between energy levels is in the range of visible spectrum. The substance absorbs certain wavelengths of white light, and we see what is left over. The particular wavelengths of light that a given substance absorbs determine the colour we perceive.

 

Chemists are able to predict the colour of a substance before synthesizing it. The most simple quantum model to predict colour is the particle-in-a-box model.

Edited June 2, 2012 by juanrga

[Klaynos]

There are some reactions that result in certain crystalline forms. Then you can get colours which do not depend on transition energies at all.

 

http://www.viewsfromscience.com/documents/webpages/natural_photonics_p1.html

 

What I'm trying to say I guess is that it's not always as simple as energy levels.

[lucifer]

there is property of transisiton elements(d-block elements) called flourosence....the electrons in the d-orbital absorb a amount of energy from white light and excites to higher state...there due to unstability come back to original energy level thus realsing energy....here actually eletron releases colour complimentary to colour obsorbed from white light

heres a colour wheel which shows the complimentry colour:http://www.chemguide.co.uk/inorganic/complexions/colourwheel.gif

Edited June 3, 2012 by lucifer

[John Cuthber]

there is property of transisiton elements(d-block elements) called flourosence....the electrons in the d-orbital absorb a amount of energy from white light and excites to higher state...there due to unstability come back to original energy level thus realsing energy....here actually eletron releases colour complimentary to colour obsorbed from white light

heres a colour wheel which shows the complimentry colour:http://www.chemguide.co.uk/inorganic/complexions/colourwheel.gif

With the rather odd exception of fluorescence of rubies, can you actually cite an example of d block elements fluorescing in conditions outside of a lab?

[mississippichem]

There are some reactions that result in certain crystalline forms. Then you can get colours which do not depend on transition energies at all.

 

http://www.viewsfromscience.com/documents/webpages/natural_photonics_p1.html

 

What I'm trying to say I guess is that it's not always as simple as energy levels.

 

I agree

 

There are even a few examplea of compunds vibrational energy levels making a non-negligible contribution to its observed "color".

 

The particle in a box method of predicting color only works for compounds where the pi antibonding orbital is the most populated excited state and things like refractivity and specular reflection aren't significant. For example linear conjugated polyenes.

 

For metallic complexes d-orbitals and high symmetry force us to switch over to ligand field theory which gets messy.

 

Bring in high paramagnetism ans you'll have serious spin considerations to deal with.

Edited June 3, 2012 by mississippichem

[juanrga]

The particle in a box method of predicting color only works for compounds where the pi antibonding orbital is the most populated excited state and things like refractivity and specular reflection aren't significant. For example linear conjugated polyenes.

 

When I alluded to the particle in a box model I only said was the simplest possible quantum model, not that was complete or always valid. Even for linear conjugated polyenes this model of electronic structure is a crude one.

Edited June 3, 2012 by juanrga

[mississippichem]

When I alluded to the particle in a box model I only said was the simplest possible quantum model, not that was complete or always valid. Even for linear conjugated polyenes the model is a crude one.

 

I know. I was merely discussing further. Not trying to rob you of credintials. You may very well know better than I. I don't know you personally.