• spectroscopy can be used to assess the purity of a substance

• spectroscopy can be used to identify unknown substances

• it is used in the parts of the electromagnetic spectrum

• principle : when substances are exposed to EM radiation many absorb wavelengths and transmit others.Different substances interact with the EM radiation in different was.each substance will produce its own absorbance or transmission spectra

• absorption

• different atoms absorb wavelengths of the EM spectrum.a spectrum with dark lines is produced that corresponds to the absorbed radiation

• the pattern of bands produced are distinctive for each element

• types of spectroscopy

  • emission

  • atoms emit energy as electromagnetic radiation

  • when electrons are excited to move into a higher energy level and they return the energy is released as light

  • the radiation can be detected and produces a spectrum with a series of bright lines that are distinctive for each element

  • all instruments is used for spectroscopy have the same basic construction

  • EM radiation source

  • monochromator for wavelength section

  • sample holder

  • detector

  • recording device

infrared spectroscopy

• infrared radiation has a longer wavelength than visible light 750nm to 1mm

• spectra can give information about structure and hence identify of organic compounds

• the covalent bonds in organic substances are not rigid but vibrate,bending and stanching at a unique frequency for each type of bond

• if IR radiation that falls on these bonds has the same frequency as that of the bonds that they are absorbed

• the energy from the IR rises the molecules into a higher energy level

• the amount of energy absorbed varies from bond to bond as does the frequency

• In and IR