• Anyone who is not shocked by quantum
mechanics has not understood it.
—Neils Bohr (1885–1962)
December 3
• Objectives:
• View emission spectrum of Hydrogen, identify
the color bands
• Understand Bohr’s model of the atom
Observations
• Look at the light produced by the hydrogen
lamp
• What color is it?
• Put on your diffraction glasses
• What colors can you see now?
Hydrogen Emission Spectrum:
• Pink light emitted from hydrogen
• When separated by a prism, shows
distinct bands of color
This means hydrogen
is producing specific
bands of light with
definite wavelengths/
frequencies.
Niels Bohr
Nobel Prize – 1922
• “For his services in the
investigation of the structure of
atoms and the radiation emanating
from them”
• Five facts from the next four slides…
Niels Bohr’s Atom (Slide 1 of 3)
• Electrons move around the nucleus in orbits, like a solar
system. The orbits are sometimes called energy levels.
Planetary Model
Electrons cannot exist
between orbits (energy
is quantized)
(Slide 1b of 3)
Electrons cannot exist between orbits – think
of rungs on a ladder. You can’t be in between
one rung and another.
Bohr’s Atom (Slide 2 of 3)
• Electrons closest to the nucleus are
lowest in energy.
• Electrons farthest from the nucleus
are highest in energy.
• Ground state- electrons are in the
lowest energy level possible
• Excited state - If energy is put into
the atom, the electrons will jump
up in energy (move away from the
nucleus)
Bohr’s Atom (Slide 3 of 3)
• Excited electrons
naturally go back to
ground state. In order to
do this, energy must leave
the atom. Because
energy is quantized in an
atom, the amount of
energy that leaves is the
difference in energy
between orbits.
• If this energy is in the
visible light range, we will
see certain colors
Atomic Spectra
• Absorption: When energy is added and an electron
moves from a lower energy level to a higher energy
level
• Emission: When an electron falls from a higher energy
level to a lower energy level and a photon is emitted.
The energy of each absorbed or emitted photon
corresponds to a particular frequency, E = hν
Hydrogen Atom Line Emission Spectrum
Ground State: Lowest energy
Excited State: Higher energy
When an electron “falls” from
higher to lower energy, it
gives off extra energy (E) as
a photon (E=hν)
Electron transitions
involve jumps of
definite amounts of
energy.
This produces bands
of light with definite
wavelengths.
Hydrogen Emission Spectrum:
• Pink light emitted from hydrogen
• When separated by a prism, shows
distinct bands of color
Electron at
highest energy
level produces
what kind of
EMR? - UV
The electron at
lowest energy
level? - Red
IMPLICATIONS
Classical Theory: (old)
• Any amount of energy could be absorbed or
emitted
Quantum Theory: (new)
• Hydrogen atoms can only have EXACT energy
levels
One More Thing in the Notes
• Summary: Write a 1-2 sentence summary of
the Bohr model of the atom and the hydrogen
emission spectrum.
Flame Tests
Many elements give off characteristic light which can
be used to help identify them.
strontium
sodium
lithium
potassium
copper
Next time - Thursday
• Flame Test Lab
• You will determine the emission spectra of a
number of elements using colored flames
• Close-toed shoes
• Ladies: Something to tie your hair back