History of Quantum Theory
At the turn of the 20th century, classical physics was well defined and physicists thought they
could explain all naturally occurring phenomena.
• X-rays were discovered (Roentgen).
• Radioactivity of Uranium salts (Bequerel).
• Plank proposes E=hv (light as quantized energy packets)
• Einstein provides another example of the quantization of energy when he explains
the photoelectric effect.
• Rutherford’s gold foil experiment, J.J. Thompson’s plum pudding goes bad.
• Bohr puts it all together to explain the absorption spectrum of hydrogen.
Photoelectric effect
In 1905, Einstein further solidified the idea of quantized energy packets. Basically, he
showed that it took a certain amount or threshold of energy (certain frequency) to kick an
electron out of a metal. In the photoelectric effect, it takes a single photon to emit a single
electron. Any excess energy goes into the kinetic energy of the emitted electron. Additional
photons eject additional electrons.
3 Rules for Electron Configurations:
1. Aufbau principle
2. Pauli exclusion principle
3. Hund’s rule
Angular momentum (orbital) quantum number, l, give the sublevel (s, p, d, f) l = 0, 1, 2, 3
1/2 life
Xo = original amount
X = amount remaining after time t
ln .6 Xo = - k t
Xo
k = .693 = 1.21 x 10-4
5720
ln .6 = - 1.21 x 10-4 t
t = 4220 years
Ion Size
As with atoms, the size of ions increases as you go down the periodic table and decreases as you go
across, if you consider cations and anions separately. However , when you switch from cations to anions
in a horizontal row, the size increases.
Ionization energy: This is the energy required to remove the outermost electron. The bigger the
difference between the shielded nucleus and the outer electrons the bigger I.E. Watch out for
jumps that occur because of orbital stability issues. Like when you lose a lone p-electron and
then try to remove the next electron from an s-sublevel. That will require a big jump in energy
because the s-sublevel is of lower energy and more stable. The higher energy p-electron takes
less energy to remove.
Also, each successive electron requires more I.E. Remember cations are smaller than
atoms, so outer electrons are held more tightly by nucleus.
Lewis Structures
1. Count total number of valence electrons (add electron for negative ions, subtract for positive ions.)
2. Divide by two to get number of electron pairs.
3. Determine central atom (usually lowest electronegativity; never hydrogen)
4. Place one pair between each pair of bonding atoms (sigma bonds)
5. Assign electron pairs to terminal atoms to complete octets.
6. Assign any extra electrons to central atom.
7. If central atom does not have octet, you may complete the octet by forming double bonds if
atoms are O, C., S, N, or P.
Intermolecular Forces
Vapor Liquid Equilibrium
 Equilibrium is dynamic. Things don’t stop happening, they just stop changing.
 Vapor Pressure: The pressure exerted by the vapor above a liquid when the liquid and vapor are in
equilibrium.
 Vapor pressure depends upon temperature. The higher T, the easier time molecules have leaving the
liquid phase.
 Vapor pressure is independent of the volume of the system.
 Boiling point: eq vapor pressure = pressure of atmosphere. The vapor pushes back the atmosphere.
Critical Phenomena
 Critical temperature: the temperature above which vapor cannot be liquefied not matter what
pressure is applied.
 Critical pressure: Pressure required to produce liquefaction at critical temperature.
Phase Diagrams
 Be able to tell what is happening on the lines
 Identify the triple point. Triple point of water is 0.01C.
 Identify phase changes: evaporation, fusion, sublimation
Raoult’s Law
Raoult’s Law allows you to calculate the partial pressure that a species will exert when it is a
component of a solution. We know that a pure liquid exerts a vapor pressure. This equation allows you
to find the pressure exerted by all members in a solution..
PA = XAPo
This just says that the partial pressure of species A (PA) is equal to the mole fraction of species A in the
solution (XA ) times the vapor pressure of pure A (Po ) at the specified temperature.
Henry’s Law
Henry’s Law is less emphasized than Raoult’s Law but you should still know what it is. Henry’s
Law says that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas
over the solution.
Cg = k Pg
You often have to solve for k, the Henry’s Law constant at one set of conditions and then calculate the
solubility (Cg) at another pressure (Pg ).
(large # of e-)
Dipole
Determining rate laws from concentration vs initial rate data.
These problems assume initial rates where concentrations are constant.
Determining rate laws from concentration vs time data. For these problems, the concentration is
constantly changing. These problems are a little harder than concentration vs rate problems because you
have to look at the behavior of the entire data set to determine the rate relationship. The whole name of
the game here is what form of the concentration of reactant A, [A}, do you need to plot against time, t, in
order to get a linear relationship.
Solutions and Colligative Properties
Mass % Solute
ppm
mass solute
X 100%
total mass solution
mass solute =
total mass soln
ppb
X
106 g
mass solute =
total mass soln
X
109
Remember that when you add something to a solution you change the total mass of the solution. You
have to keep track of what you add, not just the amount of solvent that you start with.
Molarity, M
M =
moles solute
liters of solution



Molarity is almost always used for concentration in chemistry problems.
[ A ] square brackets mean the concentration of A in molarity.
Be able to relate moles and volume MV = n
(molarity x volume = moles)
Molarity Dilution
Mc Vc = Md Vd
Molality, m
m=
moles solute
kilograms solvent
Freezing and Boiling Point Change
Tf = kfmi
Tb = kbmi

Here it doesn’t matter how much solute you add, it’s always based upon the number of kilograms of
solvent present.

Use molality in colligative properties problems, i.e. boiling point elevation, freezing point depression