intermolecular forces and liquids and solids · intermolecular forces has the higher boiling point...
TRANSCRIPT
1
Intermolecular Forces and Liquids and Solids
Intermolecular Forces and Liquids and Solids
Kinetic Molecular Theory of Liquids and Solids (12.1)Intermolecular Forces (12.2)Properties of Liquids (12.3)Crystal Structures (12.4)Bonding in Solids (12.5)Phase Changes (12.6)Phase Diagrams (12.7)
12.1 The Kinetic Molecular Theory of Liquids and Solids
How are solids and liquids modeled on the particle-level?How does this help explain macroscopic properties of solids and liquids?
Intermolecular Forces and Liquids and Solids
Figure 1.2, p. 4
H2O(l)
H2O(g)
H2O(s)
12.1 The Kinetic Molecular Theory of Liquids and Solids
Table 12.1, p. 403
12.1 The Kinetic Molecular Theory of Liquids and Solids
Does the molecular structure of the substance on the particle level affect function or properties on the macroscopic level?
We finally connect between the abstract (the bonding and structure of substances) to the observed (the function and properties of substances)
12.2 Intermolecular ForcesWhat are intramolecular forces:◦ Forces that hold atoms together in a molecule
What are intermolecular forces:◦ attractive forces between molecules
How do we model these?◦ Let’s consider water:
Intermolecular force (between molecules)
Intramolecular force (covalent bonds inmolecules)
12.2 Intermolecular Forces
Intermolecular force (between molecules)
Intermolecular vs Intramolecular
• 41 kJ to vaporize 1 mole of water (inter)
• 930 kJ to break all O‐H bonds in 1 mole of water (intra)
Generally, intermolecular forces are much weaker than intramolecular forces.
Intramolecular force (covalent bonds inmolecules)
12.2 Intermolecular Forces
Intermolecular force (between molecules)
“Measure” of intermolecular force:
boiling pointmelting pointΔHvap ΔHfus ΔHsub
Intramolecular force (covalent bonds inmolecules)
12.2 Intermolecular Forces
Focus on pure substances first:How do we model pure substances?How are intermolecular forces separated into categories?
We will use structure and size to assist in approximating intermolecular forces and connect this to physical properties
12.2 Intermolecular Forces
Can all substances be liquefied?Why?Dispersion Forces:◦ Attractive forces that arise as a result of a temporary
dipole induced in atoms or molecules
Figure 12.5, p. 406
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular ForcesPolarizability:◦ The ease with which the electron distribution in the atom
or molecule can be distorted
Polarizability increases with greater number of electrons or more diffuse electron cloud
Dispersion forces usually increase with molar mass.As dispersion forces increase, intermolecular forces increase.Therefore, it takes more energy to overcome these and the melting points and boiling points increase
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular Forces
Table 12.2, p. 406
What are the states of the halogens under standard conditions?
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular Forces
Permanent vs. induced dipole momentsDipole Forces:◦ Attractive forces between polar molecules
Figure 12.1, p. 404
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular Forces
What is the trend of boiling points of HI, HBr, HCl and HF?
IMF
–Pu
re S
ubst
ance
s
0
50
100
150
200
250
300
350
HF HCl HBr HI
Boi
ling
poin
t (K
)
12.2 Intermolecular Forces
Specific type of dipole forceHydrogen bonding (IMF – not covalent bond):◦ Special type of dipole-dipole interaction between the
hydrogen atom in a polar bond, such as N-H, O-H or F-H and an electronegative O, N, or F atom.
Figure, p. 409
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular Forces
Figure 12.7, p. 405
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular Forces
Figure 12.6, p. 408
Decreasing molar massDecreasing boiling pointNo hydrogen bonding
IMF
–Pu
re S
ubst
ance
s
Hydrogen bondingGreater IMFHigher boiling pt
12.2 Intermolecular ForcesIM
F –
Pure
Sub
stan
ces
Dispersion forces
Dipole forces
Hydrogen bonding
12.2 Intermolecular ForcesUsing IMF with pure substances:Approximating relative melting or boiling points1. Determine the intermolecular forces of the
substances (usually comparing between two different pure substances)
2. Consider the number of intermolecular forces:If they are different, then the substance with the higher number of intermolecular forces has the higher boiling pointIf they are the same, then the substance with the higher number of electrons has the higher boiling point
IMF
–Pu
re S
ubst
ance
s
12.2 Intermolecular ForcesUsing IMF with pure substances:Which has the higher boiling point?
1. Determine the IMF
2. Consider the number of intermolecular forces:
If they are different, then the substance with the higher number of intermolecular forces has the higher boiling point
If they are the same, then the substance with the higher number of electrons has the higher boiling point
IMF
–Pu
re S
ubst
ance
s
Substance Boiling Point, oC
C2H4 -104
NF3 71
C2H4
NCl3States at room temperature?
