CHEM REVIEWER
INTERMOLECULAR FORCES AND LIQUIDS AND SOLIDS
KINETIC MOLECULAR MODEL
explain the properties of
LIQUID SOLID
• Surface Tension Amorphous Crystalline
• Viscosity have particles held together by
• lonic
• Vapor pressure • Molecular
• Intermolecular Forces
• Boiling point • Dipole-dipole forces • Metallic
• Heat of • lon-dipole forces • Network
vaporization • Dispersion forces • Group 8A
• Hydrogen bonds
Kinetic Molecular Theory INTERMOLECULAR FORCES OF ATTRACTION
➢ Kinetic - Kinetos (Greek word) which
means “Movable” • This force holds
➢ It explains the properties of solids, liquids, the molecules
and gas in terms of intermolecular forces of together which can
attraction and the kinetic energy of the be attractive or
individual particles. repulsive.
• The attractions between molecules are not nearly as
strong as the intramolecular attractions (bonds)
that hold compounds together.
• Many physical properties reflect intermolecular
forces, like boiling points, melting points,
viscosity, surface tension, and capillary action.
TYPES OF INTERMOLECULAR FORCE
Weakest to strongest forces:
➢ Dispersion forces (or London dispersion forces)
➢ Dipole–dipole forces
➢ Hydrogen bonding (a special dipole–
dipole force)
• Strongly attracted to each • Weakly attracted to each
➢ Ion–dipole forces
other other; break their interaction Note: The first two types are also referred to
• Vibrate a little, but not easily collectively as Van der Waals forces.
much compared to liquids and • Vibrate and move more than
gases those in a solid
• Vibrate faster when heated • Move faster when heated
, FACTORS WHICH AFFECT AMOUNT OF DISPERSION FORCE IN • The boiling point of a liquid is the temperature
A MOLECULE at which its vapor pressure equals atmospheric
• Number of electrons in an atom (more electrons, more
pressure.
dispersion force)
• Size of atom or molecule/molecular weight
• The normal boiling point is the temperature at
• Shape of molecules with similar masses (more compact, which its vapor pressure is 760 torr.
less dispersion force) • The natural log of the vapor pressure of a liquid
is inversely proportional to its temperature. This
relationship is quantified in the Clausius–Clapeyron
equation.
CAPILLARY ACTION
➢ The rise of liquids up narrow tubes is called
capillary action.
➢ Adhesive forces attract the liquid to the wall
of the tube.
POLARIZABILITY & BOILING POINT ➢ Cohesive forces attract the liquid to itself.
• If something is easier to polarize, it has a lower
➢ Water has stronger adhesive forces with
boiling point. Remember: This means less
intermolecular force (smaller molecule: lower
glass; mercury has stronger cohesive forces with
molecular weight, fewer electrons). itself.
SURFACE TENSION
LIQUID CRYSTALS
➢ Water acts as if it has a “skin” on it due to ➢ Some substances do not go
extra inward forces on its surface. Those forces directly from the
are called the surface tension. solid state to the liquid state.
➢ In this intermediate state, liquid crystals have
VISCOSITY
➢ Resistance of a liquid to flow is some traits of solids and some of liquids.
called viscosity. ➢ Molecules in liquid crystals have some degree
• It is related to the ease with which of order.
molecules can move past each other. ➢ In nematic liquid crystals, molecules are only
• Viscosity increases with stronger intermolecular ordered in one dimension, along the long axis.
forces and decreases with higher temperature.
➢ In smectic liquid crystals, molecules are
VAPOR INCREASES ordered in two dimensions, along the long axis
➢ At any temperature, some liquid molecules and in layers.
have enough energy to escape the surface and
➢ In cholesteryic liquid crystals, nematic-like
become a gas.
crystals are layered at angles to each other.
➢ As the temperature rises, the fraction of
molecules that have enough energy to break WATER
free increases. It is usually referred to as the universal solvent.
• As more molecules escape the liquid, The structure/placement of its particles allows it
the pressure they exert increases. to take the shape of the container. It has the
• The liquid and vapor reach a state of ability to dissolve substances such as sugar and
dynamic equilibrium: liquid molecules salt.
evaporate, and vapor molecules condense at
the same rate.
