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Chapter 11

Chapter 11


Department
Chemistry
Course Code
CHMA11H3
Professor
Jamie Donaldson
Chapter
11

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Chemistry A11 Reactions and Mechanisms
Chapter 11
Section 11.1 Climbing and Intermolecular Forces
When thermal energy is high relative to intermolecular forces, matter tends to be gaseous.
When thermal energy is low relative to intermolecular forces, matter tends to be liquid or
solid
Section 11.2 Solids, Liquids, and Gases: A Molecular Comparison
The densities of the solid and liquid states are much greater than the densities of the gas
state
Waters solid state (ice) exhibits atypical behaviour, because most solids are slightly denser
than their corresponding liquids because the molecules move closer together upon freezing.
Liquids are not easily compressed because the molecules or atoms that compose them are
already in close contact
The molecules in a gas have a great deal of space between them and are easily forced into
smaller volume by an increase in external pressure.
solids may be crystalline, in which case the atoms or molecules that compose them are
arranged in a well ordered three-dimensional array
solids may be amorphous, in which case the atoms or moles that compose them have no
long-range order
we can transform one state of matter to another by changing the temperature, pressure, or
both
-the most common example of this phenomenon occurs in liquid petroleum, the propane
in the tank you buy is under extreme pressure and is therefore a liquid
Section 11.3 Intermolecular Forces: The Forces That Hold Condensed States Together
The strength of the intermolecular forces between the molecules or atoms that compose a
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substance determines its state.
Intermolecular forces originate from the interactions between charges, partial charges, and
temporary changes on molecules.
Protons and electrons are attracted to each other because their potential energy decreases as
they get closer together.
Molecules with partial or temporary charges are attracted to each other because their
potential energy decreases as they get closer together
Intermolecular forces are the result of smaller charges interacting at greater distances
The larger the distances between molecules, as well as the smaller charges involved result in
weaker forces
Dispersion Forces (also called London Forces) are the result of fluctuations in the electron
distribution within molecules or atoms
-the brief charge separation is known as instantaneous dipole or a temporary dipole
The 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, which in turn depends
on the size of the electron.
A larger electron cloud results in a greater dispersion force because the electrons are held
less tightly by the nucleus and therefore polarize more easily
-the dispersion force increases with increasing molar mass
Molecular shape and other factors must always be considered in determining the magnitude
of dispersion forces
Dipole-Dipole Forces exist in all molecules that are polar, polar molecules have
permanent dipoles that interact with the permanent dipoles of neighbouring molecules.
This additional attractive force raises their melting points relative to nonpolar molecules of
similar molar mass
Miscibility, is the ability to mix without separating into two states
Polar moles containing hydrogen atoms bonded to small electronegative atoms (fluorine,
oxygen, or nitrogen) exhibit the intermolecular force called hydrogen bonding
-the hydrogen bond, a super dipole-dipole force, occurs between the H atom on one
molecule and the F, O, or N on it neighbour.
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HYDROGEN BONDS SHOULD NOT BE CONFUSED WITH CHEMICAL BONDS
In general, boiling points increase with increasing molar mass, as expected based on
increasing dispersion forces
The ion-dipole force, occurs when an ionic compound is mixed with a polar compound, they
are the strongest of the types of intermolecular forces discussed here
11.4 Intermolecular Forces in Action: Surface Tension, Viscosity, and Capillary Action
Surface tension, the tendency of liquids to minimize their surface area, and is defined as
the energy required to increase the surface area by a unit amount
In order to increase the surface area of the liquid, molecules from the interior have to be
moved to the surface
Since molecules at the surface have a higher potential energy than molecules in the interior,
movement of interior molecules to the surface requires energy
-due to the energy requirement, liquids tend to try and minimize their surface area
Surface tension decreases as intermolecular forces decreases
A sphere is the geometrical shape with the smallest surface area to volume ratio
-the formation of a sphere minimizes the number of molecules at the surface,
minimizing the potential energy of the system
Viscosity, is the resistance of a liquid to flow
Viscosity is greater in substances with stronger intermolecular forces because id molecules
are more strongly attracted to each other, they do not flow around each other as freely
-there is an increase in viscosity with increasing molar mass (increasing potential for
dispersion forces)
-also we observe an increase in viscosity with increasing molecular length
Thermal energy partially overcomes the intermolecular forces, allowing molecules to flow
past each other more easily
Capillary action, is the ability of a liquid to flow against gravity up a narrow tube
Capillary action results from a combination of two forces: cohesive forces and adhesive forces
If the adhesive forces are greater than the cohesive forces, the attraction to the surface draws
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