12.2 Intermolecular ForcesUsing IMF with pure substances:Which has the higher boiling point?
1. Determine the IMF
2. Consider the number of intermolecular forces:
If they are different, then the substance with the higher number of intermolecular forces has the higher boiling point
If they are the same, then the substance with the higher number of electrons has the higher boiling point
IMF
–Pu
re S
ubst
ance
s
Substance Boiling Point, oC
butanol 157
methanol 65butanol methanol
States at room temperature?
HC
O
H H
HHC
CC
CO
H H
H H
H H
H H
H
12.2 Intermolecular Forces
Figure 12.7, p. 408
IMF
–M
ixtu
res
12.2 Intermolecular Forces
Now focus on mixtures:How do we model mixtures?How do the intermolecular forces and sizes of molecules affect solubility?
We will use structure and size to assist in approximating intermolecular forces and connect this to physical propertiesThink about this like a “substitution”
IMF
–M
ixtu
res
Margin Figure, p. 409
IMF
–M
ixtu
res
12.2 Intermolecular Forces
12.2 Intermolecular ForcesUsing IMF with mixtures:Approximating solubility1. Determine the intermolecular forces of the substances
(usually considering the solubility of two pure substances)
2. Determine the relative size of the two molecules (same or different)If both (IMF and size) are the same, then we would approximate that the substances are solubleIf both (IMF and size) are different, then we could approximate that the substances are insolubleIf one (IMF or size) are the same, then we would approximate that the substances are partially soluble
IMF
–M
ixtu
res
12.2 Intermolecular ForcesUsing IMF with mixtures:What is the solubility of the two substances?
1. Determine the IMF
2. Determine the relative size of the two molecules (same or different)
If both (IMF and size) are the same, then the substances are solubleIf both (IMF and size) are different, then the substances are insolubleIf one (IMF or size) are the same, then the substances are partially soluble
IMF
–M
ixtu
res
Solubility (g in 100g)
Infinitely (miscible)
watermethanol What does this look like?
HC
O
H H
H
12.2 Intermolecular ForcesUsing IMF with mixtures:What is the solubility of the two substances?
1. Determine the IMF
2. Determine the relative size of the two molecules (same or different)
If both (IMF and size) are the same, then the substances are solubleIf both (IMF and size) are different, then the substances are insolubleIf one (IMF or size) are the same, then the substances are partially soluble
IMF
–M
ixtu
res
Solubility (g in 100g)
8.88
water What does this look like?butanol
HC
CC
CO
H H
H H
H H
H H
H
12.2 Intermolecular ForcesIM
F –
Mix
ture
s
What do these look like?
Alcohol Solubility (g in 100g H2O)
Infinitely (miscible)
8.88
2.73
0.602
0.174
12.2 Intermolecular ForcesUsing IMF with mixtures:Determining IMF that exist between the substances:◦ Dispersion forces (or induced dipole-induced dipole)
between all substances in a solution.◦ A nonpolar and a polar substance would have induced
dipole-dipole forces◦ A polar and a polar substance would have dipole-dipole
forces◦ A ionic and a nonpolar substance would have ion-induced
dipole forces◦ A ionic and a polar substance would have ion-dipole
forces
IMF
–M
ixtu
res
12.2 Intermolecular ForcesUsing IMF with mixtures:What are the IMF between the two substances?
Determine the IMFDispersion forces (or induced dipole-induced dipole) between all substances in a solution.A nonpolar and a polar substance would have induced dipole-dipole forcesA polar and a polar substance would have dipole-dipole forcesA ionic and a nonpolar substance would have ion-induced dipole forcesA ionic and a polar substance would have ion-dipole forces
IMF
–M
ixtu
res
watermethanol
HC
O
H H
H
dipole-dipole forcesdispersion forces
12.2 Intermolecular ForcesUsing IMF with mixtures:What are the IMF between the two substances?
Determine the IMFDispersion forces (or induced dipole-induced dipole) between all substances in a solution.A nonpolar and a polar substance would have induced dipole-dipole forcesA polar and a polar substance would have dipole-dipole forcesA ionic and a nonpolar substance would have ion-induced dipole forcesA ionic and a polar substance would have ion-dipole forces
IMF
–M
ixtu
res
waterSalt, NaCl
ion-dipole forcesdispersion forces
Which molecule does not have the intermolecular force of hydrogen bonding as a pure substance?
