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Chapter 5

Chapter 5. Electrons in Atoms. Wave Nature of Light. Electromagnetic radiation which is a form of energy that exhibits wavelike behavior as it travels through space. Examples: light, radio waves, x-rays, etc. Parts of a Wave. crest. wavelength. amplitude. origin. amplitude.

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Chapter 5

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  1. Chapter 5 Electrons in Atoms

  2. Wave Nature of Light • Electromagnetic radiation which is a form of energy that exhibits wavelike behavior as it travels through space. • Examples: light, radio waves, x-rays, etc

  3. Parts of a Wave crest wavelength amplitude origin amplitude wavelength trough

  4. Wavelength • Waves have a repetitive nature. • Wavelength- ( lambda) • shortest distance between corresponding points on adjacent waves. • Measured in units like meters, centimeters, or nanometers depending on the size. • 1 x 10-9 meters = 1 nanometer

  5. Frequency • # of waves that pass a given point per second. • Units are waves/sec, cycles/sec or Hertz (Hz) • Abbreviated n the Greek letter nu or by an f c = lf

  6. Frequency and wavelength • Are inversely related • As one goes up the other goes down. High frequency, Short Wavelength Low frequency, Long Wavelength

  7. Wave Formula • All electromagnetic waves, including visible light, travel at the speed of 3.00 x 10 8 m/s in a vacuum. • Speed of light = c = 3.00 x 108 m/s c=f Speed of light = (wavelength) x (frequency)

  8. Example Problem • What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz? Formula: c=f • = ? f = 3.44 x 109 Hz c = 3.00 x 108 m/s 3.00 x 108 m/s =  (3.44 x 109 s-1) 3.00E8 / 3.44E9 = 8.72 x 10-2 m

  9. Practice • What is the frequency of green light, which has a wavelength of 5.90 x 10-7m? • A popular radio station broadcast with a frequency of 94.7MHz, what is the wavelength of the broadcast? ( frequency needs to be is Hz)

  10. Different frequencies produce different types of waves. • The entire range of frequencies is called the electromagnetic spectrum • We are only able to see with our eyes a small portion of the spectrum = visible light • ROY G BIV • Different colors mean different frequencies/wavelengths

  11. Energy & The Spectrum • The energy of a wave increases with increasing frequency • High Frequency = High Energy • Low Frequency = Low Energy • Blue light has more energy than Red light

  12. High energy Low energy Low Frequency High Frequency X-Rays Radiowaves Microwaves Ultra-violet GammaRays Infrared . Long Wavelength Short Wavelength Visible Light

  13. Quanta • Max Planck suggested the idea of quanta or packets of energy. • Quanta is the minimum amount of energy that can be lost or gained by an atom. • Energy is quantized = it comes in packets (like stairs or pennies only whole numbers)

  14. Planck’s Constant • h = 6.626 x 10-34 J.s (Joule seconds) Energy = (Planck’s constant)(frequency) E = hf Example: What is the energy in Joules of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014 Hz? E = ? h = 6.626 x 10-34Js f = 7.23 x 1014 Hz (or s-1) E = (6.626 x 10-34Js)(7.23 x 1014 s-1) E = 4.79 x 10-19 J

  15. Photoelectric Effect • In the 1900s, scientist studied interactions of light and matter. • One experiment involved the photoelectric effect, which refers to the emission of electrons from a metal when light shines on the metal. • This involved the frequency of the light. It was found that light was a form of energy that could knock an electron loose from a metal.

  16. Photon • Light waves can also be thought of as streams of particle. • Einstein called these particles photons (He won a Nobel Prize for this) • A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum energy.

  17. Bohr’s Model • Why don’t electrons fall into nucleus? • Bohr suggested that they move like planets around sun. • Certain amounts of energy separate one level from another.

  18. Nucleus is found inside a blurry “electron cloud”

  19. Bohr’s Model Nucleus Electron Orbit Energy Levels

  20. Bohr’s Model } • Further away from nucleus means more energy. • There is no “in between” energy • Energy Levels Fifth Fourth Third Increasing energy Second First Nucleus

  21. Bohr Model of the Atom • Ground state- the lowest energy state of an atom. • Excited state – state in which an atom has a higher potential energy than its ground state. • Energy is quantized. It comes in chunks. • quanta - amount of energy needed to move from one energy level to another. • Since energy of an atom is never “in between” there must be a quantum leap in energy.

  22. Bohr Energy Levels • K = 2 electrons – 1st • L = 8 electrons – 2nd • M = 18 electrons – 3rd • N = 32 electrons – 4th

  23. Heisenberg Uncertainty Principle • This is the theory that states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

  24. Quantum Theory • Schrodinger derived an equation that described energy & position of electrons in atom • Schrodinger along with other scientists laid the foundation for the modern quantum theory, which describes mathematically the wave properties of electrons and other very small particles.

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