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5.3 Notes Light & Spectrometry Pg. 136-149
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Objectives Appreciate the phenomenon of how an atom absorbs and releases energy in the form of light Understand the differences between wave and particle theories of light Describe the electromagnetic spectrum Understand and explain the dispersion of light through a prism
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Theory of Light Color is a visual indication of the fact that objects absorb certain portions of visible light and transmit or reflect others. Different chemical substances absorb certain types and certain amounts of light.
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Two Models for Explaining Light 1. Light described as a continuous wave 2. Light described as a stream of discrete energy particles
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Light as a continuous wave c = λ x f Wavelength ( λ - lambda) Unit of measure = nanometer Frequency (f) refers to the speed at which wavelengths pass a given point in a unit of time Cycles per second Speed of light is 300 million meters per second (c)
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Light Visible light is identified by the electromagnetic spectrum Distinguishable by wavelength and frequencies. Can be described as continuous as long as it travels space
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LASER Light Amplification by the Simulated Emission of Radiation Coherent light Light that has all its waves pulsating in unison
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Light as a stream of discrete particles Occurs when radiation is absorbed by a substance Discrete particles are known as photons each with a definite amount of energy E = hf (E energy, f is frequency) h = Planck ’ s constant 6.6262 x 10 -34 J/s
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Spectrophotometry Measure the quantity of radiation that a particular material absorbs as a function of wavelength or frequency The invisible radiations of the electromagnetic spectrum. This absorption by chemical substances is selective because different materials have different energy requirements and therefore absorb at different frequencies
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Spectrophotometer An instrument that measure absorption spectrum of a chemical substance Produces a graph that shows the absorption of UV, visible, and IR radiations
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Some radiation reflected so not all is absorbed Just how much is absorbed depends on the concentration of the absorbing substance Used to obtain qualitative data.
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In-Class Assignment/Homework
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