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Unformatted text preview: 3-1 Ch. 3 Atomic Spectra of Atoms and IonsObjective To understand the principles of atomic spectra and flame ionization To observe and record the line spectra for several elements, molecules and ions To understand the correlation between emission spectra and atomic structure IntroductionChemists struggled over several decades to understand what comprises the atom. We now know that the atom consists of a nucleus that contains protons and neutrons and electrons that reside some distance from the nucleus. Our understanding of where electrons reside in an atom and the energy of those electrons come from obtaining emission and absorption spectra. When atoms or ions absorb energy from an outside source they can release this energy in the form of light or radiant energy. This radiant energy is described by two fundamental variables, wavelength () and frequency (). These two variables are related through a simple relationship: c(1)where cis the speed of radiant energy in a vacuum, 3.0 x 108meters per second (units = m/s). Most commonly, wavelength is described in units of either meters or nm (109m). Frequency is given in units of cycles per second (s1), which is also called Hertz (Hz). Radiation refers to any form of energythat travels in all directions from a single source, such as light from the sun. Radiation exists in many different forms, many of which should be familiar to you: X-rays, ultraviolet, visible, microwave, radio, etc. Figure 1 relates the wavelength and frequencies for several types of radiation; you should notice that wavelength and frequency are inversely related as expected from equation 1. Various forms of radiation have different energies; you may know that ultra-violet light can cause a sunburn and X-rays can result in tissue damage. The formula that relates the energy of radiation (E) to the frequency () of radiation is: hE(2)Atomic Spectra3-2 where his a constant called Plancks constant (6.626 x 1034Js), named after Max Planck who first observed this relationship. Equations 1and 2allow you to interconvert between wavelength, frequency and energy of radiation. Energy Decreasing Wavelength Increasing = 10141010108107105102102(m) Gamma ray X-ray Ultraviolet Visible Infrared Microwave Radio waves = 102210181016101510131010108(s1) Frequency Increasing Energy Increasing Figure 1: Electromagnetic Spectrum Radiation may be composed of one wavelength of light (monochromatic light) or several wavelengths (polychromatic light). A laser pointer is an example of a source that emits radiation of only one wavelength. You may be familiar with white light being the combination of all the colors of visible light. White light can be separated into its component wavelengths by passing it through a prism, resulting in a rainbow. While passing through the prism each wavelength of light is bent differently due to its unique wavelength, allowing one to see each wavelength...
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This note was uploaded on 01/17/2012 for the course S 117 taught by Professor Stephenjacobson during the Fall '11 term at Indiana.
- Fall '11