Download Chapter 5 PPT/Notes B

The Quantum Mechanical
Model
•By the mid-1920’s scientists were convinced that
the Bohr model needed modification…
•Louis de Broglie(1892-1987) proposed an idea to
fix the energy levels for the Bohr model.
•De Broglie proposed that all particles traveled as
waves and proposed the wave formula for the
electron orbits. (see p149)
•Problem:
What is the wavelength of an electron moving at
5.31 x 10 6 m/sec?
Louis de Broglie
De Broglie’s Electron Wave
• Solution:
de Broglie's equation is
λ = h/mv
λ = 6.626 x 10 -34 J·s/ 9.11 x 10 -31 kg x 5.31 x 10 6 m/sec
λ = 6.626 x 10 -34 J·s/4.84 x 10 -24 kg·m/sec
λ = 1.37 x 10 -10 m
λ = 1.37 Å
Answer:
The wavelength of an electron moving 5.31 x 10 6 m/sec is 1.37 x
10 -10 m or 1.37 Å.
De Broglie’s Electron Waves
• The below pattern is of electrons passing
through a single crystal . Bright spots are
antinodal, dark spaces are nodal
Electrons As Waves
• A consequence of this theory are considerable
paradoxes. Young's Double Slit experiment can and has
been carried out with electrons, protons, neutrons and
various molecules including C60 - "buckminsterfullerene"
- that extraordinary form of carbon shaped as a soccer
ball.
• If single objects approach a double slit, they pass
through and slowly build up, one by one, the double slit
pattern. Shut one slit off and they, one by one, create the
single slit diffraction pattern.
Question: How do single "objects" "know" of the
existence of two slits? "Clearly" they only pass through
one slit! ( But if they only pass through one slit, why the
two slit pattern.................HELP!!!)
• http://www.launc.tased.edu.au/online/sciences/physics/d
ebroglie.html
• Young’s Slit Experiment
Electrons as waves
• Electrons can only
make orbits with
whole numbers of
waves…..
Electrons as Waves
The Heisenberg Uncertainty
Principle
• H.U.P states that you cannot know, with
certainty, both the velocity and location of
a moving particle.
The Schrodinger Wave Equation
• In 1926, Erwin Schrodinger developed the
quantum mechanical model of the atom.
• His model developed a ‘probable’ location
for electrons mathematically.
• Each electron can be described by
quantum numbers…sub-levels and
orbitals.
Quantum Numbers
1. Principal quantum number = n… each major
energy level is called a principal energy level…
n also tells how many sub-levels are present…
1 for n=1, 2 for n=2, etc
2. Principal energy levels contain energy sublevels… s,p,d,f
3. Orbitals…s has 1 orbital, p has 3 orbitals, d
has 5 orbitals, and f has 7 orbitals
https://www.youtube.com/watch?v=accyCUzasa0
5.3 Electron Configurations
• Use the Aufbau diagrams to build electron
configurations.
• Numbers represent principal energy levels
• Letters s,p,d,f represent sub-levels
• The superscript tells you electrons present
in an orbital
Ground-State
• Ground-state configuration would be an atom
at its lowest energy level.
• We use 3 rules to write configurations…
• The Aufbau principle says electrons fill the
lowest energy levels first.
• Hund’s rule says to place one electron in each
orbital before placing the 2nd one of opposite
spin.
• The Pauli Exclusion Principle states that an
atomic orbital can hold, at most, 2 electrons.
• We use arrows to
designate electrons…
up for +1/2 and down
for -1/2 spin.
• Use your Aufbau
diagram and fill using
the 3 rules… for
fluorine and neon….
Orbital Shapes(See p 158 )
For Neon Orbital Diagram
Noble-Gas Configuration Notation
• A short-cut for writing
configurations would
use brackets and the
noble-gas symbol to
designate start here
and write the rest of
the configuration
Electron Configurations…
Examples
The Periodic Table and s,p,d,f
Credits
• UC Davis Science
• http://chemwiki.ucdavis.edu/Physical_Chem
istry/Quantum_Mechanics/Quantum_Theor
y/De_Broglie_Wavelength
• Bozeman Science
https://www.youtube.com/watch?v=accyCU
zasa0
• Matter and Change, McGraw Hill, chapter 5,
p134-163.