chapter 10 the liquid and solid states - bakersfield college notes/chapter 10... ·...
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Chapter 10The Liquid and Solid States
• Changes of State
• Intermolecular Forces
• Properties of Liquids
• Properties of Solids
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Particles are widely
separated with much
free space
Some free space between particles
Little free space between particles
Compressed under moderate pressure
Can be compressed
slightly by moderate pressure
Little or no volume
change under moderate pressure
Particles move through space
Particles move past one another
Particles fixed in place
but vibrate around a fixed position
Fills containerCan be pouredShape remains rigid
Takes shape of container
Takes shape of filled portion of container
Shape not set by container
No fixed shapeNo fixed shapeFixed shape
GasLiquidSolid
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Solids, Liquids, and Gases
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Figure 10.4
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Changes of State• Transitions between these states
• Also called phase changes
• 6 main phase changes:
– Evaporation (also called vaporization)
– Condensation
– Freezing
– Melting (also called fusion)
– Sublimation
– Deposition 10-
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Liquid-Gas Phase Changes
• Evaporation (vaporization)– At the surface of a
liquid, some molecules may have sufficient kinetic energy to escape into the gas state.
– Heat is required to maintain the temperature needed for evaporation.• Evaporation is an
endothermic process.
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Liquid-Gas Phase Changes
• Condensation– Transition from a gas to a liquid
– Occurs when gas particles cannot escape the container and thus, come into contact with a liquid
– An exothermic process (energy is released)
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Figure 10.9 (cropped for only the top portion)
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Equilibrium• A state in which opposing processes occur at
equal rates• An equilibrium is designated by a double arrow,
such as:
liquid gas
• In the above equilibrium, the rates of evaporation and condensation are equal.
• The gas produced by evaporation exerts a pressure on the liquid below it.– At equilibrium, this pressure is called vapor
pressure.• Vapor pressure increases as temperature
increases.10-
vaporization
condensation
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Boiling Point• The temperature at
which boiling occurs
– Boiling occurs when
the vapor pressure equals the external pressure of the
atmosphere
• Normal boiling point
– Occurs when the atmospheric pressure is exactly 1 atm
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Practice – Vapor Pressure Curves
• Consider the vapor pressure curve for propane to the left, which is used as a fuel in barbeque grills.
What is the normal boiling point for propane? What is its boiling point at 0.40 atm?
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Practice Solutions – Vapor Pressure Curves
• What is the normal boiling point for propane?
The normal boiling point is found at a pressure of 1.0 atm. At this pressure, the boiling is about -41°C.
• What is its boiling point at 0.40 atm?
At 0.40 atm, the boiling point is about -60°C.
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Liquid-Solid Phase Changes• Freezing
– The average kinetic energy of a liquid molecules fall when it is cooled
– If the KEav falls low enough, then the molecules become fixed in position into the solid
– Therefore, freezing is the conversion of a
liquid into a solid
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Liquid-Solid Phase Changes• Freezing point
– The temperature at which the freezing of a liquid into a solid state occurs
• As with boiling temperature, the two states are in equilibrium with one another.
solid liquid
– Normal freezing point
• The temperature when the freezing equilibrium is achieved under a pressure of 1 atm.
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melting
freezing
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Freezing
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Figure 10.11
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Melting• Melting
– Phase change from solid to liquid
– Reverse of freezing
– Opposite process of freezing
– Also called fusion
• Melting point– Same temperature
as freezing point
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Figure 10.12
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Solid-Gas Phase Changes• Sublimation
– Evaporation of a solid
– Occurs when a solid has a high vapor pressure
– Solid can change directly from a solid to a gaseous state without going through the liquid state
• Deposition– Can go directly from gas
to solid without passing through the liquid state
– Reverse of sublimation
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Practice – Changes in the State of Matter
• Identify the process shown in the
following diagram:
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Diagram from Practice Problem 10.2
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Practice Solutions – Changes in the State of Matter
• In the starting material, there is a large distance between particles, so we can identify it as a gas. In the ending material, the particles are closely spaced and not random, and thus it is a solid. The gas to solid transition is called deposition.
