Chapter 11: Liquids & Solids The molecular compounds like
water, ammonia, and carbon dioxide have different physical
properties because of the intermolecular forces. Comparison of all
three phases: Slide 2 Liquids & Solids Slide 3 Slide 4
Compressibility Slide 5 Changes of State Changes in state can be
induced by a change in temperature or pressure. Slide 6
Intermolecular Forces Forces between molecules. Always LESS in
energy than actual bond. The attractive force between two HCl
molecules is about 16 kJ/mol. The bond dissociation energy of the
HCl bond is about 431 kJ/mol. Slide 7 Intermolecular Forces One
method to compare the strength of intermolecular forces is to
examine the substances boiling point. When the forces are
relatively weak, then the boiling point is small. Ex) HCl, bp = -85
o C. There are three main types of intermolecular forces between
neutral substances. Slide 8 Intermolecular Forces In the LS packet,
we identified molecules as being polar or non-polar based on shape,
types of atoms, etc. Polar molecules have a dipole that is a
positive and negative end. Slide 9 Intermolecular Forces Thus, the
first type of force is called Dipole-Dipole (or DD) forces and
occurs for any polar molecule. The larger the dipole moment, the
more DD forces. Slide 10 Intermolecular Forces If you cool any
non-polar molecule or atom to a low enough temperature, then it
will liquefy. Yet, these have no reason to be attractive to each
other. Fritz London first proposed a theory in 1930. On average,
electrons in an atom like He are evenly distributed. But, in one
INSTANT, the two electrons may both be on the same side. Slide 11
Intermolecular Forces Thus, in that one INSTANT, a He atom would
have an instantaneous dipole. This is called the London Dispersion
(or LD) force. Slide 12 Intermolecular Forces Since all molecules
have electrons, they all have a LD force. The polarizability of an
atom or molecules electrons depends on two factors. 1. The number
of electrons. More electrons = More LD forces. 2. The shape of
molecule. More spread out = more LD forces. Slide 13 Intermolecular
Forces Slide 14 Non-polar Alkanes Slide 15 Intermolecular Forces
The formula C 5 H 12 has three structural isomers. CH 3 CH 2 CH 2
CH 2 CH 3 CH 3 CH 3 CH 3 CH 2 CH CH 3 CH 3 C CH 3 CH 3 Slide 16
Non-polar Branched Alkanes NameMolar MassBoiling Point Pentane72.15
g/mol36.1 o C Methylbutane72.15 g/mol27.7 o C Dimethylpropane72.15
g/mol10 o c Butane58.12 g/mol-0.5 o C Methylpropane58.12 g/mol-11.7
o C Slide 17 Comparison of the group 4A, 5A, 6A, and 7A hydrides
shows an interesting result. What type of forces do the group 4A
have? Group 6A? What is the notable exception? Slide 18
Intermolecular Forces The third type of force is a special case of
DD force and is called Hydrogen Bonding (or HB). The name Hydrogen
Bonding is a misnomer! HB can only occur when: H is bonded to
either N, O, or F. The N, O, or F atom has at least one lone pair.
Slide 19 Intermolecular Forces The strength of Hydrogen Bonding
varies from 5 kJ to 40 kJ, which is still much weaker than a
covalent bond (200 1000 kJ). However, it is MUCH stronger than DD
or LD forces. Thus, it can greatly increase the boiling point
temperatures of molecules. Slide 20 Intermolecular Forces HB forces
are very important in biochemistry. Proteins are made from the
twenty amino acids. The structure of the amino acid has both an OH
group and an NH 2 group that can HB. R O H N C C O H H H Slide 21
Intermolecular Forces Predicting relative boiling points. 1.
Determine the molecular weight. 2. Determine the type(s) of
intermolecular forces present. If weights are similar, then LD <
DD < HB If weights are very dissimilar, then #2 probably does
not matter. However, HB can really distort the bps! Ex) H 2 O, bp =
100 o C, MW = 18 g/mol versus CCl 4, bp = 76 o C, MW = 154 g/mol.
