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The Bohr Atom Evolution of Electron Configuration

The Bohr Atom Evolution of Electron Configuration. Learning about the Electron. Technicians, engineers and scientists, know a lot about electrons today because of a three pronged cyclic learning process. > Conduct experiments (observations) to explore a phenomena. .

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The Bohr Atom Evolution of Electron Configuration

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  1. The Bohr Atom Evolution of Electron Configuration

  2. Learning about the Electron Technicians, engineers and scientists, know a lot about electrons today because of a three pronged cyclic learning process. > Conduct experiments (observations) to explore a phenomena. Observations Model > Develop a story (theory) to predict what will happen in the next experiment. > Find equations (i.e., models) that explain and support the theory. Theory This repetitive process continues as the knowledge base increases.

  3. Learning about the Electron Aristotle’s “Composition of the Universe” Theory (354 BC) All things are composed of earth, air, fire, and water with no concept of an electron. Dalton’s “Atomic” Theory (1808) Tiny indivisible particles that have no sub-particle sized parts. J. J. Thomson’s “Plum Pudding” Model (1898) Sub-particle sized parts exist in an atom but no idea of their arrangement. Ernest Rutherford’s “Nucleus” Model (1909) Electrons are independent sub-particle sized parts occupying their own specific space.

  4. Learning about the Electron Summary of Bohr’s (Planetary) Model (1913) Electrons orbit the nucleus in different orbits at different fixed distances. Electrons that leave one orbit must move to another orbit. Electrons only change orbits if specific amounts (quanta) of extra energy from the outside world are involved. Electrons that receive enough extra energy from the outside world can leave the atom they are in. Electrons that return to orbits they used to reside in give up the extra energy they acquired when they moved in the first place. Electronic energy given up when electrons move back into an original orbit often emit a specific color light.

  5. Observations Model Theory The Puzzle Pieces Bohr had to Solve Observations The most important observation Bohr needed to explain was the fact that when energy was added to atoms the atoms gave off (emitted) light. Theory The biggest problem with Rutherford’s story was why the electrons don’t eventually crash into the nucleus and destroy the atom. Model Up to this point in time (1913), nobody knew why Balmer’s equation predicted the color (frequency) of the light waves emitted by atoms. A difficult puzzle to solve, but Bohr made a major step in putting the pieces together.

  6. The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. Thermal Emission (Max Plank 1900) > A hot solid will emit light. > A solid glows red at 750 degrees centigrade. > A solid glows white as the temperature increases to 1200 degrees centigrade. As the temperature increases from 750 degrees, more yellow and blue light is emitted and mixes with the red light to give white light.

  7. Photoelectric Effect Light Source Photons The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. When an element is subjected to heat,light, or electrical discharge, it can, under certain conditions, give off light. Photoelectric Effect Albert Einstein (1905) (Nobel prize 1921) Light (photons) can force electrons to be emitted from the surface of a metal.

  8. The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. When an element is subjected to heat, light, orelectrical discharge, it can, under certain conditions, give off light. Corona Who, What, Where is it? Who St. Elmo’s Fire As described in “The Tempest” What/Where

  9. “I boarded the king’s ship; now in the beak, Now in the waist, the deck, in every cabin, I flamed amazement; sometimes I’d divide And burn in many places; on the topmast, The yards and bowsprit, would I flame distinctly, Then meet and join.” The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, orelectrical discharge, it can, under certain conditions, give off light. Corona (1611) A passage from “The Tempest” by William Shakespeare

  10. The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. Bohr’s postulates include the belief that Orbit number 3 (n = 3) electrons are in orbits but the orbits are at different distances from the nucleus. Orbit number 1 (n = 1) Ernest Rutherford’s Model (1909) electrons that leave one orbit must move to another orbit.

  11. 12 C 6 The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. Bohr’s concept of a carbon atom with a “ground” state electron configuration. 2 electrons in orbit number 3 2 electrons in orbit number 1 2 electrons in orbit number 2 remember an atom that has 6 protons is always called a carbon atom Atom with 6 protons and 6 electrons “Ground” state electron configuration

  12. 12 C 6 The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. The electron configuration of an atom changes when energy (heat, light, or electricity) is added to the atom. electrons only change orbits if specific amounts (quanta) of extra energy from the outside world are involved. Atom with 6 protons and 6 electrons “Ground” state electron configuration “Excited” state electron configuration

  13. Observations 12 C 6 The Puzzle Pieces Bohr had to Solve Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. Energy is removed from the atom when an electron returns to its original orbit. Atom with 6 protons and 6 electrons “Excited” state electron configuration “Ground” state electron configuration

  14. this electron used to be in orbit #2 “Excited” state electron configuration “Higher” energy state for an atom 12 C 6 The Puzzle Pieces Bohr had to Solve Observations Observations add energy “Ground” state electron configuration “Lower” energy state for an atom electrons only change orbits if specific amounts (quanta) of extra energy from the outside world are involved.

