Bohr Model of the Atom

1
Bohr Model of the Atom

• Neils Bohr (1885-1962) developed a new model of
  H-atom by
• making the crucial assumption that not all of the
  classical
• physical laws apply to the atomic scale.
• Bohrs Postulates
• 1. Energy of H-atom is not a continuous function
  it can only exist in a limited number of
  discreet energy states---the energy is quantized!
• allowed states stationary states
• lowest ground state n 1
• others excited states n 2, 3, 4...

2
Bohr Model of the Atom

• Neils Bohr (1885-1962) developed a new model of
  H-atom by
• making the crucial assumption that not all of the
  classical
• physical laws apply to the atomic scale.
• Bohrs Postulates
• 1. Energy of H-atom is not a continuous function
  it can only exist in a limited number of
  discreet energy states---the energy is quantized!
• allowed states stationary states
• lowest ground state n 1
• others excited states n 2, 3, 4...
• 2. The atom does not radiate energy as long as it
  remains in a stationary state
• absorbs E goes from lower to higher state
• emits E goes from higher to lower state

3
Bohr Model of the Atom

• Neils Bohr (1885-1962) developed a new model of
  H-atom by
• making the crucial assumption that not all of the
  classical
• physical laws apply to the atomic scale.
• Bohrs Postulates
• 1. Energy of H-atom is not a continuous function
  it can only exist in a limited number of
  discreet energy states---the energy is quantized!
• allowed states stationary states
• lowest ground state n 1
• others excited states n 2, 3, 4...
• 2. The atom does not radiate energy as long as it
  remains in a stationary state
• absorbs E goes from lower to higher state
• emits E goes from higher to lower state
• 3. The different states correspond to different
  orbits of the electron.

4
Bohr Model of the Atom

• Neils Bohr (1885-1962) developed a new model of
  H-atom by
• making the crucial assumption that not all of the
  classical
• physical laws apply to the atomic scale.
• Bohrs Postulates
• 1. Energy of H-atom is not a continuous function
  it can only exist in a limited number of
  discreet energy states---the energy is quantized!
• allowed states stationary states
• lowest ground state n 1
• others excited states n 2, 3, 4...
• 2. The atom does not radiate energy as long as it
  remains in a stationary state
• absorbs E goes from lower to higher state
• emits E goes from higher to lower state
• 3. The different states correspond to different
  orbits of the electron.
• 4. Energy emitted or absorbed is quantized
  because the energy states are quantized ?E
  h?

from Plancks Einsteins work
5
Bohr Model of the Atom

• 1. Energy of H-atom is not a continuous function
  it can only exist in a limited number of
  discreet energy states---the energy is quantized!
• lowest ground state n 1
• others excited states n 2, 3, 4...
• 2. The atom does not radiate energy as long as it
  remains in a stationary state
• absorbs E goes from lower to higher state
• emits E goes from higher to lower state
• 4. Energy emitted or absorbed is quantized
  because the energy states are quantized ?E
  h?

6
Energy of a Bohr Orbit
orbit

• from classical physics
• E -e2 r n2h2
• 2r
  4?2me2
• so, En -2?2me4 -RHhc
• n2h2 n2
• ?

Plancks constant
charge
orbit radius
mass
From this, can derive Balmer equation!
7
Bohr Model Energy States for Hydrogen
Bohr (Quantized) model can explain line spectra
for hydrogen.
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