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8/14/2019 Condensed Phases - Liquids and Solids
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2/23/2010
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Chemistry 8ed, Whitten etal, TB/C 2007
Solids and liquids areSolids and liquids are condensed statescondensed states..
their atoms, ions, or molecules are much closertheir atoms, ions, or molecules are much closerto one another than in gases.to one another than in gases.
are highly incompressible.are highly incompressible.
The intermolecular forces of attractionsintermolecular forces of attractions ininliquids and solids are strongliquids and solids are strong..
Chemistry 8ed, Whitten
etal, TB/C 2007
Schematic representation of the threecommon states of matter.
Chemistry 8ed, Whitten
etal, TB/C 2007
If we compare the strengths ofstrengths of
interactionsinteractions among particles and thedegree of orderingdegree of ordering of particles, we seethat
Gases< Liquids < Solids
Chemistry 8ed, Whitten
etal, TB/C 2007
forces between individual particles
(atoms, molecules, and ions) of asubstance
Ion-ion interaction
Dipole-dipole
H-bonding London forces or Dispersion forces
Chemistry 8ed, Whittenetal, TB/C 2007 6
the force of attraction between twooppositely charged ions
is governed by Coulombs law
Chemistry 8ed, Whittenetal, TB/C 2007
Ion-ion interaction
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Coulombs law determines:
the melting and boiling points of ionic compounds
the solubility of ionic compounds.
Ionic substances containing multiply charged ions, (egAl3+ , Mg2+ , O2- , S2- ) usually have higher melting/boiling
points than singly charged ions
For a series of ions of s imilar charge, the closer approachof smaller ions results in stronger interionic attractionsand consequently higher melting/boiling properties
Chemistry 8ed, Whitten
etal, TB/C 2007
Ion-ion interaction
table of melting points
Melting Points of Some Ionic Compounds
Compound Mp (o C) Compound Mp (o C) Compound Mp (o C)
NaF 993 CaF2 1423 MgO 2800
NaCl 801 Na2 S 1180 CaO 2580
NaBr 747 K2 S 840 BaO 1923
Chemistry 8ed, Whitten
etal, TB/C 2007
Ion-ion interaction
9
the force of attraction between two
polar molecules
Example: BrF (a polar molecule)
Chemistry 8ed, Whitten
etal, TB/C 2007
Dipole-dipole interactions
10
also a force of attraction between two polar
molecules BUT ONLY APPEARS IN
MOLECULES HAVING A HYDROGEN ATOM
ATTACHED TO N, O, F (the three
electronegative atoms).
Chemistry 8ed, Whitten
etal, TB/C 2007
Hydrogen-bonding
11
- also called London forces and are very weak
forces
- this is the only attractive force in nonpolarmolecules
- occurs only in extremely short distances,i.e. 1/d7
Chemistry 8ed, Whittenetal, TB/C 2007
Dispersion forces
12
Consider He as an isolated atom. In a group of He atoms, the temporary dipole in one
atom induces other atomic dipoles.
Chemistry 8ed, Whittenetal, TB/C 2007
Dispersion forces
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Similar effects occur in a group of I2
molecules.
Chemistry 8ed, Whitten
etal, TB/C 2007
Dispersion forces
Induced dipole- induced dipole interaction
Interaction strictly between nonpolarmolecules
Dipole-induced dipole (originally, this is notconsidered as London forces) Interaction between a dipole (polar) molecule
and a nonpolar molecule
Chemistry 8ed, Whitten
etal, TB/C 2007
Dispersion forces
are most important when POLARIZABILITY is
high:
high # of electrons (SQUISHY MOLECULE)
appearance of delocalized bonds (that actuallymakes the molecule FLAT due to sp2 and sp3
hybrid)
overall molecule is LARGE
molecule covers a larger area
Chemistry 8ed, Whitten
etal, TB/C 2007
Dispersion forces
in general, the trend for IMFA strength is:
ion-ion> {ion-dipole}
> H-bonding> dipole-dipole
> London dispersion{dipole - induced dipole > induced dipole -
induced dipole}
Chemistry 8ed, Whitten
etal, TB/C 2007
A molecule may have MORE THAN ONETYPE OF IMFA when it interacts with similarmolecules.
When comparing properties, it is best tolook at the OVERALL NET EFFECT OF THEEXISTING IMFA for the molecule as it acts inthe ENTIRE SUBSTANCE (not just betweentwo molecules).
Chemistry 8ed, Whittenetal, TB/C 2007 18
AMORPHOUS & CRYSTALLINE
Amorphous solids do not have a well ordered molecularstructure.
Examples include waxes, glasses, asphalt.
Crystalline solids have well defined structures that consistofextended array of repeating units called unit cellsunit cells.
Crystalline solids display X-ray diffraction patternswhich reflect the molecular structure.