  15. “Ground” state electron configuration “Lower” energy state for an atom 12 C 6 The Puzzle Pieces Bohr had to Solve Observations Observations this electron has returned to orbit #2 release energy “Excited” state electron configuration “Higher” energy state for an atom When an electron returns to an orbit it use to be in it will always give up a quanta of energy. Often this energy is put back into the world as a photon of colored light. electrons only change orbits if specific amounts (quanta) of extra energy from the outside world are involved.

  16. Photoelectric Effect Light Source Photons 14 N 7 The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. “Ground” state electron configuration Sometimes, the amount of energy that is taken up by the atom is the exact amount that will let an electron in the atom’s outer orbit actually leave the atom.

  17. positive electrode negative electrode The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, When an element is subjected to heat, light, or electrical discharge, When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. If atoms are located in an electric field, The electrons can get the exact energy they need from the field to move to an outer orbit. When electrons give up that energy and return to their original orbits, light is emitted. Corona and Plasma Discharges

  18. positive electrode negative electrode The Puzzle Pieces Bohr had to Solve Observations Observations When an element is subjected to heat, light, or electrical discharge, it can, under certain conditions, give off light. Helium corona and plasma discharge

  19. Observations Model Theory Theory The Puzzle Pieces Bohr had to Solve Theory The biggest problem with Rutherford’s story was why the electrons do not eventually crash into the nucleus and destroy the atom. Bohr’s postulates include the belief that Electrons can only have a specific energy value to be in a specific orbit of an atom. Electrons remain in a specific orbit unless they obtain additional energy to move into orbits that are further from the nucleus. Therefore, electrons are not satellites (Rutherford’s theory) like man made satellites in continuous decaying orbits that gradually spiral toward the center.

  20. Theory Each electron in orbit number 1 has 2.18 x 10 -18 Joules of energy The Puzzle Pieces Bohr had to Solve Theory The biggest problem with Rutherford’s story was why the “satellite” electrons don’t eventually crash into the nucleus and destroy the atom. Bohr’s Energy Level Postulates: Orbit number 1 is the orbit closest to the nucleus. (This is a tiny amount of energy, but remember that an atom is a tiny thing in the first place.)

  21. Theory -18 -18 -18 0.55 x 10 2.18 x 10 0.24 x 10 Joules Joules Joules The Puzzle Pieces Bohr had to Solve Theory The biggest problem with Rutherford’s story was why the “satellite” electrons don’t eventually crash into the nucleus and destroy the atom. The energy of an electron orbit is inversely proportional to the square of the orbit number. Orbit number Energy electron needs 1 2 3

  22. Model Observations Model Theory -18 -18 2.18 x 10 2.18 x 10 2 (orbit number) 2 (n) The Puzzle Pieces Bohr had to Solve Model Up to this point in time, nobody knew why Balmer’s equation predicted the color (frequency) of the light waves emitted by atoms. Bohr’s Energy Level Equation Postulate The energy of an electron orbit is inversely related to the square of the orbit number. The energy of an electron orbit isinversely relatedto thesquareof the orbit number. electron energy level equals Joules Joules = E

  23. Model Joules = E -18 n 2.18 x 10 -18 2.18 x 10 Joules -18 -18 2.18 x 10 2.18 x 10 E = 2 1 (n) (n) (1) (1) (n) The Puzzle Pieces Bohr had to Solve Model Up to this point in time, nobody knew why Balmer’s equation predicted the color (frequency) of the light waves emitted by atoms. Bohr’s Energy Level Equation Postulate The Bohr model for calculating the energy relative to an atomic orbital. The Bohr model calculated energy for orbit the closest to nucleus. n =1 = =

  24. Model Joules = E -18 n 2.18 x 10 -18 0.55 x 10 Joules -18 -18 2.18 x 10 2.18 x 10 E = 2 2 4 (n) The Puzzle Pieces Bohr had to Solve Model Up to this point in time, nobody knew why Balmer’s equation predicted the color (frequency) of the light waves emitted by atoms. The Bohr model for calculating the energy relative to an atomic orbital. The Bohr model calculated energy for second (n=2) orbit. n =2 = = (2) (2)

