Solids and
Liquids
Physical
Properties of
Liquids
Atoms or molecules do not interact with
each other, except for collisions
Condensed matter:
Atoms or molecules are closely packed
and interact with each other
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16.4 Physical Properties of Liquids
Liquids have a permanent network
of intermolecular bonds that are
continuously made and broken
liquids hold
together
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liquids
can flow
16.4 Physical Properties of Liquids
flow: the ability of a liquid to move and change shape
under a force, such as gravity.
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16.4 Physical Properties of Liquids
Energy of solid vs. liquid
On the molecular level, liquids are
like amorphous solids.
However, higher energy in liquids
causes intermolecular bonds to
break quickly after they are formed.
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16.4 Physical Properties of Liquids
Quartz
Glass
a crystalline form of SiO2
an amorphous form of SiO2
slow cooling
fast cooling
Liquid SiO2 doesn’t remember whether
it came from quartz or glass!
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16.4 Physical Properties of Liquids
Quartz
Glass
a crystalline form of SiO2
an amorphous form of SiO2
melting
melting
Liquid SiO2 doesn’t remember whether
it came from quartz or glass!
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16.4 Physical Properties of Liquids
Physical properties
Cohesion
The property of a liquid that
causes it to hold together
Attractive forces between
molecules in a liquid cause
liquid drops to come together as
tight as possible in a perfect sphere
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16.4 Physical Properties of Liquids
Cohesion
Cohesion keeps rain
drops together as they
fall on the ground
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Liquid mercury (Hg)
is very cohesive
16.4 Physical Properties of Liquids
Physical properties
Cohesion
Adhesion
The property of a liquid that
causes it to stick to surfaces
Geckos use the property of
adhesion to stick to surfaces
such as the walls and ceilings
of houses
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16.4 Physical Properties of Liquids
Adhesion
When something is “wet,”
we mean that liquid is adhering to it
Different surfaces have different wettability:
they can be wet by the same liquid differently
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16.4 Physical Properties of Liquids
Adhesion
When something is “wet,”
we mean that liquid is adhering to it
Different surfaces have different wettability:
they can be wet by the same liquid differently
Liquids that adhere to things very well
are called adhesives
They are commonly used as glues
or put onto tape to make it sticky
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16.4 Physical Properties of Liquids
Cohesion or adhesion?
Water is more adhesive
It sticks to the sides
of the glass
Mercury is more cohesive
It sticks to itself more
Meniscus
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16.4 Physical Properties of Liquids
Water passes through these tubes
Plants use capillary action
to draw water up from roots to
leaves.
Even very tall trees move
water this way.
capillary action: an effect where liquids is pulled up a thin
tube by adhesion
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16.4 Physical Properties of Liquids
Physical properties
Cohesion
Adhesion
Viscosity
The resistance of a liquid to
flow under an applied force
Honey
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16.4 Physical Properties of Liquids
Viscosity
Viscosity is a measure of resistance to flow.
Snails and slugs use mucus,
a very viscous substance,
to help them stick to
surfaces and move.
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16.4 Physical Properties of Liquids
Viscosity
Viscosity depends on the strength of intermolecular bonds
Water is a polar molecule with
strong intermolecular forces.
Water is more viscous than
nonpolar liquids, such as liquid
nitrogen
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16.4 Physical Properties of Liquids
Viscosity
Viscosity depends on the strength of intermolecular bonds
the shape of the molecules
Oils are more viscous because the long-chain molecules
can be easily entangled, and this slows down the flow
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16.4 Physical Properties of Liquids
Physical properties
Cohesion
Adhesion
Viscosity
Surface tension
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A property of liquids to resist
having their surface broken
16.4 Physical Properties of Liquids
Surface tension measures
the energy it takes to break the
surface of a liquid.
surface tension: a property of liquids to resist having their
surfaces broken, usually measured in J/m2.
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16.4 Physical Properties of Liquids
Surface tension
Soaps are medium-length
chains with
- one polar end
- and one non-polar end
The polar end adsorbs to the
water surface, and this breaks up
the surface tension
Soaps work by partially lowering surface tension
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16.4 Physical Properties of Liquids
Liquids have a permanent network of intermolecular bonds
that are continuously made and broken
This results in interesting
physical properties:
Cohesion
Adhesion
Viscosity
Surface tension
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16.4 Physical Properties of Liquids