[CHEM 1112] - Midterm Exam Guide - Comprehensive Notes for the exam (22 pages long!)

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7 Feb 2017
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GWU
CHEM 1112
MIDTERM EXAM
STUDY GUIDE
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Review of Intermolecular
Forces, Liquids, and Solids
The States of Matter
-fundamental difference between states of matter —> distance between particles
gas
-particles have freedom of motion
far apart from one another
-total disorder
liquid
-particles are clustered with one another and take shape of one another
-has extremely weak bonds or no bonds at all
-particles free to move relative to each other
close together
-disorder
solid
-particles in fixed positions
close together
-ordered arrangement
-solids and liquids = condensed phases
b/c particles are closer together
-substance’s state is in at a specific temperature depends on:
KE of particles
strength of attractions b/w particles
Intermolecular Forces
-intramolecular forces that hold compounds together are extremely stronger than intermolecular
attractions
intermolecular forces are strong enough to control physical properties (i.e. boiling and melting
points, vapor pressures, and viscosities)
-collectively known as van der Waals forces
van der Waals Forces
-dipole-dipole interactions
-hydrogen bonding
-London dispersion forces
Ion-Dipole Interactions
-important in ionic solutions
-strength makes it possible for ionic substances to dissolve in polar solvents
example: salt in water
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Dipole-Dipole Interactions
-molecules w/ permanent dipoles are attracted to each other
positive end of one is attracted to negative end of the other…..vice versa
-forces only important when molecules are close to each other
-more polar the molecule……the higher the boiling point
London Dispersion Forces
-attractions between an instantaneous dipole and induced dipole
present in all molecules whether polar or non polar
-polarizability
tendency of an electron to distort into instantaneous or induced dipole
example: 1s orbital of He
-electrons would repel each other and tend to be away form one another
on occasion….electrons are on the same side of the atom
-when this occurs He atom is polar w/ excess electrons on left side and shortage on
right side
another He atom nearby would then have a dipole induced in it
-electrons on left side of He atom #2 would repel electrons on He atom #1
Factors Affecting London Forces
-shape of molecule affects strength of dispersion forces
long, skinny molecules
-have stronger dispersion forces than short fat ones
due to increased surface area
-strength of dispersion forces increase with increased molecular weight
larger atoms have larger electron clouds that are easier to polarize
Hydrogen Bonding
-dipole-dipole interactions experienced when H bonds to N, O, or F
these bonds are very strong
-interactions = hydrogen bonds
-arises in part from high electronegativity of N, O, and F
hydrogen nucleus is exposed when bonded to these highly electronegative elements
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