  25. Model Joules = E -18 n 2.18 x 10 -18 0.24 x 10 Joules -18 -18 2.18 x 10 2.18 x 10 E = 2 3 9 (n) The Puzzle Pieces Bohr had to Solve Model Up to this point in time, nobody knew why Balmer’s equation predicted the color (frequency) of the light waves emitted by atoms. The Bohr model for calculating the energy relative to an atomic orbital. The Bohr model calculated energy for third (n=3) orbit. n =3 = = (3) (3)

  26. Model = = (3) (3) -18 -18 -18 0.55 x 10 0.24 x 10 0.14 x 10 Joules Joules Joules -18 -18 -18 -18 -18 = = 2.18 x 10 2.18 x 10 2.18 x 10 2.18 x 10 2.18 x 10 (2) (2) E E E = = = 3 2 4 9 4 16 The Puzzle Pieces Bohr had to Solve Model The Bohr model energy calculation for the: second (n=2) orbit, third (n=3) orbit, and the fourth (n=4) orbit. =

  27. Model -18 0.55 x 10 -18 0.14 x 10 -18 -18 0.55 x 10 0.14 x 10 Joules Joules -18 -18 -18 = = 2.18 x 10 2.18 x 10 2.18 x 10 (2) (2) -18 -18 E E = = 0.55 x 10 Joules 0.14 x 10 Joules 4 2 4 -18 0.14 x 10 -18 16 0.55 x 10 The Puzzle Pieces Bohr had to Solve Model The Bohr model energy calculation for second (n=2) orbit. fourth (n=4) orbit = energy difference for electron transitions between second and fourth orbits. = E2–E4 = -

  28. Model -18 -18 0.41 x 10 0.41 x 10 If Niels Bohr were alive today, he would say that when an electron moves from the fourth orbit of an atom to the second orbit of the same atom, then Joules of energy will be released. The Puzzle Pieces Bohr had to Solve Model energy difference for electron transitions between second and fourth orbits. -18 -18 [ ] = 0.55 x 10 - 0.14 x 10 Joules Joules energy difference =

  29. Model Joules Niels Bohr believed that of energy -18 0.41 x 10 The Puzzle Pieces Bohr had to Solve Model would be released when an electron went from orbit 4 to orbit 2 in an atom. Now he just had to convince the rest of the world that what he believed was what really happened. How do you think he did that?

  30. Model Joules Niels Bohr believed that of energy -18 -18 0.41 x 10 0.41 x 10 energy released f photon Planck’s constant h Joules The Puzzle Pieces Bohr had to Solve Model would be released when an electron went from orbit 4 to orbit 2 in an atom. (1) Bohr knew he could use Max Planck’s equation to connect the energy of a light wave to its frequency (color). 1 = = 2 3 4

  31. Model Joules Niels Bohr believed that of energy -18 -34 -18 -18 0.41 x 10 0.41 x 10 6.63 x 10 0.41 x 10 Joules/second f f photon photon Joules Joules The Puzzle Pieces Bohr had to Solve Model would be released when an electron went from orbit 4 to orbit 2 in an atom. = h 1 = 2 3 4

  32. Model -18 -34 6.63 x 10 0.41 x 10 Joules · second -18 +34 cycles 0.41 x 10 x 10 f f second 6.63 photon photon Joules The Puzzle Pieces Bohr had to Solve Model = = 1 2 3 4

  33. Model +16 0.062 x 10 0.41 x 10 = -18 +34 cycles cycles cycles 0.41 x 10 x 10 6.63 f f f second second second 6.63 photon photon photon = The Puzzle Pieces Bohr had to Solve Model = +16 1 2 3 4

  34. Model cycles cycles f f second second photon photon = = The Puzzle Pieces Bohr had to Solve Model +16 0.062 x 10 +14 6.2 x 10 1 2 3 4

  35. Model -18 0.41 x 10 cycles second The Puzzle Pieces Bohr had to Solve Model Joules Niels Bohr now believed that the of energy released from an atom when an electron went from the atom’s fourth orbit to its second orbit was a photon of light that had a frequency of +14 6.2 x 10 Niels Bohr also knew the relationship between the frequency of a light wave and its wavelength. 1 2 3 Do you remember that equation? 4

  36. Model cycles second Shortest distance between the dotted lines is the wavelength of this wave. -18 0.41 x 10 speed of light frequency of light wave length of a wave The Puzzle Pieces Bohr had to Solve Model Joules Niels Bohr believed that of energy is the energy associated with a light wave that has a frequency of +14 6.2 x 10 l = 1 2 3 4

  37. Model cycles second Shortest distance between the dotted lines is the wavelength of this wave. -18 0.41 x 10 cycles second meters +8 3.0 x 10 second length of a wave +14 cycles 6.2 x 10 second The Puzzle Pieces Bohr had to Solve Model Joules Niels Bohr believed that of energy is the energy associated with a light wave that has a frequency of +14 6.2 x 10 speed of light l = +14 6.2 x 10 1 2 l = 3 4

