Electrons as
Particles and
Waves
Electrons Behave Like Particles
and Like Waves
It is not necessary, or useful, to say that an electron is a
particle - or a wave - just that in certain circumstances it behaves like a
wave, and in others like a particle
wave-particle duality holds that light and matter (we’re
discussing electrons) can exhibit properties of both waves and of
particles
If an electron behaved ONLY like a particle, it would be much
easier to discuss its location and its path…
Think of baseball…..
Electron as a Particle
Because the ball behaves like a
particle, we can say that the ball
will follow a well-defined path
from the pitcher to the catcher
Electron as a Wave
If the baseball had BOTH wave
and particle behaviors, the path
of the baseball could not be
precisely determined. The best
we could do would be to make a
probability map of where the
baseball will cross home plate
Light Waves
Light Phenomenon
Long wavelength ----> small
frequency
Short wavelength ----> high
frequency
Electromagnetic Spectrum
Note the small area for visible light!
e- normally occupy the lowest energy
level that will hold it = Ground State
After the e- gains energy = Excited
State “Absorption”
To drop down to Ground state an eloses energy as light “Emission”
Similar to the electromagnetic
spectrum, each element has its own
specific Atomic Emission Spectrum
(lines of color) like a fingerprint
Atoms and Light
The movement of electrons inside of atoms produces light and
other electromagnetic radiation thanks to quantum mechanics.
Each element gives off only certain frequencies of light, called
spectral lines.
In effect each element has its own signature of spectral lines
allowing us to identify which element we have or what stars are
made of.
Helium
Plancks Constant
A physical constant utilized to
describe the relationship between
energy and frequency
v = E/h
h = 6.626 x 10-34 plancks constant
C = λv
E = Energy in Joules (m2 x kg)
E = hc/λ
f or v = frequency
c = 3.00 x 108 m/s the speed of
light
E = hv
Photons
Max Planck in 1900 stated that the light emitted by a
hot object (black body radiation) is given off. in discrete
units or quanta. The higher the frequency of the light
the greater the energy per quantum.
Electrons as Particles
Quanta: Light is energy that occurs
in discrete packets
Photon: Each packet of light energy
is called a photon
Photons behave like particles
because they have the ability to
move other matter (momentum).
Photoelectric Effect: e- are ejected
(released) from metals when light
with high energy shines on them
The photoelectric effect
demonstrated the particle behavior
of light!!
Quantum Mechanic Model
In the quantum-mechanical model, specific electron orbits are not
appropriate: the electron's movement cannot be known that precisely.
Instead, we map the probability of finding the electron at various
locations outside the nucleus. The probability map is called an
orbital/electron cloud.
Three Rules for Writing
Notations
Aufbau principle - electrons enter orbitals of the lowest energy first
the 7 main energy levels can have overlapping sublevels
EX: that a 5 level is really higher than a 6 level
Pauli exclusion principle - no two electrons can have the same 4
quantum numbers this limits the number of electrons in each orbital to
2: 1 spin up ↑, and 1 spin down ↓
Hund’s Rule - when electrons occupy orbitals of equal energy, ONE
electron enters each orbital until ALL are ½ filled with electrons spinning
in the same direction (all up or all down), then the orbitals are filled
with the spin electrons
Electron Configuration
Shorthand
Shorthand Notation (Noble Gas
Core notation):
Instead of writing the whole
electron configuration notation,
the symbol for the last element
(noble gas) in the previous row of
the periodic table, in brackets, is
used for all the electrons up until
that principle level or row [ ] n s
Lewis Dot Structures
Lewis Dots show only the
electrons available for bonding,
called the valence electrons. These
are the electrons in the last
principal quantum (energy) level.
They are filled in around the
element symbol starting at the
top, and going around clockwise 1
on each side and continuing to 2
on each side