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Electrons in atoms

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

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Electrons in atoms

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  1. Chapter 5 in your textbook pp. 117-141 Electrons in atoms

  2. 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

  3. 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

  4. 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

  5. Waves • All waves can be described by several characteristics: • Wavelength • Frequency • Amplitude • Speed

  6. 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

  7. 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

  8. Wave • Amplitude • Wave’s height from the origin to a crest, or from the origin to a trough

  9. Wave • All electromagentic waves, including visible light, travel at a speed of 3.00 x 108m/s • c = λν • c = speed of light, λ = wavelength, ν = frequency • The seed of light is the product of its wavelength and its frequency

  10. Example • What is the wavelength of a microwave with a frequency of 3.44 x 109 Hz? • c = λν λ = c / ν • λ = 3.00 x 108 m/s = 3.44 x 109 s-1 8.72 x 10-2 m

  11. 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

  12. 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)

  13. 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

  14. Electromagnetic Spectrum • Violet light has the greatest frequency and has more energy that the red light

  15. 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 10-10m. What is its frequency? • What is the speed of an electromagetic wave that has a frequency of 7.8 x 106 Hz? • A popular radio station broadcasts with a frequency of 94.7 MHz. What is the wavelength of the broadcast? (1MHz = 106 Hz)

  16. 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

  17. 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

  18. 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

  19. 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

  20. Question??

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