  38. Model Shortest distance between the dotted lines is the wavelength of this wave. -14 -6 +8 meters +8 3.0 x 10 3.0 x 10 x 10 -6 meters meters meters 3.0 x 10 0.48 x 10 second length of a wave cycle cycle cycle +14 cycles 6.2 6.2 6.2 x 10 second The Puzzle Pieces Bohr had to Solve Model l = l = l = 1 2 l = 3 4

  39. Model Shortest distance between the dotted lines is the wavelength of this wave. meters meters length of a wave cycle cycle The Puzzle Pieces Bohr had to Solve Model -6 l = 0.48 x 10 l -9 = 480 x 10 1 2 l = 480 nanometers 3 4

  40. Model +14 cycles 6.2 x 10 second -18 0.41 x 10 Joules The Puzzle Pieces Bohr had to Solve Model After all this work, Bohr now believed that a photon released from an atom when an electron went from orbit 4 to orbit 2 in the same atom would have the following characteristics: l

  41. Model +14 cycles 6.2 x 10 second -18 0.41 x 10 Joules The Puzzle Pieces Bohr had to Solve Model Energy = Frequency = Wavelength = 480 nanometers Bohr also knew Balmer’s equation for determining the wavelength of the light waves that are emitted from hydrogen gas. l

  42. Observations Model Theory æ ö 1 1 1 1 ç ÷ = - ç ÷ l 2 2 91 nm n n è ø 1 2 (1) Wavelength when n = 3 and n = 2. (2) Wavelength when n = 4 and n = 2. 2 2 1 1 Bohr Puts the Pieces Back Together Bohr did this by using Balmer’s equation to see if that equation will give an answer of 480 nanometers. Lets try using the Balmer equation to find a light’s wavelength for two different situations.

  43. Observations Model Theory = l = -1 ] 1 1 1 [ -1 ( ) ] - [ ( 5 ) 1 2 2 2 3 91 91 36 -1 -1 [ ] [ ] ( ) 1 1 ( (9 -4) ) 1 1 - 91 2 n2 2 n3 91 (49) -1 (1) Wavelength when n = 3 and n = 2. [ ] ( ) 2 1 1 0.14 91 [ ] -1 0.0015 Bohr Puts the Pieces Back Together l = ? = = l = 670 nanometers = Bohr model expects a transition of an electron from orbit 4 (n=4) back to orbit 2 (n=2) to have a wavelength of 480 nanometers. Balmer’s equation says that a transition from n=3 to n=2 produces a light with a wavelength equal to 670 nanometers.

  44. Observations Model Theory = l = -1 ] 1 1 1 [ ( ) - 2 2 2 4 91 -1 -1 -1 [ ] ] [ ] (16 -4) -1 [ ( ) [ ( ] ) ( 12 ) 1 1 1 l ( ) 1 1 1 = ? = = 0.19 - 91 91 64 91 (416) 2 n2 2 n4 91 (2) Wavelength when n = 4 and n = 2. [ ] -1 2 1 l = 0.0021 = Bohr Puts the Pieces Back Together Do you think the answer is going to be greater or less than 670 nanometers this time? Why? 480 nanometers

  45. Observations Model Theory l l = = = = 480 nanometers 670 nanometers -1 -1 [ [ ] ] ( ( ) ) 1 1 1 1 1 1 - - 2 2 2 2 2 2 4 3 91 91 (2) Wavelength when n = 4 and n = 2. (1) Wavelength when n = 3 and n = 2. 2 2 1 1 Bohr Puts the Pieces Back Together Bolmer’s equation developed in 1885 says; Bohr atomic model (1913) expects a transition of an electron from orbit 4 back to orbit 2 to have a wavelength of480 nanometers. Bohr’s atomic model works for the hydrogen atom.

  46. Summary of Bohr’s (Planetary) Model (1913) Electrons orbit the nucleus in different orbits at different fixed distances. Electrons that leave one orbit must move to another orbit. Electrons only change orbits if specific amounts (quanta) of extra energy from the outside world are involved. Electrons that receive enough extra energy from the outside world can leave the atom they are in. Electrons that return to orbits they used to reside in give up the extra energy they acquired when they moved in the first place. Electronic energy given up when electrons move back into an original orbit often show up as a specific color light.

  47. Good news! Bohr’s model explains the light waves that are emitted by hydrogen! Bad News! Bohr’s model does not explains the light waves that are emitted by any other atom! Good news! The expanded quantum theory does explain light waves that are emitted by other atoms!

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