INTERMOLECULAR FORCES AND LIQUIDS AND SOLIDS
KINETIC MOLECULAR MODEL
explain the properties of
LIQUID SOLID
• Surface Tension Amorphous Crystalline
• Viscosity have particles held together by
• lonic
• Vapor pressure • Molecular
• Intermolecular Forces
• Boiling point • Dipole-dipole forces • Metallic
• Heat of • lon-dipole forces • Network
vaporization • Dispersion forces • Group 8A
• Hydrogen bonds
Kinetic Molecular Theory INTERMOLECULAR FORCES OF ATTRACTION
➢ Kinetic - Kinetos (Greek word) which
means “Movable” • This force holds
➢ It explains the properties of solids, liquids, the molecules
and gas in terms of intermolecular forces of together which can
attraction and the kinetic energy of the be attractive or
individual particles. repulsive.
• The attractions between molecules are not nearly as
strong as the intramolecular attractions (bonds)
that hold compounds together.
• Many physical properties reflect intermolecular
forces, like boiling points, melting points,
viscosity, surface tension, and capillary action.
TYPES OF INTERMOLECULAR FORCE
Weakest to strongest forces:
➢ Dispersion forces (or London dispersion forces)
➢ Dipole–dipole forces
➢ Hydrogen bonding (a special dipole–
dipole force)
• Strongly attracted to each • Weakly attracted to each
➢ Ion–dipole forces
other other; break their interaction Note: The first two types are also referred to
• Vibrate a little, but not easily collectively as Van der Waals forces.
much compared to liquids and • Vibrate and move more than
gases those in a solid
• Vibrate faster when heated • Move faster when heated
, FACTORS WHICH AFFECT AMOUNT OF DISPERSION FORCE IN • The boiling point of a liquid is the temperature
A MOLECULE at which its vapor pressure equals atmospheric
• Number of electrons in an atom (more electrons, more
pressure.
dispersion force)
• Size of atom or molecule/molecular weight
• The normal boiling point is the temperature at
• Shape of molecules with similar masses (more compact, which its vapor pressure is 760 torr.
less dispersion force) • The natural log of the vapor pressure of a liquid
is inversely proportional to its temperature. This
relationship is quantified in the Clausius–Clapeyron
equation.
CAPILLARY ACTION
➢ The rise of liquids up narrow tubes is called
capillary action.
➢ Adhesive forces attract the liquid to the wall
of the tube.
POLARIZABILITY & BOILING POINT ➢ Cohesive forces attract the liquid to itself.
• If something is easier to polarize, it has a lower
➢ Water has stronger adhesive forces with
boiling point. Remember: This means less
intermolecular force (smaller molecule: lower
glass; mercury has stronger cohesive forces with
molecular weight, fewer electrons). itself.
SURFACE TENSION
LIQUID CRYSTALS
➢ Water acts as if it has a “skin” on it due to ➢ Some substances do not go
extra inward forces on its surface. Those forces directly from the
are called the surface tension. solid state to the liquid state.
➢ In this intermediate state, liquid crystals have
VISCOSITY
➢ Resistance of a liquid to flow is some traits of solids and some of liquids.
called viscosity. ➢ Molecules in liquid crystals have some degree
• It is related to the ease with which of order.
molecules can move past each other. ➢ In nematic liquid crystals, molecules are only
• Viscosity increases with stronger intermolecular ordered in one dimension, along the long axis.
forces and decreases with higher temperature.
➢ In smectic liquid crystals, molecules are
VAPOR INCREASES ordered in two dimensions, along the long axis
➢ At any temperature, some liquid molecules and in layers.
have enough energy to escape the surface and
➢ In cholesteryic liquid crystals, nematic-like
become a gas.
crystals are layered at angles to each other.
➢ As the temperature rises, the fraction of
molecules that have enough energy to break WATER
free increases. It is usually referred to as the universal solvent.
• As more molecules escape the liquid, The structure/placement of its particles allows it
the pressure they exert increases. to take the shape of the container. It has the
• The liquid and vapor reach a state of ability to dissolve substances such as sugar and
dynamic equilibrium: liquid molecules salt.
evaporate, and vapor molecules condense at
the same rate.
