Modern Atomic Theory Notes
Electromagnetic radiation – energy that
travels through space as waves.
Waves have three primary
characteristics:
•
Wavelength (- lambda) –
distance between two
consecutive peaks or troughs
in a wave. Unit = meter
•
Frequency (  = nu) –
indicates how many waves
pass a given point per
second. Unit = Hertz (Hz)
•
Speed – velocity (c = speed
of light = 3 x 108 m/sec) indicates how fast a given
peak moves in a unit of time
c = 
Tell me what you know…
Which wave has the
greatest
wavelength?
Which wave has the
greatest
frequency?
Which wave has the
greatest speed?
Electromagnetic radiation (light) is divided
into various classes according to
wavelength.
Tell me what you know…
• Which color has the greatest wavelength?
• Which color has the shortest wavelength?
Wave- Particle
Theory – Light
as waves &
Light as
photons
Photon/quantum
– packet of
energy OR a
“particle” of
electromagnetic
radiation
Energy - (E – change in
energy) – Unit Joules (J)
Planck’s Constant –
(h = 6.626 x 10-34 J * s)
Ephoton = h
Change in Energy of a photon =
(Planck’s Constant) x (frequency)
c =  & Ephoton = h →
Ephoton = hc

Ex: What is the wavelength of light with a frequency of 6.5 x 1014 Hz? What
is the change in Energy of the photon?
E = hc ΔE = 4.3 x 10-19 J
= c = 3 x 108 m/sec
Given


= (6.626 x 10-34 J x s)(3 x 108 m/s)
6.5 x 1014 Hz
 = 6.5 x 1014 Hz
-7 m
4.6
x
10
-7
λ = 4.6 x 10 m
 = ? ΔE = ?
Tell me what you know…
• What does ΔE tell us about a photon?
Excited State – atom with
excess energy
Ground State – lowest
possible energy state
Wavelengths of light carry
different amounts of
energy per photon
Only certain types of
photons are produced
(see only certain colors)
Quantized – only certain
energy levels (and
therefore colors) are
allowed
Emission and Absorption Spectra
• Emission Spectrum – bright lines on a dark background. Produced
as excited electrons return to a ground state – as in flame tests.
Nucleus
Absorption Spectrum – dark lines in a continuous spectrum.
Produced as electrons absorb energy to move into an excited state,
only certain allowable transitions can be made. Energy absorbed
corresponds to the increase in potential energy needed to move the
electron into allowed higher energy levels. The frequencies
absorbed by each substance are unique.
Nucleus
Tell me what you know…
• How can we tell elements apart using
emission spectra?
Bohr Model – suggested that electrons move around the
nucleus in circular orbits
Only Correct for Hydrogen
Wave Mechanical Model – Described by orbitals gives no
information about when the electron occupies a certain
point in space or how it moves *aka – Heisenberg's
Uncertainty Principle
Parts of the Wave Mechanical Model
1. Principle Energy Level (n) – energy level
designated by numbers 1-7.
-called principle quantum numbers
1
2
3
4
5
6
7
2. Sublevel – exist within each principle energy level
-the energy within an energy level is slightly different
-each electron in a given sublevel has the same
energy
-lowest sublevel = s, then p,
s
p
d
then d, then f
f
Tell me what you know…
• Write the sublevels in order of highest
energy to lowest energy.
Parts of the Wave Mechanical Model
cont.
3. Orbital – region within a sublevel or energy
level where electrons can be found
s sublevel – 1 orbital
p sublevel – 3 orbitals
d sublevel – 5 orbitals
f sublevel – 7 orbitals
- ** No more than two electrons can occupy an
orbital**
-an orbital can be empty, half-filled, filled
Tell me what you know…
• How many total electrons are in each
sublevel (s, p, d, & f)?
Electron Configuration – arrangement of the electrons
among the various orbitals of the atom
Ex: 1s22s22p6 = Neon
Sulfur = 1s2 2s2 2p63s2 3p4
Cd = 1s2 2s2 2p63s2 3p64s2 3d10 4p65s2 4d10
Na = 1s2 2s2 2p63s1
Ne
Na
Summary
Principle
Energy
Level
# of
sublevels
# of orbitals
present
s p d
f
Total # of
orbitals
Maximum #
of electrons
1
1
1 - - -
1
2
2
2
13 - -
4
8
3
3
13 5 -
9
18
4
4
13 5 7
16
32
Shapes of orbitals
All s orbitals are spherical
as the principle energy level
increases the diameter increases.
All p orbitals are dumbbell or figure-8 shaped – all have the
same size and shape within an energy level
4 of the d orbitals are 4-leaf clover shaped and the
last is a figure-8 with a donut – all have the same
size and shape within an energy level
f orbitals are complicated!!!!!
Electron Spin
Spin – motion that resembles earth rotating
on its axis– clockwise or counterclockwise
Pauli Exclusion Principle – two electrons in the same orbital must have
opposite spins
Hund’s Rule – All orbitals within a sublevel must contain at least one
electron before any orbital can have two
Orbital Diagram – describes the placement of electrons in orbitals
• use arrows to represent electrons with spin
• line represents orbital (s=1, p=3, d=5, f=7)
____ full
____ half-full
____ empty
Orbital Diagrams
Ex: Neon = 1s__2s__ 2p__ __ __
Carbon = 1s__2s__ 2p__ __ __
Zinc = 1s__2s__ 2p__ __ __3s__ 3p__ __ __
4s__ 3d__ __ __ __ __
Gallium =1s__2s__ 2p__ __ __3s__ 3p__ __ __
4s__ 3d__ __ __ __ __ 4p__ __ __
Tell me what you know…
• Summarize each in four words or less:
– Spin
– Pauli Exclusion Principle
– Hund’s Rule
Aufbau Order
Aufbau Order – Tool to
predict the order in
which sublevels will
fill
OR use order on
Periodic Table
• Noble Gas Configuration – Shorthand
configuration that substitutes a noble gas for
electrons
Na = 1s22s22p63s1 or
[Ne]3s1
Ex:
Sn = 1s22s22p63s23p64s23d104p65s24d105p2
or
[Kr]5s24d105p2
• Valence Electrons – Electrons in the outermost
(highest) principle energy level in an atom,
electrons use in bonding
• Core Electrons – innermost electrons – not
involved in bonding
• Valence Configuration – shows just the valence
electrons
3rd Shell/1valence electron
Ex: Na = 3s1
Sn = 5s25p2
5th Shell/4 valence electrons