Slide 22 Intermolecular Forces The strengths of attractions between
the molecules may affect a liquids properties. Viscosity Surface
Tension Slide 23 Intermolecular Forces Viscosity is the resistance
of a liquid to flow. Liquids with low viscosity, like water, will
produce a splash whereas liquids with high viscosity, like corn
syrup or ketchup, will not. Slide 24 Intermolecular Forces
Viscosity tends to increase with more intermolecular forces and
molecular weight. Many liquids, like water, have a consistent
viscosity over a wide range of temperatures. Some liquids, like
corn syrup, will decrease in viscosity as the temperature
increases. Multi-weight motor oil actually increases with an
increase in temperature (ie. 5W 30). Non-Newtonian liquids (ie.
Slime) have a variable viscosity at the same temperature. Slide 25
Surface Tension Surface Tension is the skin-like appearance of the
surface. Results from surface molecules seeking six nearest
neighbors like interior molecules. Slide 26 Surface Tension Slide
27 Phase Changes Slide 28 Energy when changing between solid and
liquid phase is called the Heat of Fusion and denoted as H fus. H
fus for water is 6.01 kJ/mol or 334 J/g. Energy when changing
between liquid and gas is called the Heat of Vaporization and
denoted as H vap. H vap for water is 40.67 kJ.mol or 2,260 J/g.
Slide 29 Heating Curve Slide 30 Refrigeration The basics of
refrigeration. First law of thermodynamics at work again! Coolant
is CF 2 Cl 2 (old) or CF 3 CH 2 F (new). Slide 31 Vapor Pressure
Above the surface of any liquid, some liquid molecules will have
enough energy to escape and become gas molecules. In a closed
system, an equilibrium will be achieved between the gas molecules
and the liquid. This is the vapor pressure. Slide 32 Vapor Pressure
As the temperature of the liquid increases, its vapor pressure will
increase. Slide 33 Vapor Pressure When the vapor pressure equals 1
atmosphere, then the liquid spontaneously becomes a gas. You would
call this the boiling point. Does pure water always boil at 100 o
C? Slide 34 Clausius-Clapeyron Equation The graphs of vapor
pressure versus temperature are approximately an exponential
function. Mathematically, if you take the natural logarithm (ln key
on calculator) of the vapor press versus 1/T, then you get a linear
relationship. Slide 35 Clausius-Clapeyron Equation R is molar gas
constant = 8.314 J/K mol and the T is the temperature in Kelvin
Heat of vaporization must be in J/mol. Pressures can be in either
atm or mmHg (must agree). Slide 36 Phase Diagrams Display a singles
substances states of matter over a wide range of P and T. Slide 37
Carbon Dioxide The phase diagram of CO2 shows that the liquid phase
can only be found above a pressure of 5.11 atm. As the temperature
of solid CO2 increases, it undergoes sublimation. Slide 38 Water
The phase diagram of water has one very important difference. What
is it? Slide 39 Solids Solids can be either amorphous (random) or
crystalline (repeating pattern). Unit cell is the smallest
repeating pattern for the crystalline structure. Analogy: a hotel
with many floors. Structure of unit cell can have various lengths
and angles. Slide 40 Solids While many types of unit cells are
possible, a few are seen many times in structures of metals,
molecular, and ionic compounds. Cubic unit cells two main versions.
Body-centered cubic (BCC) has atoms at each corner and an atom in
the body-center. Face-centered cubic (FCC) has atoms at each corner
and an atom on each face. Important just like a hotel room shares
walls, floors, and ceilings with other rooms, so does a unit cell
share atoms with other unit cells. Slide 41 Solids Slide 42 Slide
43 Can also have atoms on edges in larger unit cells namely for
ionic compounds. Thus, the following are the contributions for
locations on or in a unit cell: Slide 44 Solids Unit cell
calculations will follow the formula: Where V c is the volume of
the cubic unit cell, MW is the molar mass, C is the number of atoms
per unit cell, D is the density (m/V), and N a is Avogadros Number.
