chapter 24

• is a form of energy that is transmitted through space at

  enormous velocities.

  Electromagnetic radiation
• one of the most renowned scientists of the twentieth century. He was awarded the Nobel Prize in Physics in 1965 for his role in the development of quantum electrodynamics.

  Richard P. Feynman
• electromagnetic radiation can be treated as discrete packets of energy or particles called

  photons or quanta.
• energy of a photon is directly proportional to its frequency
• the direction in which the field oscillates is perpendicular to the direction in which the radiation propagates.
• The _____ of an electromagnetic wave is a vector quantity that

  provides a measure of the electric or magnetic field strength at a maximum in the wave.

  amplitude
• The _______ of an electromagnetic wave is the time in seconds for

  successive maxima or minima to pass a point in space.

  period
• The _____ of an electromagnetic wave is the number of oscillations that occur in one second.

  frequency
• The unit of frequency is the ____, which corresponds to .

  hertz (Hz) ; one cycle per second (1 Hz = 1 s^-1_
• the _____ of the wave front through a medium depends on both the medium and the frequency.

  velocity (v)
• The _____ is the linear distance between successive

  maxima or minima of a wave,

  wavelength
• This velocity, which is given the special symbol c,
• This velocity, which is given the special symbol c, 


  2.99792 x10^8 m s^-1.
• The ______ of a medium measures the extent of interaction between electromagnetic radiation and the medium through which it passes. 


  refractive index, h
• The _____ is another way to describe electromagnetic radiation. It is defined as the number of waves per centimeter and is equal to 1/l. 


  wavenumber, n,
• The _______, in watts (W) is the energy of a beam that reaches a given area per unit time.

  radiant power, P
• The _____ is the radiant power-per-unit solid angle.

  intensity
• The wavenumber in cm^-1 (Kayser) is most often used to describe radiation in the infrared region.
• Wavelength is inversely proportional to energy.
• wavenumber and frequency in contrast to the wavelength are directly proportional to the photon energy.
• a particle of electromagnetic radiation having zero mass and

  an energy of hv.

  photon
• UV wavelength 


  180-380 nm
• Visible light wavelength


  380-780 nm
• Near-IR wavelength 


  0.78-2.5 micrometer
• Mid-IR wavelength


  2.5 - 50 micrometer
• The visible region of the spectrum extends from about 400 nm to almost

  800 nm
• low-energy radiation used in _______________ causes subtle changes, such as changes in spin


  nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy
• are spectroscopic methods based on ultraviolet, visible, and infrared radiation.

  Optical methods
• usually refers to methods in which the stimulus is heat or electrical energy,

  emission spectroscopy
• refers to excitation of the analyte by a chemical reaction.

  chemiluminescence spectroscopy
• In the firefly reaction, an enzyme luciferase catalyzes the oxidative

  phosphorylation reaction of luciferin with adenosine triphosphate (ATP) to produce oxyluciferin, carbon dioxide, adenosine monophosphate (AMP), and light.
• The results of such a measurement are often expressed graphically by a ______, which is a plot of the emitted radiation as a function of frequency or wavelength.


  spectrum
• we measure the amount of light absorbed

  as a function of wavelength.

  absorption spectroscopy
• means to decrease the energy per unit area of

  a beam of radiation.

  attenuate
• tells us quantitatively how the amount of attenuation depends on the concentration of the absorbing molecules and the path length over which absorption occurs
• Similarly, for a given path length of light, the higher the concentration of absorbers, the stronger the attenuation.
• The term ______

  refers to radiation of a single color;

  that is, a single wavelength or

  frequency.

  monochromatic radiation
• is often expressed as a percentage and called the per-

  cent transmittance.

  Transmittance
• The _________ of a solution is related to the transmittance in a logarithmic manner

  absorbance (A)
• absorbance is directly proportional to the concentration

  of the absorbing species, c, and to the path length, b, of the absorbing medium as

  beer's law