CHEM+002+Lab+9+-+Nanoworld - Color My Nanoworld CHEM 002...

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Color My Nanoworld CHEM 002 – Laboratory 9 Goal This experiment introduces some of the properties of very small metal particles (nanoparticles). It also provides an introduction to the absorption of light by compounds and to the technique of absorption spectroscopy. Background Gold nanoparticles Nanoscience investigates the properties of materials that are larger than a single molecule but too small to resolve with an ordinary light microscope. These are objects whose size is in the range from a few nanometers to a few hundred nanometers (a nanometer, nm, is 10 -9 m). The physical and chemical properties are size-dependent over certain size ranges specific to the material and the property. By understanding these properties and learning how to utilize them, scientists and engineers can develop new types of sensors and devices. When a particle of gold metal is similar in size to wavelengths of visible light (400-750 nm), it interacts with light in interesting ways. The color of a gold nanoparticle solution depends on the size and shape of the nanoparticles. For example, while a large sample of gold, such as in jewelry, appears yellow, a solution of nanosized gold particles can appear to be a wide variety of colors depending on the size of the nanoparticles. In this laboratory you will explore these size- dependent properties of gold nanoparticles and investigate the effect of adding different substances. Absorption spectroscopy Light is characterized by its frequency, ν , or its wavelength, λ . Frequency and wavelength are related by the speed of light, c: c = νλ . Energy is transferred between light and matter in the form of photons, or quantized packets of energy; the energy of one photon is given by E = h ν = hc/ λ where h is Planck’s constant. A material can absorb light only if the energy of a photon of that wavelength corresponds to the energy difference between two of the quantum-mechanical energy levels of the material. Atoms have a small number of well-defined energy levels and they can absorb light of only a few well-defined wavelengths (line spectra). Large molecules, and particularly metal nanoparticles, have a very large number of energy levels, so they can absorb light over a broad band of wavelengths. A plot of the amount of light absorbed versus the frequency or wavelength of the light is called an absorption spectrum. When you look at a material in white light (sunlight or artificial room light), the color you see corresponds to the colors that are not absorbed much by the material. For example, chlorophyll, the pigment in
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This note was uploaded on 11/30/2011 for the course CHEM 002 taught by Professor Vidensik during the Spring '10 term at UC Merced.

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CHEM+002+Lab+9+-+Nanoworld - Color My Nanoworld CHEM 002...

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