Slide 45 Solids Another view Closest Packing Model. Assumes that
atoms are hard spheres. Maximize the density, minimize the empty
spaces. Slide 46 Solids First layer what is the most efficient
method of arrangement? Slide 47 Solids Second layer is placed so
that spheres sit in gaps from previous row. Third layer can either
repeat first layer yielding an ABABAB pattern. OR, the third layer
is offset from the first two producing an ABCABCABC pattern. Slide
48 Solids The ABABAB pattern produces a unit cell called hexagonal
closest packing or HCP. This is NOT a cubic unit cell! Slide 49
Solids The ABCABCABC pattern produces a unit cell called cubic
closest packing or CCP. However, CCP is the same as FCC! Slide 50
Solids HHe Hcp Li Bcc Be Hcp BCNOFNe Fcc Na Bcc Mg Hcp Al Fcc
SiPSClAr Fcc K Bcc Ca Fcc Sc Hcp Ti Hcp V Bcc Cr Bcc Mn Bcc Fe Bcc
Co Hcp Ni Fcc Cu Fcc Zn Hcp GaGeAsSeBrKr Fcc Rb Bcc Sr Fcc Y Hcp Zr
Hcp Nb Bcc Mo Bcc Tc Hcp Ru Hcp Rh Fcc Pd Fcc Ag Fcc Cd Hcp
InSnSbTeIXe Fcc Cs Bcc Ba Bcc Hf Hcp Ta Bcc W Bcc Re Hcp Os Hcp Ir
Fcc Pt Fcc Au Fcc HgTl Hcp Pb Fcc BiPoAtRn Slide 51 Solids All
crystalline solids can be catagerized into one of four types. Type
1: Molecular Solids Consist of atoms or molecules like Ne, CH 4,
and H 2 O. Are held together by relatively weak intermolecular
forces. Are soft and have low melting points (unless they have a
high MW). Poor conductors of heat and electricity. Slide 52 Solids
Type 2: Ionic Solids Consist of ions held together by their
electrostatic attractions. Unit cells are always larger since the
smallest repeating pattern must include two ions. When cation and
anion are of similar sizes, get BCC type arrangement. When anion is
much larger, get a CCP arrangement of anions with cations stuck in
the holes. Hard and brittle and have high melting points. Poor
electrical conductors as solids, but excellent when melted. Slide
53 Solids (a) CsCl (b) ZnS (c) CaF2 Slide 54 Solids View of NaCl
Slide 55 Solids Type 3: Metallic Solids Atoms are held together by
a sea of valence electrons. Can be soft (Na, Au) or very hard (Fe,
Co) with low to very high melting points. Excellent conductors of
both heat and electricity. Malleable and ductile. Slide 56 Solids
Type 4: Covalent Network Solids Consist of atoms held together in
large networks of covalent bonds. There are not many of these
C(diamond), SiO2, quartz, SiC, and BN. Very hard with very high
melting points. Poor conductors. Slide 57 Solids Two forms of
carbon, diamond and graphite. Slide 58 Solids Comparing metal
points of solids. First determine the type of solid. Molecular is
always the lowest of the four types. Second if both are the same
type of solid, then: Molecular is like bps. LD < DD < HB. Ex)
CH4 (-182 C) < COCl2 (-118 C) < H2O (0 C) Ionic depends on
lattice energy the larger the lattice energy, the higher the mp.
Ex) NaCl (801 C) < MgO (2852 C) Slide 59 Solids Metallic depends
on the number of unpaired electrons. More unpaired electrons =
higher melting point. K, 1 unpaired electron, mp = 64 C Ti, 2
unpaired electrons, mp = 1668 C Cr, 6 unpaired electrons, mp = 1907
C Cu, 1 unpaired electron, mp = 1065 C Covalent network are always
very high. Quartz, mp = 1670 to 1710 C Diamond, mp = 3550 C
(highest of any naturally occurring substance)
