 # Chapter 5 in your textbook pp. 117-141. Wave Nature of Light  In the early 1900s scientists observed that certain elements emitted visible light when.

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Chapter 5 in your textbook pp. 117-141

Wave Nature of Light  In the early 1900s scientists observed that certain elements emitted visible light when heated in a flame  Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electron’s in its atoms

Wave Nature of Light  For you to better understand the relationship and the nature of atomic structure, you need to understand the nature of light

Wave Nature of Light  Electromagnetic radiation  A form of energy that exhibits wavelike behavior as it travel through space  Visible light is a type of electromagnetic radiation  Examples include: visible light from the sun, microwaves, x-rays, radio waves

Waves  All waves can be described by several characteristics:  Wavelength  Frequency  Amplitude  Speed

Wave  Wavelength ( λ)  Shortest distance between equivalents points on a continuous wave  Measured from crest to crest or from through to through  Units: meters, centimeters, nanometers

Wave  Frequency (ν)  Number of waves that pass a given point per second  Unit: Hertz (Hz) = one wave per second (1/s) or (s -1 )  Example : 652 Hz = 652 waves/second=652/s = 652 s -1

Wave  Amplitude  Wave’s height from the origin to a crest, or from the origin to a trough

Wave  All electromagentic waves, including visible light, travel at a speed of 3.00 x 10 8 m/s  c = λν  c = speed of light, λ = wavelength, ν = frequency  The seed of light is the product of its wavelength and its frequency

Example  What is the wavelength of a microwave with a frequency of 3.44 x 10 9 Hz?  c = λν  λ = c / ν  λ = 3.00 x 10 8 m/s = 3.44 x 10 9 s-1 8.72 x 10 -2 m

Electromagnetic Spectrum  Although the speed of all electromagetic waves is the same, waves may have different wavelengths and frequencies  Wavelength and frequency are inversely related  As one quantity increase the other decrease

Electromagentic Spectrum  White light, such as sunlight, can be separated into a continuous spectrum of colors if passed through a prism  These are the colors of the rainbow (roy g biv) – red, orange, yellow, green, blue, indigo, violet)

Electromagnetic Spectrum  Electromagnetic spectrum (EM spectrum) is:  all forms of electromagnetic radiation  the only difference in the types of radiation is their wavelengths and frequencies  Each color has a different wavelength- Red has the longest wavelength and violet has the shortest wavelength

Electromagnetic Spectrum  Violet light has the greatest frequency and has more energy that the red light

Practice Problems  What is the frequency of green light, which has a wavelength of 4.90 x 10 -7 m?  An X-ray has a wavelength of 1.15 x 10 -10 m. What is its frequency?  What is the speed of an electromagetic wave that has a frequency of 7.8 x 10 6 Hz?  A popular radio station broadcasts with a frequency of 94.7 MHz. What is the wavelength of the broadcast? (1MHz = 10 6 Hz)

Why we care about spectroscopy?  Quantum concept: the temperature of an object is a measure of the average kinetic energy in particles.  Different forms of matter will emit and absorb light at characteristic wavelengths and frequencies

Spectroscopy  The study of how (and at what wavelengths) a sample emits and/or absorbs light is a way to:  Identify components in a sample (ex: elements & molecules)  Quantify concentration of these components  Identify types of bonds in a molecule

Emission Spectroscopy  Flame emission spectroscopy  Atoms absorb energy in a flame and then emit energy as light  The wavelengths of emitted light are characteristics to individual atoms  The intensity of emitted light is proportional to the element’s concentration

Emission Spectroscopy continued  The origin of this emission is the Decay, Relaxation, Excited of electrons from a high energy state to a more stable lower energy state  The wavelength of emitted light corresponds to the energy difference between these two states

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