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Cooling Curve• Shows the phase changes of a substance in a
graph plotting temperature versus heat
removed at constant pressure
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Heating Curve• Shows the phase changes of a substance in a
graph plotting temperature versus heat added
at constant pressure
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Practice – Cooling and Heating Curves
• The diagram to the top right represents the physical states of a substance.
Identify where each state would predominate on the heating curve given to the right.
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Practice Solutions – Cooling and Heating Curves
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Energy Changes• Each change of state takes place at
constant temperature• Any phase change is accompanied by an
energy change– The change in energy for each process is
called the heat of that process (q)
q = mC∆T– Molar heat of fusion
• Energy required to melt 1 mole of a substance
– Molar heat of vaporization• Energy required to evaporate 1 mole of a
substance10-
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Practice – Energy for Phase
Changes• Calculate the heat required to boil
125 g of water at 100.0°C. The molar
heat of vaporization of water is
4.07 x 104 J/mol.
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Practice Solutions – Energy for
Phase ChangesBecause the heat of vaporization is in J/mol,
and since J is the unit for heat, we only need to cancel out moles. To do this, we need to
convert grams of water into moles of water using water’s molar mass, then multiply by the heat of vaporization to find Joules:
125 g H2O x 1 mol H2O x 4.07 x 104 J
18.01 g H2O 1 mol H2O
= 2.82 x 105 J
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Intermolecular Forces• An attractive force that operates between
molecules
• There are many kinds of intermolecular forces:
– London dispersion force
– Dipole-dipole force
– Hydrogen-bonding force
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Polar molecules
containing unpaired
molecules and a hydrogen bonded to
nitrogen, oxygen, or
fluorine
Two dipoles, one containing hydrogen to
an electronegative
element and the other containing an
electronegative element,
attract one another.
Hydrogen-Bonding Force
Polar moleculesPolar molecules
(permanent dipoles)
attract one another
Dipole-Dipole Force
All atoms and molecules
A temporary dipole in one molecule induces
the formation of a
temporary dipole in a nearby molecule and is
attracted to it.
London dispersion
force
OccurrenceType of
Interaction
Type of
Force
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London Dispersion Forces• Instantaneous dipole
– A temporary dipole formed when the electrons in an atom or nonpolar molecule happen to be more on one side in an instant in time,
causing it to be more negative than normal and the opposite side positive
• Induced dipole
– Positive end of the dipole exerts an attractive force on nearby electrons, causing an adjacent atom to develop into another
temporary dipole
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London Dispersion Forces• London dispersion force
– The attraction between temporary dipoles
– Occurs between atoms and molecules
– Only intermolecular force in nonpolar substances
– Tend to be stronger the larger the atom or molecule
– Relatively weak forces
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Practice – London Dispersion
Forces• Which has stronger London
dispersion forces, CH4 or SiH4?
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Practice – London Dispersion
Forces• Which has stronger London
dispersion forces, CH4 or SiH4?
Since silicon is larger than carbon,
SiH4 interactions are stronger than
CH4 interactions. The larger the
electron cloud, the easier it is to
distort it, resulting in larger London
dispersion forces.
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Dipole-Dipole Forces
• Attraction between polar molecules
• Occurs when the partially positive end of one molecule attracts the partially negative end of another molecule
• Generally stronger than London dispersion forces
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Practice – Dipole-Dipole Forces
• Which of the following molecules
experience dipole-dipole forces?
a) SCl2b) CO
c) NH3
d) CCl4
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Practice Solutions –
Dipole-Dipole Forces
• Which of the following molecules experience dipole-dipole forces?a) SCl2
SCl2 has a bent structure similar to water’s structure, and therefore, an overall molecular dipole towards the lone pairs on S. This molecule experiences dipole-dipole forces.
b) COCO has a linear structure with one lone pair on the C and O. Since O is more electronegative than C, this molecule has a molecular dipole towards the O. This molecule experiences dipole-dipole forces.
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Practice Solutions –
Dipole-Dipole Forces• Which of the following molecules
experience dipole-dipole forces?c) NH3
NH3 has a trigonal pyramidal structure, and therefore, an overall molecular dipole towards the lone pair on N. This molecule experiences dipole-dipole forces.
d) CCl4CCl4 has a tetrahedral structure. Since all the atoms around central atom are the same, CCl4 is a nonpolar molecule. This molecule does NOT experience dipole-dipole forces.
