Chemists today, like alchemists of past ages, use color to identify and quantify substances. This technology that uses light as an analytical tool extends far beyond the alchemist s wildest dreams. The visible range of light, color, is only a small portion of the electromagnetic spectrum. We can now use more portions of the electromagnetic spectrum than the visible range. In fact we can use ultraviolet light, visible light, and infrared light portions of the electromagnetic spectrum to characterize substances.
New instruments exist that use light to determine the number and types of molecules in a sample.
These instruments are called spectrometers. We can build spectrometers to monitor the chemistry of literally thousands of chemicals processed here on earth. These instruments probe distant planets to determine the type and amount of substances that exist there. The elements in distant stars can even be determined using spectrometers. All of this capability is based upon some relatively simple relationships between the amount of substance present and the amount of light emitted or absorbed at a particular wavelength.