The key differences between the states of matter are the distances between particles and the strength of intermolecular forces. In solids and liquids, particles are closer together due to stronger intermolecular forces. The state of a substance depends on a balance between kinetic energy of particles and the attractions between them. There are various types of intermolecular forces including hydrogen bonding, dipole-dipole interactions, and dispersion forces. The strength of these forces influences many physical properties such as boiling point, viscosity, and surface tension.
3. Because in the solid and liquid states particles
are closer together, we refer to them as
condensed phases.
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4. The state a substance is
in at a particular
temperature and
pressure depends on two
antagonistic entities:
◦ The kinetic energy of the
particles
◦ The strength of the
attractions between the
particles
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5. intramolecular force
is any force that holds together the atoms making
up a molecule or compound. They contain all types
of chemical bond. They are stronger than
intermolecular forces, which are present between
atoms or molecules that are not actually bonded.
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6. Intermolecular forces
are forces of attraction or repulsion which act
between neighboring particles (atoms, molecules
or ions). They are weak compared to the
intramolecular forces, the forces which keep a
molecule together
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7. Attraction between 2 oppositely charged ions
◦ Ions - charged atoms
◦ formed by
transferring e-
from a metal
to a nonmetal
9. Attraction between neutral atoms
◦ formed by sharing e- between two nonmetals.
◦ A covalent bond is a chemical bond that involves the
sharing of electron pairs between atoms. The stable balance
of attractive and repulsive forces between atoms when they
share electrons is known as covalent bonding.
14. The attractions between molecules are not
nearly as strong as the intramolecular
attractions that hold compounds together.
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15. They are, however, strong enough to control
physical properties such as boiling and
melting points, vapor pressures, and
viscosities.
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17. Van der Waals forces' is a general term used
to define the attraction of
intermolecular forces between molecules. There
are two kinds of Van der Waals forces: weak
London Dispersion Forces and stronger dipole-
dipole forces.
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19. A fourth type of force, ion-dipole interactions
are an important force in solutions of ions.
The strength of these forces are what make it
possible for ionic substances to dissolve in
polar solvents.
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21. Molecules that have
permanent dipoles are
attracted to each other.
◦ The positive end of one is
attracted to the negative
end of the other and vice-
versa.
◦ These forces are only
important when the
molecules are close to
each other.
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22. The more polar the molecule, the higher is its
boiling point.
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23. While the electrons in the 1s orbital of helium
would repel each other (and, therefore, tend
to stay far away from each other), it does
happen that they occasionally wind up on the
same side of the atom.
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24. At that instant, then, the helium atom is
polar, with an excess of electrons on the left
side and a shortage on the right side.
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25. Another helium nearby, then, would have a
dipole induced in it, as the electrons on the
left side of helium atom 2 repel the electrons
in the cloud on helium atom 1.
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26. London dispersion forces, or dispersion
forces, are attractions between an
instantaneous dipole and an induced dipole.
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27. These forces are present in all molecules,
whether they are polar or non polar.
The tendency of an electron cloud to distort
in this way is called polarizability.
Polarizability is the ability for a molecule to
be polarized. It is a property of matter
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28. The shape of the molecule affects
the strength of dispersion forces:
long, skinny molecules (like n-
pentane tend to have stronger
dispersion forces than short, fat
ones (like neopentane).
This is due to the increased
surface area in n-pentane.
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29. The strength of dispersion forces tends to
increase with increased molecular weight.
Larger atoms have larger electron clouds,
which are easier to polarize.
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30. The dipole-dipole interactions
experienced when H is bonded to
N, O, or F are unusually strong.
We call these interactions
hydrogen bonds.
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32. The strength of the
attractions between
particles can greatly
affect the properties
of a substance or
solution.
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33. 33
Properties of Liquids
Surface tension is the amount of energy required to stretch or increase the
surface of a liquid by a unit area.
Strong
intermolecular
forces
High surface
tension
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34. Resistance of a liquid
to flow is called
viscosity.
It is related to the ease
with which molecules
can move past each
other.
Viscosity increases
with stronger
intermolecular forces
and decreases with
higher temperature.
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35. Surface tension
results from the net
inward force
experienced by the
molecules on the
surface of a liquid.
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37. 37
Properties of Liquids
Cohesion is the intermolecular attraction between like molecules
Adhesion is an attraction between unlike molecules
Adhesion
Cohesion
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