The Quantum Model of the Atom
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Only works for Hydrogen
Why couldn’t electrons jump to any level –
not just specific energy levels?
Why didn’t atom collapse?
What about the chemical behavior of atoms?
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Postulated electrons
also have a dual
wave-particle nature
Electrons act like
waves confined
around the nucleus
(standing waves) and
therefore could only
have certain
frequencies
Video – Tacoma
Narrows Bridge
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These correspond to
the energy of Bohr’s
orbits.
Investigation showed
that electrons can be
diffracted and can
interfere with each
other
These are wave
properties
Electrons have a dual
wave-particle nature.
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Locate electrons
using photons
Photons change
position and/or
velocity of an
electron
Demo
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is impossible to know both
the position and the velocity of
an electron or any other
particle.
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Developed very complicated equations
Equations treated electrons as waves
Solution of the equation allowed for only
specific energies and frequencies of waves
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Their ideas led to a new theory of the atom
Call Quantum Theory/Quantum Mechanics
Describes mathematically the wave properties
of electrons and other small particles
Waves in macroscopic vs. microscopic
particles
Give us only an area of probability of finding
an electron
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Use the concept of orbital (area where it is
likely you will find the electron) rather than
orbit (path of the electron)
Orbital – three dimensional region around the
nucleus that indicates the probable location
of the electron
Orbitals described by 4 Quantum Numbers
which indicated the properties of the orbitals
and the electrons in those orbitals.
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First three result from the solution of
Schrödinger’s Wave Equations
Fourth is the spin of the electron
Quantum numbers are n, l, m, s
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Called the Principal Quantum Number
Gives energy level and period
As n increases electron energy increases
As n increases the distance from the nucleus
to the electron increases
Always a positive integer (n = 1, 2, 3, 4, …)
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Number of orbitals in an energy level = n2
◦ 1st Energy Level – 1 orbital
◦ 2nd Energy Level – 4 orbitals
◦ 3rd Energy Level – 9 orbitals
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Number of electrons in an energy level = 2n2
◦ 1st Energy Level – 2 electrons
◦ 2nd Energy Level – 8 electrons
◦ 3rd Energy Level – 18 electrons
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Called the angular momentum Quantum
Number
Gives the shape of the orbital
l = 0, 1, 2, …., (n-1)
Shapes associated with letters
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Stand for names given to groups of lines in
the spectra of alkali metals
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s – sharp
p – principal
d – diffuse
f – fundamental
After f – orbitals are alphabetical, i.e. g, h, i,
etc.
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1st Energy Level – 1 Orbital – s
2nd Energy Level – 2 Orbitals – s and p
3rd Energy Level – 3 Orbitals – s, p and d
Etc.
Shorthand
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1s
2s, 2p
3s, 3p, 3d
4s, 4p, 4d, 4f
Etc.
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Magnetic Quantum Number
Gives the Orientation of the Orbital in 3
dimensions
s – spherical – only 1 orientation
p – dumb bell – 3 orientations: px, py, pz
d – double dumb bell – 5 orientations
f – “CRAZY!!!” – 7 orientations
m = -l, …..0…….+l
So for p orbitals m = -1, 0, 1
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Accounts for magnetic properties of the
electron
Magnetic properties are due to the spin of the
charged electrons
Magnet demo
Each orbital can hold 2 electrons ( Remember
# of electrons = 2n2)
Values for s = + ½ and – ½
Demo – butterfly orbital
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The atom is like an
onion – in layers
Between each layer
is an area where
there are no
electrons – nodes