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Bohr’s Model of the Atom
Chapter 5
• The Modern • The atom is mostly
View of the
empty space.
Atom
• Two regions
1. The Nucleus – Protons
and neutrons are
located in the nucleus.
2. Electron cloud region –
Place where you might
find an electron.
• The Atom is • From his measurements,
Rutherford estimated the
mostly
radius of an atom to be
empty space
100,000 times greater
than the radius of the
nucleus. This is
comparable to the
thickness of a dime to
the length of football
field
Max Planck’s
Quantum Theory
• What did
• Atom energy is
Planck
absorbed or
proposed?
liberated in packets
or chunks of energy.
• Quanta =
Planck called these
plural
packages
of
energy
• Quantum =
"quanta".
singular
• Photon
• The Quantum of Light = the
Photon.
• Particles of light are called
light quanta or photons.
Energy of a Photon = h x u
E
= h x u or E = h x f
h is Planck’s constant
h=
6.63 x 10-34 J.s
u is equal to the frequency of light.
u = f = frequency
Packet of energy in a photon is so small
that we are not aware of the rain of
photons of light impinging on our eyes –
just as you cannot feel the impact of
individual air molecules.
The quantum concept
• Max Planck
(1900)
– Introduced
quantized
energy
• Einstein
(1905)
– Light made
up of
quantized
photons
• Higher frequency photons = more
energetic photons
Bohr’s atomic model
• Niels Bohr
puts it all
together
• Bohr added Planck’s
quanta idea (which was
proven by Einstein and
Louis de Broglie’s
wave/particle theory) to
the Rutherford’s atomic
model.
• Electrons exist at set levels
of energy, at fixed distances
from the nucleus.
• When an atom absorbs
energy, the electron jumps
to a level further from the
nucleus
• If it radiated energy, that
means that the electron is
falling to a level closer to the
nucleus.
• The protons and neutrons
are located in the nucleus.
• The electrons are located
at different energy shells
(energy levels around the
nucleus)
Energy Levels/shells
• There are several
energy levels in which
an electron might be
found.
ee-
• To move from one
level to another an
electron must gain or
lose an exact amount
of energy. Quantum
ee-
2
electron
Bohr’s T heory
Three rules:
• Electrons only exist in certain
allowed orbits
• Within an orbit, the electron
does not radiate
• Radiation is emitted or
absorbed when changing
orbits