Properties at the Solid State
Chemistry 8ed, Whittenetal, TB/C 2007
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AMORPHOUS & CRYSTALLINE
Chemistry 8ed, Whitten
etal, TB/C 2007
Properties at the Solid State
UNIT CELLS
are the smallest repeating unit of a crystal
Properties at the Solid State
Chemistry 8ed, Whitten
etal, TB/C 2007
Chemistry 8ed, Whitten
etal, TB/C 2007
Properties at the Solid State
There are seven basic crystal systems.
Chemistry 8ed, Whitten
etal, TB/C 2007
Properties at the Solid State
There are four types of unit cell.- primitive - face centered- body centered - side centered
According to Bond between Particles
Molecular SolidsMolecular Solids Network CovalentNetwork Covalent
Ionic solidsIonic solids Metallic SolidsMetallic Solids
Chemistry 8ed, Whittenetal, TB/C 2007
Properties at the Solid State Molecular Solids have molecules in each of the positions of the unit
cell
have low melting points, are volatile, and areelectrical insulators.
Examples: water, sugar, carbon dioxide, benzene
Chemistry 8ed, Whittenetal, TB/C 2007
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Network Covalent Solids have atoms that are covalently bonded to one
another
Examples: Diamond, graphite, SiO2 (sand), SiC
Chemistry 8ed, Whitten
etal, TB/C 2007
Ionic Solids have ions that occupy the positions in the unit cell
Examples: CsCl, NaCl, ZnS
Chemistry 8ed, Whitten
etal, TB/C 2007
Metallic Solids
may be thought of as positively charged nucleisurrounded by a sea of electrons.
the positive ions occupy the crystal lattice positions.
Examples: Na, Li, Au, Ag
Chemistry 8ed, Whitten
etal, TB/C 2007
Melting PointMelting Point
the temperature at which the solid form
of a substance is at equilibrium with its
liquid state
normal melting point is the
temperature at which the solid melts atexactly 1.00 atm of pressure
Properties at the Solid State
Chemistry 8ed, Whitten
etal, TB/C 2007
Properties at the Solid State
SublimationSublimation
process where the solidtransforms directly to thevapor phase withoutpassing through theliquid phase
solid CO2 or dry icedoes this well
Chemistry 8ed, Whittenetal, TB/C 2007 30
ViscosityViscosity
the resistance to flow
compare how waterpours out of a glasscompared to molasses,syrup or honey
Chemistry 8ed, Whittenetal, TB/C 2007
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Surface TensionSurface Tension
is a measure of theunequal attractionsthat occur at thesurface of a liquid the molecules at the
surface are attractedunevenly
Chemistry 8ed, Whitten
etal, TB/C 2007 32
Capillary ActionCapillary Action
is the ability of aliquid to rise (or fall)
in a glass tube orother container
affects meniscus ofliquids
Chemistry 8ed, Whitten
etal, TB/C 2007
33
Cohesive forces are the forces that hold
liquids together.
Adhesive forces are the forces between aliquid and another surface.
Capillary rise implies that the:
Adhesive forces > cohesive forces Capillary fall implies that the:
Cohesive forces > adhesive forces
Chemistry 8ed, Whitten
etal, TB/C 2007 34
Water exhibits a capillary rise. Mercury exhibits a capillary fall.
Chemistry 8ed, Whitten
etal, TB/C 2007
35
EvaporationEvaporation
the process in which molecules escape fromthe surface of a liquid and become a gas; is
temperature dependent.
Chemistry 8ed, Whittenetal, TB/C 2007 36
Boiling PointBoiling Point
is the temperature at which the liquids vaporpressure is equal to the applied pressure normal boiling point is the boiling point
when the pressure is exactly 1 atm
Distillation is a method we use to separatemixtures of liquids based on theirdifferences in boiling points.
Chemistry 8ed, Whittenetal, TB/C 2007
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Vapor PressureVapor Pressure
is the pressure exerted by a liquids vaporon its surface at equilibrium.
Vapor Pressure (torr) and boiling point for threeliquids at different temperatures.
0oC 20oC 30oC normal boiling point
diethyl ether 185 442 647 36oCethanol 12 44 74 78oCwater 5 18 32 100oC
Chemistry 8ed, Whitten
etal, TB/C 2007 38
Vapor Pressure as a function of temperature.
Chemistry 8ed, Whitten
etal, TB/C 2007
IMFA strength leads to Higher melting point
Higher boiling point
Lower vapor pressure
Lower evaporation rate Stronger surface tension
Higher viscosity
Chemistry 8ed, Whitten
etal, TB/C 2007
Comparing substances atcondensed state
40Chemistry 8ed, Whitten
etal, TB/C 2007
Comparing boiling point ofsubstances at condensed state
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