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Electrons in Atoms

Electrons in Atoms. Light Energy. Rutherford’s model -Shows where protons & neutrons are -Not good at showing the location of electrons . Light Energy. When elements are heated, they are excited & jump up to a higher energy level. In doing so, they give off a color of light.

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Electrons in Atoms

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  1. Electrons in Atoms

  2. Light Energy • Rutherford’s model -Shows where protons & neutrons are -Not good at showing the location of electrons

  3. Light Energy • When elements are heated, they are excited & jump up to a higher energy level. In doing so, they give off a color of light. • Each element gives off a unique color called its atomic emission spectrum. • The electrons are what give each element their unique color. • Light gives us a clue to how electrons are arranged. • Light behaves like a wave & like a particle.

  4. Light Energy • Light in wave form is called an electromagnetic wave, & is part of the electromagnetic spectrum which includes x-rays, TV waves, microwaves, radio waves, UV waves & gamma waves.

  5. Wave Structure Trough – low points Crest – high points Amplitude – max displacement from equilibrium (middle of wave). Wavelength – the shortest distance between points in which a wave repeats itself. (crest to crest or trough to trough) symbol - λ crest

  6. Parts of a Wave length • Wavelength - of one wave, from a crest to a crest or trough to a trough • Symbol = λ () • Measured in lambda meters • Frequency- number of waves that pass a point in 1 second • symbol = v() • Measured in (Hz) nu Hertz

  7. Calculations • All EM radiation travels at the speed of light, c = 3.00 x 108 m/s in the vacuum of space • Formula: c = λ v c is constant speed of light v is frequency λ is wavelength

  8. Microwaves are used to transmit information. What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz? Known v= 3.44 x 109 Hz c = 3.00 x 108 m/s Unknown λ= ? m c = λv λ= c/v

  9. λ= 3.00x 108/ 3.44 x 109 • Answer: 8.72 x 10-2m What is the frequency of green light, which has a wavelength of 4.90 x 10-7m An X ray has a wavelength of 1.15 x 10-10m. What is the frequency?

  10. Light Particles • Light is like a particle because there are only certain amounts of energy it can have. • Light as a particle is called a photon. • The minimum amount of energy a photon can have is called a quantum.

  11. Light Particles • Max Planck found that this energy could be calculated with the formula E = h ν • E is energy, measured in Joules (J) • h is Planck’s Constant = 6.626 x 10-34 Js • v is frequency (Hz or 1/s) • Once the minimum amount of energy is calculated, the actual energy can be a multiple of the quantum amount. (1x E, or 2 x E, or 3 x E....)

  12. Water drops in the air disperse the white light of the sun into a rainbow. What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014Hz? Known v = 7.23 x 1014 s-1 h = 6.626 x 10-34 J s Unknown Ephoton= ? J Ephoton= (6.626 x 10-34J s)(7.23 x 1014 s-1)

  13. Cancel the units • Answer: 4.79 x 10-19J What is the energy of each of the following types of radiation? • 6.32 x 1020s-1 • 9.50 x 10 13 Hz • 1.05 x 10 16 s-1

  14. Photoelectric Effect • Electrons (called photoelectrons) are emitted from a metal’s surface when light of a certain frequency shines on the surface. • Example: calculators. • Photoelectric cells convert light into electric energy

  15. Bohr Model • Niels Bohr in 1913 proposed a quantum model for the hydrogen atom which correctly predicted the frequencies of the lines (colors) in hydrogen’s atomic emissions spectrum.

  16. Bohr Model • His model gave atoms only certain allowable energy states. • The lowest state is called the ground state. • When an atom gains energy it is said to be in an excited state.

  17. Bohr Model • Bohr also said that the motion of the electron relates to its energy state. That electrons move around the nucleus in certain allowed circular orbits. • The smaller the orbit, the lower the energy state.

  18. Bohr Model • Bohr assigned each energy level a quantum number, n. • There are only 7 energy states.

  19. Bohr Model • The 7 energy states are like rungs on a ladder, electrons can move up or down the ladder from rung to rung, but there is no “in between”. • An electron can only move from one allowable orbit to another and can only emit or absorb certain amounts of energy.

  20. Bohr Model The 1st energy level can hold only 2 e-, 2nd 8e-, 3rd 8e-, 4th 18e-, 5th 18e-, 6th 32e- remember these #’s 2-8-8-18-18-32! e- e- e- Ex: Draw the Bohr model for Fluorine e- e- e- e- nucleus # of Protons = 9 e- # of neutrons = 10 e- # of Electrons = 9

  21. Draw the Bohr Model for Ni • # of e- = 28 1st level = 2e- e- e- 2nd level = 8e- e- e- e- 3rd level = 8e- e- e- e- e- e- 4th level = 10e- e- e- e- e- e- e- e- e- nucleus e- e- e- e- e- e- e- e- e- e-

  22. Draw the Bohr model for the following elements: Co F Br Ag

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