24.5+Color+and+Magnetism

__**24.5 - Color and Magnetism**__

This section applies information we have learned, namely the interaction of radiant energy with matter (producing **color**) and the property of **magnetism**, to transition-metal complexes to help us understand the model for metal-ligand bonding outlined in section 24.6 (Crystal-Field Theory).

__**Color-**__ The color of a complex is based upon
 * 1) The element
 * 2) Its oxidation state
 * 3) The ligands bound to the metal

In order for a compound to have color it must absorbs visible light (electromagnetic radiation with wavelengths from 400 to 700 nm). An equation we are already familiar with: shows the inverse relationship of the energy of electromagnetic radiation to its wavelength. An **absorption spectrum** is the amount of light absorbed as a function of wavelength.
 * E=hv = h(c/lambda)**

The visible radiation will only be absorbed by the compound if it has the energy required to move an electron from ground state to an excited state. This means that we can determine the color of a substance based off of what amount of radiation it absorbed using a handy color wheel.

Remember that the color we view on a object is the summation of the colors that were not reflected or transmitted by it. Also review, **complementary colors** are colors of the opposite hue that when mixed produce a neutral color (gray, white or black). So we see green when all of the colors but green are absorbed or when all of the colors except red strike our eyes. Therefore, there are two determinants as to why an object will portray a particular color:
 * 1) It transmits light of that color
 * 2) It absorbs light of the complementary color (determined by the color wheel)

__**Magnetism-**__ Many transition-metal complexes exhibit paramagnatism. There is an important distinction between paramagnetism and diamagnetism to take note of. Unpaired electrons are //attracted// into a magnetic field, called paramagnetism. Substances that do not have unpaired electrons are //repelled// a magnetic field.Using the **degree of paramagnetism** it is possible to determine the number of unpaired electrons per metal ion. In order for a complex to show color, it is necessary to have the presence of a partially filled d subshell. But there is a major distinction in the manner in which electrons are arranged in metal orbitals, leading to the creation of the Crystal-Field (Bonding) Theory.

Links: [|Transition Metal Complexes and Color] [|Video of Paramagnetism]

References:
 * 1) Brown, Theodore L., and H. Eugene LeMay. Chemistry: The Central Science. Upper Saddle River, NJ: Pearson Prentice Hall, 2008. Print.
 * 2) "D-block elements." Web. 20 Mar. 2011.<[]>
 * 3) "Paramagnetism: Compounds." University of Wisconsin. Web. 21 Mar. 2011. <[]>
 * 4) "Transition Metal Complexes and Color." Western Oregon University. 21 Mar. 2011. <[]>