Chapter 11 Flashcards
The vapor pressure of a liquid at a particular temperature is the
the partial pressure of the vapor over the liquid measured at equilibrium.
The vapor pressure depends on the
liquid and on the temperature.
boiling point
the temperature at which the vapor pressure is equal to the pressure on the liquid, usually atmospheric pressure. At this temperature, bubbles of gas form within the liquid.
The normal boiling point is measured at
1-atmosphere pressure.
When the pressure on the liquid increases, as is the case with a pressure cooker, the boiling point
increases
when the pressure on the liquid decreases, as is the case at high altitude, the boiling point
decreases
freezing point
the temperature at which a pure liquid changes to a crystalline solid (or freezes)
melting point
the temperature at which a crystalline solid changes to a liquid (or melts).
heat of fusion
the heat needed to melt a solid. It is given in kJ/mol
heat of vaporization
the heat needed to vaporize a liquid. It is given in kJ/mol
The Clausius–Clapeyron equation
can be used to find the vapor pressure, the heat of vaporization, or the temperature.
phase diagram
graphical way to summarize the conditions under which the various states of a substance are stable. •In a phase diagram, phases are separated by lines that represent equilibrium between those phases
triple point
the point where all three phases are in equilibrium.
critical point
gives the temperature (critical temperature, TC) at which the liquid state can no longer exist and the pressure at that temperature (critical pressure). Above this temperature and pressure, there is only one state, a supercritical fluid.
Surface tension
the energy required to increase the surface area of a liquid by a unit amount. The values are given in J/m2.
Surface tension arises because
the molecules at the surface of a liquid experience a net force toward the center of the liquid.
is the property that allows insects to walk on the surface of water or a pin to float
surface tension
viscosity
is the resistance to flow exhibited by liquids and gases
the 3 types of intermolecular forces
Dipole-Dipole forces, London forces, Hydrogen bonding forces
van der waals forces
a general term that includes both dipole-dipole forces and London forces.
- no dipole-dipole force in nonpolar molecules
- but there is still a force of attraction
- Fritz London explained this relationship and is now call the London forces
polar molecules exhibit
dipole-dipole forces that result in alignment of the molecules
London (dispersion) forces (LDF) in a non polar molecule
the charge is uniformly distributed over time. But in any one instant, the charge is not uniformly distributed. In that instant, there is an instantaneous dipole. To see how this works, let’s look at a neon atom
The instantaneous dipole of the neon atom induces an
instantaneous dipole in adjacent atoms, resulting in an attractive force between them.
how do instantaneous dipoles usually change
However, the instantaneous dipoles tend to change together,maintaining the attractive force between them.
London (dispersion) forces (LDF)
- London forces are the weak attractive forces between molecules resulting from the small, instantaneous dipoles that occur because of the varying positions of the electrons during their motion about the nuclei.
- All molecules exhibit London forces.
london forces increase with
increasing mass (atomic number) because the presence of more electrons causes a stronger instantaneous dipole.
the more polarized the LDF . . .
the more easily distorted the molecules will be
______ compounds have the strongest intermolecular forces and the highest heat of vaporization because it is most flexible and, therefore, most polarizable.
straight-chain compounds
The most _____ compound has the weakest intermolecular forces and the lowest heat of vaporization
compact
The stronger the intermolecular forces, the
higher the heat of vap
the lower the vapor pressure at any given temperature, the
higher the surface tension and the more viscous the liquid is
Each molecule has one or more
-OH group
Molecules with this group (-OH) have an additional force called the
hydrogen bonding force
Hydrogen bonding
is a weak attractive force that exists between hydrogen atoms bonded to a very electronegative atom, X, and a lone pair of electrons on another small, electronegative atom, Y.
Most often, X is __, ___, or ___, the smallest, most electronegative elements.
F, O, or N,
A solid is a nearly incompressible state of matter with a well-defined shape, because
the units (atoms, molecules, ions) making up the solid are in close contact and reside in fixed positions or sites.
molecular solid
consists of atoms or molecules. It is held together by intermolecular forces.
metallic solid
consists of the positive cores of metal atoms. It is held together by metallic bonding, a “sea” of delocalized electrons.
ionic solid
composed of cations and anions. It is held together by ionic bonds, the electrical attractions between oppositely charged particles
covalent network solid
consists of atoms. These atoms are held together in large chains or networks by covalent bonds.
Carbon exists as a _______ solid in both the graphite and diamond forms
covalent network
In general, molecular solids have _____
lower melting points
covalent network solids and ionic solids have ___________
high melting points
The melting points of ionic solids vary owing to differences in
lattice energy that reflect the charge and sizes of the ions involved.
The melting points of metals
vary widely
Hardness depends on
how easily the structural units can be moved relative to one another.
Molecular solids tend to be
soft
Covalent network solids, such as diamond, are
very hard
Ionic compounds are _____ because they tend to fracture easily along crystal planes.
brittle
Metals are ______ so that they can be easily shaped by hammering
malleable
Metals are good electrical conductors because of
their delocalized valence electrons.
Ionic solids do not______. When melted, however, they ____. They also conduct electricity when ________
conduct electricity; do conduct electricity: they are dissolved in water.
crystalline solid
composed of one or more crystals with a well-defined ordered structure in three dimensions
amorphous solid (and an example)
has a disordered structure and lacks a well-defined arrangement of basic units.
Glass is an amorphous solid obtained by cooling a liquid rapidly enough that its basic units are “frozen” in random positions before they can assume a crystalline arrangement
crystal lattice
is the geometric arrangement of lattice points of a crystal in which we choose one lattice point at the same location within each of the basic units of the crystal
cubic crystal (3 possible unit cells)
There are three possible unit cells: simple cubic, body-centered cubic, and face-centered cubic.
simple cubic (Coordination Number and Number of Atoms Per Unit Cell)
CN=6
atom/unit cell(8 x 1/8 = 1)
body-centered cubic (Coordination Number and Number of Atoms Per Unit Cell)
CN=8
2 atoms/unit cell(8 x 1/8 + 1 = 2)
face-centered cubic (Coordination Number and Number of Atoms Per Unit Cell)
CN=12
atoms/unit cell(8 x 1/8 + 6 x 1/2 = 4)
