Liquids and Solids
Properties of Liquids and the KineticMolecular Theory
• Liquid- is a form of matter that has a definite
volume and takes the shape of its container. The
particles are in constant motion.
• The intermolecular forces in liquids can be dipoledipole, London dispersion, and hydrogen bonding.
• The Kinetic-Molecular Theory states that particles
of a liquid have no fixed space, and move about
constantly.
• Fluid-is a substance that can flow and takes the
shape of its container- used for liquids and gases
both
(Showing meting of ice and changes in molecular structure)
http://mutuslab.cs.uwindsor.ca/schurko/animations/waterphases/status_water.htm
Liquid’s molecular structure
http://www.media.pearson.com.au/schools/cw/au_sch_whalley_sf1_1/int/matter.html
(magnification at molecular level from ice to water)
Properties of Liquids
Relatively High
Density
The liquids are very dense because the particles of
liquids are extremely close together. Also, different
liquids have different densities.
Relative
Liquids are much less compressible because they have
Incompressibility tightly packed particles, and also transmit pressure
equally.
Ability to Diffuse The liquids diffuse with most liquids, but at a slower
rate than gases because the particles are more tightly
packed, and there are many attractive forces between
the particles.
Intermolecular Forces:Van Der Waals
Forces
• Significant in molecular substances (gases,
most liquids and solids that are molecular)
• Strong intermolecular forces lead to
increased m.p. and b.p.
• What are some properties of molecular
substances? (nonconductors, insoluble in
water, but soluble in most non polar
solvents)
http://www.wwnorton.com/COLLEGE/chemistry/gilbert/tutorials/interface.asp?ch
apter=chapter_09&folder=intermolecular_forces
(ion-ion, ion- dipole, dipole-dipole tutorial)
LDFs
-temporary dipole interactions and are the weakest intermolecular
bonds
-present between all molecules and non bonded atoms, and are
significant in noble gas atoms and non polar compounds.
-The strength of LDFs depends upon two things:
1. # of e in atoms that make up the molecule
2. The ease with which e are dispersed to form temporary dipoles.
http://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml
Dipole-Dipole, LDFs animation
Dipole-Dipole Interactions
• Found in PC
molecules. Stronger
than LDFs
• LDFs and DipoleDipole are also called
as Van Der Waals
forces
• Ex: ICl
H Bonds
• When H is bonded to a
relatively small,
electronegative atom,
such as N,O, or F
• Strongest of the weak
interactions (strongest
intermolecular forces)
Properties of Liquids: Surface
Tension
http://www.visionlearning.com/library/module_viewer.php?mid=57
Water Strider Video
Surface Tension and Capillary
Action
http://www.wwnorton.com/COLLEGE/chemistry/gilbert/tutorials/interface.asp?chapter=chapter_09&folde
r=capillary_action
(Capillary, Surface tension Tutorial)
Surface Tension-a force that tends to pull adjacent parts of a
liquid’s surface together, thereby decreasing surface area
to the smallest possible size.
~The higher the attraction forces (intermolecular forces), the
higher the surface tension. Surface tension causes liquid
droplets to take a spherical shape.
Capillary action- the attraction of the surface of a liquid to
the surface of a solid.
~Capillary action is the reason water from the roots of a tree
goes to the leaves. It is also responsible for the liquid
surface called the meniscus.
Surface Tension
• The surface of any liquid behaves as if it was a
stretched membrane. This phenomenon is known
as surface tension
• Surface tension is caused by intermolecular forces
at the liquid’s interface with a gas or a solid.
• Surface tension depends on the nature of the
liquid, the surrounding media and temperature.
• Liquids that have strong intermolecular forces will
have higher values of surface tension than liquids
that have weak intermolecular forces.
http://citt.ufl.edu/Marcela/Sepulveda/html/en_tension.htm
Viscosity
• Defined as “resistance to flow” of a fluid.
• Viscous liquids move slower.
• The greater the intermolecular forces the
more is the viscosity.
http://plc.cwru.edu/tutorial/enhanced/lab/visco/intro/intro.htm (Viscosity
and molecular size interactive simulation)
http://www.youtube.com/watch?v=7Ft9VDDPWb4&feature=related
(video on different density liquids)
Physical Properties of Water
• Highest density at 4 degrees celsius. Ice is one of
the few solids to have a lower density in solid
phase as compared to liquid phase. This property
is very useful in ice skating, and fishes in lakes
etc.
• Because of H Bonding water has a much higher
b.p. and m.p.as compared to other liquids. This
property is making water one of the best coolants.