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Boiling Points
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Hydrogen Bonding• Special type of dipole-
dipole force
• Only occurs in molecules that contain hydrogen bonded to a small, highly electronegative element
• Stronger than a regular dipole-dipole force
• Important force in living systems by stabilizing
molecular shapes
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Hydrogen Bonding
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Figure 10.21
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Practice – Hydrogen Bonding
• Identify the molecules from the
following list that experience
hydrogen bonding in the pure liquid
state: N(CH3)3, CH3CO2H, and HOCl.
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Practice Solutions – Hydrogen Bonding
• Identify the molecules from the following list that experience hydrogen bonding in
the pure liquid state: N(CH3)3, CH3CO2H, and HOCl.
CH3CO2H and HOCl experience hydrogen bonding because the hydrogen atoms in
these molecules are bonded to oxygen, a small, highly electronegative element.
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Practice Solutions – Hydrogen Bonding
• Identify the molecules from the following list that experience hydrogen bonding in the pure liquid state: N(CH3)3, CH3CO2H, and HOCl.
In N(CH3)3 the hydrogen atoms are bonded to carbon, which has a relatively similar electronegativity. Therefore, N(CH3)3 does not experience hydrogen bonding.
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Trends in Intermolecular Forces• Remember:
– London forces exist between all atoms and molecules.
– Dipole-dipole moments exist in only polar compounds.
– Hydrogen bonds only exist in polar compounds that contain hydrogen.
• In terms of strength (magnitude), intermolecular forces compare as shown below:
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Figure 10.23
Molecules
experiencing
London dispersion forces
only
Molecules also
experiencing dipole-dipole
forces
Molecules also
experiencing hydrogen
bonding
< <
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Practice – Trends in Intermolecular Forces
• Consider the substance CO and HF.
Which has the stronger
intermolecular forces? Which has
the higher melting point? Boiling
point? Vapor pressure?
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Practice Solutions – Trends in Intermolecular Forces
• Consider the substance CO and HF. Which has the stronger intermolecular forces? Which has the higher melting point? Boiling point?
Vapor pressure?
HF has the stronger intermolecular forces because it has hydrogen bonding, whereas CO
only experiences dipole-dipole forces. Higher temperatures are required to overcome the stronger forces in HF, therefore it will have the
higher melting and boiling points. 10-
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Practice Solutions – Trends in Intermolecular Forces
• Consider the substance CO and HF. Which has the stronger intermolecular forces? Which has the higher melting point?
Boiling point? Vapor pressure?
Because of the lower energy required for evaporation, at any temperature CO will
have a higher vapor pressure than HF.
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Properties of Liquids• Are related to the distance
between particles and to intermolecular forces
• Particles in a liquid are much closer together than the particles in a gas
• Liquid particles are not fixed, as they are in a solid
• Three common properties of liquids: – Density– Viscosity– Surface tension
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Density• Remember:
• Densities of the states of matter are related to the distance between particles
• Most substances are denser as solids
than as liquids because their molecules or atoms are closer together
– Water is an exception in that ice is less dense than liquid water
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volume
mass d =
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Viscosity• Liquids and gases are fluids.
– A fluid is any substance that can flow
• Viscosity is the resistance of a
substance to flow.
