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Solids and Liquids
Physical Properties of
Liquids
2 16.4 Physical Properties of Liquids
Condensed matter:Atoms or molecules are closely packed and interact with each other
Atoms or molecules do not interact with each other, except for collisions
3 16.4 Physical Properties of Liquids
Liquids have a permanent network
of intermolecular bonds that are
continuously made and broken
liquids hold together
liquids can flow
4 16.4 Physical Properties of Liquids
flow: the ability of a liquid to move and change shape under a force, such as gravity.
5 16.4 Physical Properties of Liquids
On the molecular level, liquids are like amorphous solids.
Energy of solid vs. liquid
However, higher energy in liquids causes intermolecular bonds to break quickly after they are formed.
6 16.4 Physical Properties of Liquids
Quartz a crystalline form of SiO2
Glassan amorphous form of SiO2
Liquid SiO2 doesn’t remember whether it came from quartz or glass!
slow cooling fast cooling
7 16.4 Physical Properties of Liquids
Quartz a crystalline form of SiO2
Glassan amorphous form of SiO2
Liquid SiO2 doesn’t remember whether it came from quartz or glass!
melting melting
8 16.4 Physical Properties of Liquids
Cohesion
Physical properties
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
9 16.4 Physical Properties of Liquids
Cohesion
Cohesion keeps rain drops together as they fall on the ground
Liquid mercury (Hg) is very cohesive
10 16.4 Physical Properties of Liquids
Cohesion
Adhesion
Physical properties
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
11 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
12 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
13 16.4 Physical Properties of Liquids
Cohesion or adhesion?
Water is more adhesiveIt sticks to the sides of the glass
Mercury is more cohesiveIt sticks to itself more
Meniscus
14 16.4 Physical Properties of Liquids
Plants use capillary
action
to draw water up from roots to
leaves.
Even very tall trees move
water this way.
Water passes through these tubes
capillary action: an effect where liquids is pulled up a thin tube by adhesion
15 16.4 Physical Properties of Liquids
Cohesion
Adhesion
Viscosity
Physical properties
The resistance of a liquid to flow under an applied force
Honey
16 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.
17 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
18 16.4 Physical Properties of Liquids
Viscosity
Viscosity depends on the strength of intermolecular bondsthe shape of the molecules
Oils are more viscous because the long-chain molecules can be easily entangled, and this slows down the flow
19 16.4 Physical Properties of Liquids
Cohesion
Adhesion
Viscosity
Surface tension
Physical properties
A property of liquids to resist having their surface broken
20 16.4 Physical Properties of Liquids
surface tension: a property of liquids to resist having their surfaces broken, usually measured in J/m2.
Surface tension measures
the energy it takes to break the
surface of a liquid.
21 16.4 Physical Properties of Liquids
Surface tension
Soaps work by partially lowering 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
22 16.4 Physical Properties of Liquids
Cohesion
Adhesion
Viscosity
Surface tension
Liquids have a permanent network of intermolecular bonds that are continuously made and broken
This results in interesting physical properties: