[CHEM 1212] - Final Exam Guide - Ultimate 24 pages long Study Guide!

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Published on 29 Mar 2017
School
KSU
Department
Chemistry
Course
CHEM 1212
KSU
CHEM 1212
FINAL EXAM
STUDY GUIDE
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Chapter 11.1-11.9 Liquids, Solids, and Intermolecular Forces
Properties of matter are determined by the properties of molecules and atoms
11.1 Water, No Gravity:
Intermolecular forces - Attractive forces that exist among the particles that compose
matter. The molecules attract other water molecules.
Intermolecular forces exist among all particles that compose matter.
The state of matter ( gas, solid, liquid) depends on the magnitude of the intermolecular
forces along with the amount of thermal energy.
Molecules composing matter are in constant random motion that are increased with the
amount of thermal energy.
Increasing thermal energy with intermolecular forces = gaseous; Decreasing thermal
energy with intermolecular forces = liquid or solid
11.2 Solids, Liquids, and Gases: A Molecular Comparison
Densities of solids and liquids are much greater than gases
For water, solids are slightly less dense than liquids. This is atypical behavior because
molecules move closer upon freezing (solids).
Ice however is a unique solid that is less dense than water because the unique crystal
structure results in water molecules moving slightly apart upon freezing.
Molecules closely spaced (solids and liquids) are not easily compressed, while
molecules widely spaced (gases) are highly compressible.
Solids can be crystalline - atoms are arranged in a well ordered 3D array - or amorphous
- atoms have no long range order.
Changed between states can be achieved by changing temperature and/or pressure.
High pressure = denser (solids). Lower pressure = less dense (gases)
11.3 Intermolecular Forces: The Forces that hold Condensed States Together
The structure that composes a substance determines the strength of the intermolecular
forces that hold the substance together which then determines the state of the
substance.
At room temperature
Solids and Liquids → Moderate to strong intermolecular forces (High Melting &
Boiling Points)
Gases → Weak intermolecular forces (Low Melting & Boiling Points)
Intermolecular forces originate from interactions among charges, partial charges, and
temporary charges.
Protons and electrons are attracted to one another because their potential energy
decreases as they get closer.
Intermolecular forces are much weaker than bonding forces.
Bonding forces are large charges at close distance.
Intermolecular forces are small charges acting at great distances.
To break O-H bonds in water (1000 degrees Celsius) but to break the intermolecular
cond (100 degrees Celsius) ← boiling point.
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Intermolecular forces include - dispersion forces, dipole-dipole forces, hydrogen
bonding, and ion-dipole forces.
All except ion-dipole forces can occur in all substances. Ion-dipole forces can only occur
in mixtures.
Dispersion Force (London Force):
Result from fluctuations in the electron distribution within molecules or atoms.
Atoms have dispersion forces because they have electrons. These electron can
at any moment, be unevenly distributed.
When charges deviate to one side allowing one side to be more negative or
positive this is called instantaneous dipole or temporary dipole.
The temporary dipole of a helium atom induces its neighbor to also have a
temporary dipole. Resulting attraction between + and - forces is called dispersion
force.
Magnitude of the dispersion force depends on how easily the electrons in the
atom or molecule can move or polarize in response to an instantaneous dipole,
depends on size/volume of the electron cloud.
A large electron cloud results in a greater dispersion force because electrons are
held tightly by the nucleus and polarize more easily.
At constant variables, dispersion force increases with increasing molar mass
(High molar mass = more electron dispersed).
However molar mass does not always correlate with magnitude of dispersion
force. Shape also matter
A long and larger surface area results in a higher boiling point. While a bulky,
round shape of a smaller area has a lower boiling point.
Dipole-dipole force:
Exists between all molecules that are polar.
Polar molecules have electron-rich regions (partial negative charge) and electron
deficient regions (partial positive charge).
Results in a permanent dipole where positive end of one dipole attracts
the negative end of another.
Polar molecules have higher melting and boiling points than nonpolar molecules.
ALL MOLECULES HAVE DISPERSION FORCES.
Polar molecules have additional dipole-dipole forces.
This raises their boiling and melting points relative to nonpolar molecules
with the same molar mass).
Boiling points increase with increasing dipole motion.
Polarity is also important in determining the miscibility - the ability to mix without
separating into two states of liquids. ( ie. polar liquids tend to be miscible with
water, while nonpolar liquids are not)
“Like - Like” mixes (ie. polar and polar or nonpolar and nonpolar)
Hydrogen Bonding:
Hydrogen bonding - Polar molecules containing Hydrogen bonded directly to
small electronegative atoms.
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Document Summary

Properties of matter are determined by the properties of molecules and atoms. Intermolecular forces - attractive forces that exist among the particles that compose matter. Intermolecular forces exist among all particles that compose matter. The state of matter ( gas, solid, liquid) depends on the magnitude of the intermolecular forces along with the amount of thermal energy. Molecules composing matter are in constant random motion that are increased with the amount of thermal energy. Increasing thermal energy with intermolecular forces = gaseous; decreasing thermal energy with intermolecular forces = liquid or solid. 11. 2 solids, liquids, and gases: a molecular comparison. Densities of solids and liquids are much greater than gases. For water, solids are slightly less dense than liquids. This is atypical behavior because molecules move closer upon freezing (solids). Ice however is a unique solid that is less dense than water because the unique crystal structure results in water molecules moving slightly apart upon freezing.