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Transcript
Sections 6.3-6.5
The Bohr Model, Wave Model,
and Quantum Model
Objectives
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•
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Draw Bohr Models
Describe the wave behavior of matter
Arrange electrons in an atom
Identify energy levels
Apply Heisenberg’s Uncertainty Principle
Describe the quantum mechanical model
Key Terms
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•
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Ground state
Excited states
Matter waves
momentum
Uncertainty
principle
•
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Wave functions
Probability density
Electron density
Orbitals
Electron shell
subshell
Bohr Model of the Atom
• In 1913 Niels Bohr proposed
quantum model for the H atom
• Bohr proposed H atom has only
certain allowable energy states
• Lowest state= ground state
• Gaining energy = excited state
Bohr Model of the Atom
• Electrons move in certain, specific,
circular orbitals
• Smaller orbit = lower energy level
• Assigned the allowable electron orbitals
the principle quantum number, n.
• 1st orbit= lowest energy: n=1
• 2nd orbit= 2nd lowest energy: n=2
Bohr Model of the Atom
• Energy is added to an atomelectron
moves to higher energy level
• Electron in “excited state” drops to a
lower energy orbit emits a photon
E = E
higher-energy orbit
– E
lower-energy orbit=
E
photon=
h
Bohr Model of the Atom
• Problems with Bohr’s model
– Only explained H
– Did not explain why electrons
should only be allowed certain,
specific energy levels
De Broglie
• 1924
• Electrons, like light also had a
particle-wave dual nature
• Only multiples of half wavelengths are
allowed in circular orbits
1 half-wavelength
2 half-wavelengths
3 half-wavelengths
De Broglie
• Formulated an equation for the
wavelength, mass, and velocity of a
particle
h

mv
Heisenberg Uncertainty
Principle
– Fundamentally impossible to know
precisely both the velocity AND
position of a particle at the same
time.
– Cannot measure an object
without disturbing it
Quantum Mechanical Model
• 1926
• Schrödinger
• Limited electrons to only certain energy levels
– Atomic orbital: 3 dimensional area around the
nucleus that predicts the 90 % PROBABLE
location of an electron
Electron Density
Diagram
Quantum Mechanical
Model
• Assigns principal quantum numbers
(n) relative to sizes and energies of
orbitals
• (n) specifies atom’s major energy
levels= principle energy levels
• Lowest level= ground state= n= 1
• H has 7 energy levels, n= 1 to
7
Quantum Mechanical Model
• Principal energy levels contain energy
sublevels
• Principal energy level 1 has 1
sublevel
• Principal energy level 2 has 2
sublevels
• Principal energy level 3 has 3
sublevels
Energy Sublevels
• s, p, d, and f
• Labeled according to shapes of
orbitals
• s = spherical
• p = dumbbell
• d and f = not all have same
shape
s and p orbitals
Three p orbitals
d orbitals
Energy Sublevels
• Each orbital contains 2 electron at most
• Principal energy level 1 has 1 sublevel: 1s orbital
• Principal energy level 2 has 2 sublevels: 2s and 2p
• 2p sublevel has 3 dumbbell-shaped p orbitals (2px,
2py, and 2pz)
• Principal energy level 3 has 3 sublevels: 3s, 3p, and 3d
• d sublevels have 5 orbitals
• Principal energy level 4 has 4 sublevels: 4s, 4p, 4d,
and 4f
• f sublevels have 7 orbitals