Modern Atomic Theory Notes
Electromagnetic radiation – energy that travels through space as waves.
Waves have three primary characteristics:
1. Wavelength (- lambda) – distance between two consecutive peaks or troughs in
a wave. Unit = meter
2. Frequency (  = nu) – indicates how many waves pass a given point per second.
Unit = Hertz (Hz)
3. Speed – velocity - indicates how fast a given peak moves in a unit of time
c = speed of light = 3 x 108 m/sec
c = 
Electromagnetic radiation (light) is divided into various classes according to wavelength.
Wave- Particle Theory – Light as waves – Light as photons
Photon/quantum – packet of energy – 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
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?
Excited State – atom with excess energy
Ground State – lowest possible energy state
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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 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
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
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, then d, then f
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
- ** A max of two electrons can occupy an orbital**
- an orbital can be empty, half-filled, filled
Electron Configuration – arrangement of the electrons among the various orbitals of the
atom
Examples)
Neon:
Sulfur:
Cd:
Na:
Summary
Principle
Energy Level
# of sublevels
# of orbitals
present
s p d
f
Total # of
orbitals
Maximum #
of electrons
Shapes of orbitals
- All s orbitals are spherical as the principle energy level increases the diameter
increases.
-
All p orbitals are dumbbell shaped – all have the same size and shape within an
energy level
-
All d orbitals are flower (clover) shaped and a donut – all have the same size and
shape within an energy level
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
Examples)
____ half-full
____ empty
Aufbau Order – Tool to predict the order in which sublevels will fill
Noble Gas Configuration – Shorthand configuration that substitutes a noble gas for
electrons
Examples)
Na:
Sn:
Valence Electrons – Electrons in the outermost (highest) principle energy level in an atom
Core Electrons – innermost electrons – not involved in bonding
Valence Configuration – shows just the valence electrons
Examples)
Na:
Sn:
__________________________________________________________________________
Give the electron configuration for the following.
Beryllium:
Bromine:
Yttrium:
Give the noble gas notation for the following.
Fluorine:
Lead:
Silver:
Draw the orbital diagram for the following.
Magnesium:
Vanadium: