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INTRODUCTORY
CHEMISTRY
Liquids and
Solids
(Ch
...
• We can study the liquid state and make 5 general
observations
...
Liquids have a variable shape, but a fixed
volume
...
Liquids usually flow readily
...
2
Properties of Liquids Continued
3
...
4
...
• Liquids are about 1000 times more dense than gases
...
Liquids that are soluble mix homogeneously
...
3
Review - Polar Covalent Bonds
• Covalent bonds result from the sharing of valence
electrons
...
• When one of the atoms holds the shared electrons
more tightly, the bond is polarized
...
4
Review - Electronegativity
• Each element has an innate ability to attract
valence electrons
...
• Fluorine is the most electronegative element
...
• The negatively charged atom is indicated by the
symbol δ–, and the positively charged atom is
indicated by the symbol δ+
...
δ+
H – Cl δ–
We can also draw the
dipole moment to
show polarity
Polar vs Nonpolar vs Ionic Bonds
We can compare electronegativities of two atoms to
determine what type of bond is present:
Electronegativity
Difference
Bond Type
Example
0 - 0
...
5 - 2
...
0+
ionic
NaCl
Nonpolar Covalent Bonds
Refer to the periodic table in Fig 12
...
a) I
Br
b) C
Se
c) H
Br
9
Intermolecular Bond Concept
• An intermolecular bond is an attraction between
molecules, whereas intramolecular bonds are between
atoms in a molecule
...
• Intermolecular bonds are much weaker than
intramolecular bonds
...
• This uneven distribution of electrons in a molecule
is called a dipole
...
11
Intermolecular Bonds Cont’d
There are three types of intermolecular forces:
1
...
Dipole forces
3
...
• Electrons are constantly shifting and a region may
become temporarily electron poor and slightly
positive while another region becomes slightly
negative
...
13
Dispersion Forces
• The electrons are in constant motion
• For brief periods of time, the electrons
are concentrated on one side of the
molecule
...
• Very brief charge differences in the
molecule attract other molecules around
it due to this temporary dipole
...
• These forces are very weak for
small molecules because there are
not very many electrons
...
• Dispersion forces are present in all molecules
...
16
Dipole Forces
• Polar molecules have a permanent dipole
...
• The strength of a dipole force is typically 10% of a
covalent bond’s strength
...
than
• uneven electrons= dipole
Br
H
molecule
Br
H
molecule
17
Hydrogen Bonds
• Hydrogen bonds are a special type of dipole force
...
• Hydrogen bonds are especially important in water
and living organisms
...
Where do covalent bonds fit
into this ranking?
• 1
...
dipole forces
• 3
...
Permanent
dipoles are stronger
• since no O-H, N-H, or F-H bonds then dipole forces are the strongest
intermolecular attractions
• In a liquid with nonpolar molecules, what is the strongest type of intermolecular
attraction?
• Non polar molecules only have a dispersionforce (temporary dipole)
Intermolecular Forces Exercise
• Which types of intermolecular forces (dispersion force,
dipole force, or hydrogen bond) exists in each of the
following liquids?
a) C8H18 - only dispersion because it is non polar
b) CH3–OH- polar molecule ( O-H bond is polar)
• therefore liquid has dispersion, dipole and
hydrogen bond
c) CH3–O–CH2–CH3- polar molecule)C-O bond is polar) therefore liquid has
dispersion and dipole forces
what kinds of intermolecular forces are present in each
substance?
a) HCl - dispersion, dipole-dipole
b) H2O- hydrogen, dispersion, dipole-dipole
c) Br2- dispersion
d) He- dispersion
22
Physical Properties of Liquids
• There are 4 physical properties of liquids that we
can relate to the intermolecular attractions present
in the molecules:
1
...
Boiling Point
3
...
Surface tension
23
Vapor Pressure
• At the surface of a liquid, some molecules gain
enough energy to escape the intermolecular
attractions of neighboring molecules and enter the
vapor state
...
• The reverse process is condensation
...
24
Vapor Pressure Continued
• The stronger the intermolecular forces between the
molecules in the liquid, the less molecules escape
into the gas phase
...
25
Vapor Pressure Comparison
• Lets compare water and ether (from chart):
– Water has strong intermolecular attractions and ether
has only weak intermolecular attractions
...
pressure
• At 35°C, ether has a significant vapor
and water does not
...
Temperature
• As the temperature
increases, the vapor
pressure of a liquid
increases
...
Chapter 13
27
Boiling Point
• The normal boiling point of a substance is the
temperature where the vapor pressure is equal to
the standard atmospheric pressure
...
• A liquid with a high boiling point has a low vapor
pressure
...
• Viscosity is the result of an attraction between
molecules
...
29
Surface Tension
• The attraction between molecules at the surface of
a liquid is called surface tension
...
• The stronger the intermolecular attractions, the
stronger the surface tension of a liquid
...
which one is more polar?)
• isopropyl alcohol is polar……………
...
• Electronegativity difference of H- F bond is 4
...
1=1
...
8-2
...
7
• HF is more polar and has a stronger intermolecular bond
• HF will have a higher boiling point because it is polar and will
take longer to boil
34
Boiling Point
• Liquids that evaporate easily are termed volatile
...
• Which compound out of HF and HBr will be more
volatile? Why?
• HBr is more volatile because it has weaker
intermolecular dipole forces (its molecules
separate into a gas easier)
35
Based on what we just learned about
intermolecular forces, how is this
possible???
»
...
• We can study the solid state and make 5 general
observations
...
Solids have a fixed shape and volume
...
2
...
• Crystalline solids contain particles in a regular,
repeating pattern (ex salt), noncrystalline solids do not
(ex rocks)
...
Solids do not compress or expand to any degree
• Assuming no change in physical state, temperature
and pressure have a negligible effect on the volume of
a solid
...
Solids have a slightly higher density than their
corresponding liquid
• One important exception is water; ice is less dense
than liquid water
...
Solids do not mix by diffusion
• The particles are not free to diffuse in a solid
heterogeneous mixture
...
• In table salt, NaCl, sodium
ions and chloride ions are
arranged in a regular threedimensional structure referred
to as a crystal lattice
...
40
Molecular Solids
• A crystalline molecular
solid has molecules
arranged in a particular
conformation
...
• Other examples of crystalline molecular solids
are table sugar, C12H22O11, and sulfur, S8
...
of
• A metallic crystal is made up
positive metal ions
surrounded by
valance electrons
...
• Referred to as the “electron sea” model
...
• There is nothing in the whole
network that is considered an
individual molecule
...
Ionic Solids:
Held together by strong ionic bonds which are not broken easily resulting
in higher melting points
...
General Properties of Solids
Solids Exercise
• The following are solids at room temperature (25°C)
...
• These intermolecular attractions affect the physical
properties of substances
...
49