Transcript Chapter 11- Intermolecular forces, liquids, and solids

Intermolecular Forces, Liquids,
and Solids
Chapter 11/12
Intermolecular Forces vs.
Intramolecular Forces
Intermolecular Forces
• The stronger the attractive
forces in a liquid, the higher
the temperature at which the
liquid boils
Intermolecular Forces
• The stronger the attractive
forces in a solid, the higher
the temperature at which the
solid melts
Three Types of Intermolecular
Forces
• Dipole-Dipole Force,
London Dispersion forces,
and hydrogen bonding forces
• A fourth force is an IonDipole Force
Forces
• All four forces are
electrostatic and tend to be
less than 15% as strong as an
ionic or covalent bond
Ion-Dipole Forces
• exist between the ion and the
partial charge on the end of a
polar molecule
• important in solutions
Dipole-Dipole Forces
• Neutral polar molecules
attract to each other when the
positive end of one molecule
is near the negative end of
another
Dipole-Dipole Forces
• effective when polar
molecules are close to one
another
• weaker than ion-dipole
forces
Dipole-Dipole Forces
• For molecules of equal mass
and size, the strengths of
intermolecular attractions
increase with increasing
polarity
London Dispersion Forces
• the motion of electrons in an
atom or molecule can create
an instantaneous dipole
moment
London Dispersion Forces
• In one second, when the
electrons are on the same
side of an atom, it can
influence its neighbor
causing an attraction between
the two
London Dispersion Forces
• The ease at which the charge
distribution in a molecule can
be distorted is called
polarizability
London Dispersion Forces
• The more polarizability in a
molecule, the stronger the
London dispersion forces
London Dispersion Forces
• increase in strength with
increasing molecular weight
and depend on shape
• exist between all molecules,
polar and nonpolar
Sample Exercise 11.1 Comparing Intermolecular Forces
The dipole moments of acetonitrile, CH3CN, and
methyl iodide, CH3I, are 3.9 D and 1.62 D,
respectively.
(a)Which of these substances has greater dipole–
dipole attractions among its molecules?
(b)Which of these substances has greater London
dispersion attractions?
(c)The boiling points of CH3CN and CH3I are
354.8 K and 315.6 K, respectively. Which
substance has the greater overall attractive
forces?
Sample Exercise 11.1 Comparing Intermolecular Forces
Of Br2, Ne, HCl, HBr, and N2, which is likely to
have
(a) the largest intermolecular dispersion forces,
(b) the largest dipole–dipole attractive forces?
Hydrogen Bonding
• intermolecular attraction
between the H atom in a polar
bond(H-F, H-O, or H-N) and an
unshared electron pair on a
nearby electronegative ion or
atom(usually N,F, or O)
Hydrogen Bonding
• Considered a unique dipoledipole interaction due to the
electronegativity of N,F, and O
• Stronger than dipole-dipole or
dispersion forces
Hydrogen Bonding
Identify the attractive forces
between the following:
Sample Exercise 11.2
Identifying Substances that Can Form
Hydrogen Bonds
In which of the following substances is
hydrogen bonding likely to play an
important role in determining physical
properties: CH4, H2NNH2, CH3F,
H2S,CH2Cl2, H2O2, CH3COCH3, PH3 ?
Comparing Intermolecular Forces
Sample Exercise 11.3
Predicting the Types and Relative Strengths of
Intermolecular Attractions
• List the substances H2, CO, HF, and Ne in
order of increasing boiling points.
• Identify IMF’s present in the following
substances and order their bp: CH3CH3,
CH3OH, and CH3CH2OH.
Properties of Liquids
• Viscosity is the resistance of
a liquid to flow
• depends on the
intermolecular forces
Viscosity
Properties of Liquids
• Surface tension is the energy
required to increase the surface
area of a liquid by a unit
amount.
• A force is pulling molecules
from the surface inward.
Surface tension
Phase Changes
Phase Changes
• accompanied by a change in
energy of the system
Heating Curves
• Graph of the temperature of
the system versus the amount
of heat added.
Phase Diagrams
• graphical way to summarize
the conditions under which
equilibrium exists between
different states of matter
General Phase Diagram
• Includes three important
curves which represent
temperatures and pressures
where the various phases can
co-exist
General Phase Diagram
• The line from A to B is the
vapor pressure curve.
• It represents the equilibrium
between the liquid and gas
phase.
• The normal bp is found at 1 atm
on this curve
Critical Point
• Point B is where the critical P
and T are found
• Beyond the critical point the
liquid and gas phase are
indistinguishable
General Phase Diagram
• Line AC represents the
equilibrium between solid
and gas
General Phase Diagram
• The line AD represents the
equilibrium between the solid
and liquid phase
• The mp and fp are identical, and
differ only in direction
• The normal mp is at 1 atm
General Phase Diagram
• Point A is the Triple Point,
where the three phases
intersect and are at
equilibrium
Phase Diagram of Water
• the mp of water decreases
with increasing pressure
because the liquid form is
more compact than the solid
form
Phase Diagram of CO2
• There is no normal mp in
CO2.
• At 1 atm pressure, the
substance will sublime
Sample Exercise 11.6 Interpreting a Phase diagram
Describe any changes in the phases present when H2O is
(a) kept at 0 °C while the pressure is increased from that at point 1
to that at point 5
(b) kept at 1.00 atm while the temperature is increased from
that at point 6 to that at point 9
Structures of Solids
• Crystalline Solids
– Atoms, ions, or molecules are ordered in a
well-defined three-dimensional arrangements;
they have flat surfaces or faces and regular
shapes
– Quartz and diamond are crystalline solids
Structures of Solids
• Amorphous Solids
– Solids in which particles have no orderly
structure; lack faces and shape
– Rubber and glass are amorphous solids
Structures of Solids
Bonding in Solids - Molecular Solids
• Atoms or molecules (nonmetals) held
together by IMF’s
• Soft, low mp, poor conductors
Bonding in Solids – Covalent-Network Solids
• Atoms held together in large networks or
chains by covalent bonds
• Hard, high mp, variable conductors
Bonding in Solids - Ionic Solids
• Ions held together by ionic bonds
(electrostatic forces)
• Hard, brittle, high mp, poor conductors
Bonding in Solids - Metallic Solids
• Metal atoms
• Visualize the metals as an array of positive
ions immersed in a sea of delocalized
valence electrons
• soft to very hard, low to high mp, excellent
conductors, malleable and ductile
Alloys
• Mixture of elements exhibiting metallic
properties
Summary of Bonding in Solids