# [CHE 104] - Midterm Exam Guide - Ultimate 38 pages long Study Guide!

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7 Feb 2017
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West Chester University
CHE 104
MIDTERM EXAM
STUDY GUIDE
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January 23rd, 2017
Lecture #1
Review from chem 103
Ideal gas laws
No molecular volume
No intermolecular forces
Intermolecular forces
Forces between particles
If there were no intermolecular forces everything would be in gas state
intermolecular forces enable us to have liquid and solid states
Result from electrostatics
Like charges repel
+/+ and -/-
Unlike charges attract
“Opposites attract”
+/-
Ion to Ion interactions
Fully + particle with a fully - particle
+ particles are cations
- particles are anions
Coulomb’s Law
Force of attraction= k x ((n+ e)(n- e))/(d2)
k: proportionality constant
n+: charge on + ions (cations)
n-: charge on - ions (anions)
e: charge on electron
d: distance between ions (squared)
Don’t need to mathematically solve this equation for class but understand
general concepts
General concepts:
What would happen when you increase the charge of an electron?
(charge is in the numerator)
Force of attraction increases
Example: which is bigger? ½ or 3/2
3/2 is larger
Notice that by increasing the
numerator and having the same
denominator that the force of
attraction INCREASES
What would happen if you increase the distance between the
ions? (denominator)
Force of attraction decreases
Example: which is bigger? ½ or ⅓
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½ is larger
If you increase the distance the force
of attraction DECREASES
Ion to Dipole Interactions
An ion with a polar molecule
Reminder: polar has regions of partial + and partial - charges (S+ and S-)
Reminder: opposite charges attract, same charges repel
How to determine polar vs nonpolar
Example: water (H2O)
Steps
Look at molecular geometry by drawing lewis structure
Count lines and lone pair(s) to find shape
Is the molecule symmetrical?
If yes, nonpolar
If no, polar
Example below:
2 H: 2x1=2
1 O: 1x6=6
Valence electrons=8
Oxygen will have 4 groups (2 lines and 2 lone pairs)
Shape: tetrahedral
Rule of thumb
When there’s only Carbon and Nitrogen then most likely it
is nonpolar
Dipole to dipole forces
2 polar molecules
Takes more energy to to separate polar compound which means higher
boiling points
Stronger intermolecular forces in polar molecules than in similar
nonpolar molecules
Polar compounds have higher boiling points than nonpolar
compounds with smaller molar masses
Use similar masses to show better comparison between nonpolar
and polar
Polar should have higher boiling point
Hydrogen Bonding
Not a covalent bond
Type of dipole dipole interaction
Very strong
One element will always be hydrogen, the other will be a small element
with a very high electronegativity
Like nitrogen, fluorine, or oxygen
Trends
Normal trend
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