Lecture1'10: The Bohr Model

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Lecture-1.10 The Bohr Model Bright-Line
Spectra
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The Bohr Model Bright-Line Spectra

• How does Bohrs atomic theory explain the unique
  bright-line spectra of the elements?
• The farther an electron is from the nucleus, the
  more energy that electron will have.

1st shell 2nd shell 3rd shell
low energy
Nucleus

higher energy
Empty space
even higher energy
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The Bohr Model Bright-Line Spectra

• Recall that a H-1 atom has one proton and no
  neutrons.
• Recall that a H-1 atom has one electron in the
  1st shell when in the ground state.

1st shell 2nd shell 3rd shell
low energy
Nucleus
e-
1p 0n
higher energy
Empty space
even higher energy
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The Bohr Model Bright-Line Spectra

• If a H-1 atom were to absorb a precise amount of
  energy, its electron could jump up to a higher
  energy electron shell.
• The electron is now said to be in an excited
  state.

1st shell 2nd shell 3rd shell
e-
low energy
Nucleus
e-
1p 0n
higher energy
Empty space
even higher energy
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The Bohr Model Bright-Line Spectra

• Electrons are in the excited state when they in a
  shell that is higher than their ground state.
• Electrons can only jump up to an excited state by
  absorbing a precise amount of energy.
• All electrons in the excited state will return to
  their ground state.
• Electrons can NEVER jump to a shell that is lower
  than their ground state.

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The Bohr Model Bright-Line Spectra

• The excited electron can release all of its
  absorbed energy and jump back to its proper place
  in the atom the 1st shell.
• The electron has now returned to its ground state.

1st shell 2nd shell 3rd shell
e-
low energy
Nucleus
e-
1p 0n
higher energy
Empty space
even higher energy
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The Bohr Model Bright-Line Spectra

• An excited electron can release part of its
  absorbed energy and jump back toward its proper
  place in the atom.
• The electron is still in an excited state.

1st shell 2nd shell 3rd shell
e-
low energy
Nucleus
e-
1p 0n
higher energy
Empty space
even higher energy
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The Bohr Model Bright-Line Spectra

• Whether an excited electron releases some or all
  of its absorbed energy, the emitted energy is
  always released as photon a packet of light
  energy.

1st shell 2nd shell 3rd shell
e-
low energy
Nucleus
e-
1p 0n
higher energy
Empty space
even higher energy
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The Bohr Model Bright-Line Spectra

• The larger the jump back is, the higher energy
  the released photon will be.
• When an electron jumps back to the 1st shell in a
  hydrogen atom, the released photon will be in the
  ultraviolet region of the light spectrum.
• When an electron jumps back to the 2nd shell in a
  hydrogen atom, the released photon will be in the
  visible region of the light spectrum.
• When an electron jumps back to the 3rd shell in a
  hydrogen atom, the released photon will be in the
  infrared region of the light spectrum.

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The Bohr Model Bright-Line Spectra

• The four lines of the visible bright-line
  spectrum for a sample of hydrogen are produced by
  the following electron jumps.

An electron jumping from the 5th shell to the
2nd shell
An electron jumping from the 3rd shell to the
2nd shell
An electron jumping from the 6th shell to the
2nd shell
An electron jumping from the 4th shell to the
2nd shell
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The Bohr Model Bright-Line Spectra

• Bohrs atomic theory also includes an advanced
  mathematical equation that predicts the energy of
  each released photon with the energy jumps of the
  electrons!
• Unfortunately, Bohrs equation can only exactly
  predict the energy for the released photons of
  hydrogen!

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The Bohr Model Bright-Line Spectra

• Even though Bohrs atomic model has some serious
  flaws, it is still used to explain many chemical
  phenomena.
• Ex.1) Which electron shell has the most energy?
• (1) 1st shell (3) 3rd shell
• (2) 2nd shell (4) 4th shell
• Ex.2) An electron becomes excited by
• (1) absorbing energy (3) producing energy
• (2) releasing energy (4) destroying energy

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The Bohr Model Bright-Line Spectra

• Ex.3) What is the electron configuration for
  copper in the ground state?
• (1) 2-4 (3) 2-8-15-2
• (2) 2-8-13-1 (4) 2-8-18-1
• Ex.4) Which of the following could be an
  electron configuration for copper in the
  excited state?
• (1) 2-8-18-1 (3) 2-7-18-2
• (2) 2-9-17-1 (4) 2-8-18-2

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The Bohr Model Bright-Line Spectra

• Ex.5) In order for an excited state electron to
  return to the ground state it must
• (1) absorb energy (3) store energy
• (2) release energy (4) destroy energy
• Ex.6) A line in an elements bright-line spectrum
  is produced when
• (1) a ground state electron absorbs energy
• (2) an excited state electron releases energy
• (3) an excited state electron absorbs energy
• (4) a ground state electron releases energy

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The Bohr Model Bright-Line Spectra

• Ex.7) Which of the following types of light has
  the most energy?
• (1) radio waves (3) visible light
• (2) infrared light (4) ultraviolet light
• Ex.8) Which of the following colors in the
  visible spectrum has the most energy?
• (1) red (3) yellow
• (2) violet (4) blue

R
O
Y
G
B
V
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The Bohr Model Bright-Line Spectra

• Ex.9) A bundle of light energy is called a(n)
• (1) photon (3) wave
• (2) electron (4) quark
• Ex.10) In order for a ground state electron
  to jump up to a higher shell and become an
  excited state electron, it must
• (1) absorb an inexact amount energy
• (2) release an inexact amount energy
• (3) absorb a precise amount of energy
• (4) release a precise amount of energy

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The Bohr Model Bright-Line Spectra

• Ex.11) Who proved that white light was
  composed of all the colors of the rainbow?
• (1) Neils Bohr (3) Isaac Newton
• (2) Ernest Rutherford (4) John Dalton
• Ex.12) Which of the following gave evidence
  that electrons are found in energy shells
  around the nuclei of atoms?
• (1) the bright-line spectra of elements
• (2) elements combine in whole number ratios
• (3) cathode rays are attracted to a positive
  plate
• (4) 99 of alpha particles pass through gold
  foil