Assignment... I chose Mercury (Hg) Choose one of the transition or inner transit

Question

Assignment... I chose Mercury (Hg) Choose one of the transition or inner transition metals from the periodic table. Using your book (Chapter 23 may be very useful) and Internet resources, discuss why your transition metal and their compounds display a variety of color. Be sure to include in your discussion, important oxidation states, the electron configuration and how the d-electrons are involved. How can you include the electromagnetic spectrum and the nature of light into your discussion? How is energy and wavelength related? Use your knowledge of the emission and absorption of light in your discussion. Remember to site your sources in APA style.

Explanation / Answer

Hg is colorless. We must take another transition element like, say, Co. Cobalt compounds display a variety of colors like :

Co(H2O)62+ is pink

CoCl2(H2O)2 is blue

[CoF6]3- is green

[Co(NH3)]63+ is yellow-orange

The d-orbitals of a free transition metal atom or ion are degenerate (all have the same energy.) However, when complexes are formed the d-orbitals of the metal interact with the electron cloud of the ligands in such a manner that the d-orbitals become non-degenerate (not all having the same energy.) Some ligands only produce a small energy separation among the d-orbitals while others cause a wider band gap. Different values of energy gaps correspond to different wavelenths of light absorbed and hence, different colors of different complexes.

For Co, configuration is 3d7 4s2 and it commonly shows +2/+3 oxidation states with 3d7 and 3d6 configurations. This causes difference in splitting pattern of d-electrons and different possibilities of electronic excitation leading to different colors in presence of different ligands.

When the d-level is not completely filled, it is possible to promote and electron from a lower energy d-orbital to a higher energy d-orbital by absorption of a photon of electromagnetic radiation having an appropriate energy. Electromagnetic radiations in the visible region of the spectrum often possess the appropriate energy for such transitions.

Although visible light appears "white", it is made up of a series of colors. White light consists of three primary colors (red, yellow and blue). These primary colors can be mixed to make three secondary colors (orange, green and violet).The violet end with the maximum energy and minimum wavelenth and the red end with minimum energy and maximum wavelenght (wavelenth is inversely proportional to energy).
When light passes through a solution containing transition metal complexes, we see those wavelengths of light that are transmitted. It is the complementary color of the color absorbed that is perceived by our eyes.

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