For example, the line spectra shown below for the elements helium and carbon are clearly quite different. The result is called a line emission spectrum, and can serve as a ‘fingerprint’ of the element to which the atoms belong. If emitted photons are in the visible region of the spectrum, they may be perceived as lines of different colors (note that photons outside the visible spectrum may also be emitted, but cannot be seen by eye). The spacing between energy levels in an atom determines the sizes of the transitions that occur, and thus the energy and wavelengths of the collection of photons emitted: However, when electrons subsequently return from higher energy levels to lower energy levels, energy is released predominantly in the form of electromagnetic radiation. The energy absorbed could be in the form of heat (as in flame tests), or electrical energy, or electromagnetic radiation. So, how does electromagnetic radiation relate to flame tests? Well, when an atom (or ion) absorbs energy, its electrons can make transitions from lower energy levels to higher energy levels. Other examples of electromagnetic radiation include X-rays, ultraviolet light, infrared light, microwaves and radio waves. Differences in the wavelengths of visible light are manifested as different colors, shown in the Color Spectrum below (colors can be seen in the PDF document on-line). Visible light is the most familiar example of electromagnetic radiation.
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