• ( Ex: Perspiration, In car radiators etc)
http://www.wwnorton.com/COLLEGE/chemistry/gilbert/tutorials/chapter_09/water_h_bond/in
dex.html
(Water and Ice at molecular level)
Liquid- Vapor Equilibrium
• Vapor Pressure: The pressure exerted on the
surface of a liquid by the vapor that is in
equilibrium with the liquid is called as “vapor
pressure”
• Once equilibrium between a liquid and vapor is
reached, the number of molecules per unit volume
in a vapor does not change with time. Hence, the
vapor pressure over the liquid remains constant at
a given temperature.
• Vapor Pressure is independent of the volume of
the container. Why?
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swf
(vapor pressure equilibrium on manometer)
Vapor Pressure Vs. Temperature
Vapor pressure increases with the increase in
temperature.
http://hogan.chem.lsu.edu/matter/chap26/animate3/an26_034.mov
(VP vs Temp)
Evaporation
Vaporization-the process by which a liquid or solid
changes to gas.
Evaporation- is the process where particles escape
from the surface of a non boiling liquid and enters
the gas state.
~Evaporation takes place because the particles of
liquids have different kinetic energies, therefore
some of the particles with higher kinetic energy
overcome the intermolecular forces and evaporate
to go in the gas phase.
Boiling
Boiling- is the change of a liquid to bubbles or vapor. Boiling
occurs when the vapor pressure becomes equals
atmospheric pressure.
• A liquid boils at the temp. at which its vapor
pressure is equal to the pressure above its
surface. (usually atmospheric pressure)
• If the pressure above the liquid’s surface is 1 atm,
then this temperature is called as its “Normal
Boiling Point”
• B.P. of a liquid is reduced by lowering the
pressure above it.
• Why does it take longer to cook at high altitudes?
Boiling: A liquid boils at a temp. when the vapor
pressure P1 becomes equal to the external pressure
P2 above the liquid
Phase Changes
• Melting(fusion)/Freezing
• Vaporization/Condensation
• Sublimation/Deposition
http://hogan.chem.lsu.edu/matter/chap26/animate3/an26_035.mov
(s-l-g with molecular motion at phase change)
Time Temperature Curve
1 & 3 H = m * DT * Cp
2&4
H = m * DHvap
100
Boiling
Condensation
T
Melting(Fusion)
0
1
Freezing
2
3
Time ( heat energy added )
4
Solids
High
Density
and
Incompre
ssibility
~Solids are much more dense than liquids or
gases because their particles are so much
closer together.
~Solids are also less compressible than
liquids, and are mostly thought of as not
compressible at all.
Types of Solids
• Solids are of two types:
• Crystalline solids- consist of crystals which
are substances which are organized in
symmetric, geometric ways.
• Amorphous solids-non crystalline solid
where the particles are arranged randomly.
Differences between Amorphous
and Crystalline Solids
Crystalline Solids
Exist either as single
crystals or group of
crystals fused
together.The total three
dimensional arrangement
of particles is called as
crystal structure.
Crystalline solids can be of
four types:
Ionic, Covalent Network,
Metallic and Covalent
Crystals
Amorphous Solids
Unlike crystalline solids,
amorphous solids do not
have a regular shape.
Amorphous solids are
formed when liquids are
cooled gradually, so
particles are not arranged
in any particular order.
Ex: Plastic, Glasses
Crystalline Solids
• There are four types of crystals:
• 1. Ionic crystals: The positive and negative ions crystals have
properties: high melting points, are hard and brittle, and good
insulators.
• 2. Covalent network crystals: the sites have single atoms. They are
nonconductors or semiconductors and have high melting points. Ex:
Graphite, diamond
• 3. Metallic crystals: these are metal atoms with a sea of valence
electrons. There is high electric conductivity of metals, and the
melting points differ. Ex: Iron, Aluminum etc
• 4. Covalent molecular crystals: they are held together by covalent
forces, and have low melting points, are easily vaporized, soft, and
good insulators. Ex: Sugar, Dry Ice
Pictures of Solids: http://ull.chemistry.uakron.edu/genobc/Chapter_06/
Crystalline Solids
Covalent
Network:
Diamond
Covalent Network: Graphite
http://www.wwnorton.com/COLLEGE/chemistry/gilbert/tutorials/interface.asp?chapter=chapter_09&folder=phase_diagrams
Tutorial on phase diagram with phase changes
CHANGES IN STATE
Liquid
1 atm
P
Solid
O
Gas
T, in C
100