– Generally, the viscosity of liquids is low
• Viscosities generally vary by
increasing with the magnitude of
their intermolecular forces and with
molecular size.10-
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Surface Tension• The amount of work
required to increase the surface area of a liquid by a unit amount
• Causes a liquid surface to behave like a stretched membrane
• The greater the intermolecular forces in a liquid, the greater the surface tension
• Surface tension decreases as temperature increases
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Figure 10.27
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Meniscus• Either a concave or convex curved surface of a liquid
produced by intermolecular forces• A concave surface occurs when the intermolecular
forces between the liquid and the glass are greater than the intermolecular forces among the liquid molecules
• A convex surface occurs when the intermolecular forces between the liquid and the glass are less than the intermolecular forces among the liquid molecules
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Amorphous and Crystalline Solids• Amorphous solid
– Occurs when the temperature of a liquid drops rapidly, resulting in the particles solidifying in a partially disordered state
– Particles are somewhat randomly arranged– Lacks regular form
• Crystalline solid– Occurs when a liquid solidifies slowly,
allowing the array of particles to become well ordered
– Most solids are of this type– Results in the symmetrical arrangement of
planar faces
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Amorphous and Crystalline Solids
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Figure 10.31
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Crystals and Crystal Lattices• Crystal
– An orderly, repeating, three-dimensional assembly of fundamental particles (atoms,
molecules, or ions)
• Crystal lattice
– Pattern forms by repeating arrays of crystal
– Also called crystal structure
– Atoms, molecules, or ions are arranged in close-packed structures
• Orderly arrangement that is an efficient way to use space
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Other Close-Packed Arrangements
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Types of Crystalline Solids• Solids show a wide range of properties such
as:– Melting point
– Hardness
– Malleability
• The types of forces holding the fundamental particles together help explain the properties
• 4 Types of crystalline solids– Metallic solids
– Ionic solids
– Molecular solids
– Network solids
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Low melting point; soft; poor heat conductors; electrical
insulators
London dispersion
forces
Nonpolar
molecules
Very high melting point; very hard; somewhat brittle; non- or
semiconductors
Covalent
bondsAtomsNetwork
Low to moderate melting point; variable hardness; may
be brittle; nonconductors
Dipole-dipole
forces
Polar
molecules
Molecular
High melting point; hard,
brittle; nonconductors when
solid; electrical conductors when melted
Ionic bondsCations and
anionsIonic
Low melting point & soft; or high melting point & hard;
good heat & electrical conductors; malleable &
ductile
Attractions
between nuclei and delocalized
electrons
AtomsMetallic
Fundamental
Particles
Attractive
ForcesProperties
Type of
Solid
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Practice – Types of Crystalline Solids
• A crystalline solid is very hard, does
not conduct electricity when solid or
when melted, and has a high melting
point. What type of solid is it?
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Practice Solutions – Types of Crystalline Solids
• A crystalline solid is very hard, does not conduct electricity when solid or when
melted, and has a high melting point. What type of solid is it?
This solid is a network solid. Network
solids are the only crystalline solids that have high melting points, are very hard,
and have the possibility of
nonconductors.
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Metallic Solids• Valence electrons
move freely through all parts of a metal
• Attractions between atoms of a metal are delocalized, and therefore it is easy to move atoms by applying force
• Ductile and malleable
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Alloys• Forms when a metal is mixed with one or
more additional metallic or nonmetallic elements
• Have properties different than those of their parent elements
• Table 10.4
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Ionic Solids• Contain cations and
anions arranged in crystalline solids
• Electrostatic forces (ionic bonds) hold together ionic crystals
• High melting points• Hard and brittle• Solids are not electrical
conductors, but melted or dissolved, they become good conductors
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Superconductors• Offer no resistance to the conduction of electrical
current
• Repel magnetic fields
• Although the nature of superconductors is not entirely understood, the crystal structure of the solid material does play a role
• Often formed from silicon and/or other metalloids
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Molecular Solids• Intermolecular forces between molecules hold
a molecular solid together
– Nonpolar solids are held together by London dispersion forces
• Form soft crystals with low melting points
• Electrical insulators
• Poor conductors of heat
– Polar solids are held together by London dispersion forces and dipole-dipole forces
• Typically harder than nonpolar solids
• Low to moderate melting points
• Electrical insulators (no ions)
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Molecular Solids
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Network Solids• Consists of a giant
molecule that forms the entire crystal
• Formed by metalloids or carbon
• Strong covalent bonds connect the atoms in a network solid
• Poor electrical conductors• High melting points• Very hard• Have very stable, three–
dimensional structures• Many have a diamond
structure, or some derivative of it
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Network Solids
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Practice – Structures of Solids• Identify the type of solid shown by
the following molecular-level image.
What types of forces hold the
particles together in this solid?
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Practice Solutions – Structures of Solids
• This diagram shows a molecular solid.
Since it is made of nitrogen atoms exclusively, it is nonpolar and is therefore
held together by weak London forces.