I II III
(A)Only I (B) I and II(C) I and III (D) II and III
Cha
pter
12
–Pr
actic
e
12.3 Properties of Liquids
How is structure related to other properties of liquids (surface tension, viscosity)?What is surface tension?◦ The amount of energy required
to stretch or increase the surface of a liquid by a unit area
◦ Would you expect higher intermolecular forces, higher surface tension
Figure 12.8, p. 410
Figure 12.10, p. 411
12.3 Properties of LiquidsWhat is cohesion?◦ The IMF attraction between like
molecules
What is adhesion?◦ An attraction between unlike
molecules
◦ Would expect similar intermolecular forces, better adhesion
How can these work together?
Capillary action
Adhesion and cohesion
capillary action
Figure 12.10, p. 411
12.3 Properties of LiquidsWhat is cohesion?◦ The IMF attraction between like
molecules
What is adhesion?◦ An attraction between unlike
molecules
◦ Would expect similar intermolecular forces, better adhesion
What if these don’t work together?
Only Cohesionno capillary
action
12.3 Properties of Liquids
What is viscosity?◦ A measure of a fluid’s resistance to flow
◦ Would expect higher intermolecular forces, higher viscosity
Table 12.3, p. 411
Figure 12.13, p. 413
12.3 Properties of LiquidsHow is water unique?
Figures 12.131 and 12.13 p. 412-413
12.3 Properties of LiquidsMaximum Density
40C
Which beaker contains water?
12.4 Crystal Structure
How do we model solids?What are two general ways solids form?Can we model both forms?
Figure 12.14, p. 414
Figure 12.15, p. 414
12.4 Crystal Structure
Figure 12.16, p. 415
12.4 Crystal Structure
12.4 Crystal StructureHow do we determine the number of atoms per unit cell?
PositionFraction of atom in that position
Number of atom(s) in that
position
Number of atoms per unit
cell in that position
On a corner 1/8 8 1On a faceIn the center
Figure 12.18, p. 416
12.4 Crystal StructureHow do we determine the number of atoms per unit cell?
PositionFraction of atom in that position
Number of atom(s) in that
position
Number of atoms per unit
cell in that position
On a corner 1/8 8 1On a face 1/2 6 3In the center
Figure 12.18, p. 416
12.4 Crystal StructureHow do we determine the number of atoms per unit cell?
PositionFraction of atom in that position
Number of atom(s) in that
position
Number of atoms per unit
cell in that position
On a corner 1/8 8 1On a face 1/2 6 3In the center 1 1 1
Figure 12.18, p. 416
12.4 Crystal Structure
For each simple cubic, elemental structure, we will answer:
1. Number of atoms per unit cell2. What is the length of one side of this crystal
(in terms of the radius of the atom)?3. What is the volume of this crystal (assuming
the atoms are spheres)?4. What is the packing efficiency of this crystal?
Figure 12.19, p. 416
12.4 Crystal Structure
Figure 12.19, p. 416
12.4 Crystal Structure
Figure 12.19, p. 416
12.4 Crystal Structure
Eu crystallized in a body-centered cubic cell. The density of Eu is 5.26 g·cm–3, what is the unit cell edge length in pm?
Prac
tice
exer
cise
–cr
ysta
l str
uctu
res
For this we will need to calculate:
- The number of atoms per unit cell.
- The mass (in g) of these atoms.
- The volume of the unit cell in cm3.
- The length of one side of the unit cell in cm.
Because Eu is body-centered cubic, we can calculate the number of atoms per unit cell as 2.
Using the density, the molar mass, NA, and the number of atoms per unit cell, we can calculate the volume of the unit cell.
Because this is a cubic unit cell, the length of one side is:
− −⎛ ⎞⎛ ⎞⎛ ⎞⎛ ⎞ = ×⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟×⎝ ⎠⎝ ⎠⎝ ⎠⎝ ⎠
323 3
23
cm 152.0 g mol 2 atoms9.60 10 cm
5.26 g mol unit cell6.022 10 atoms
− −= × = ×3 23 3 83length of one side (BCC) = Volume 9.60 10 cm 4.58 10 cm
Prac
tice
exer
cise
–cr
ysta
l str
uctu
res
Metallic copper crystallizes in a cubic structure. The length of the edge of the unit cell is 361 pm. If copper has a density of 8.96 g·cm–3, which type of unit cell is present in this sample?
Prac
tice
exer
cise
–cr
ysta
l str
uctu
res
For this we will need to calculate:
- The volume of the unit cell in cm3.
- The mass of the unit cell (using density).
- The number of atoms per unit cell (using NA).
Because copper has a unit cell with an edge length of 361 pm, we will first convert into cm (to use the density) and then cube for the volume of the unit cell.
The side length is 361 pm = 361x10-12 m = 361x10-10 cm.
The volume of the unit cell is (361x10-10 cm)3 = 4.70x10-23 cm3
The number of atoms per unit cell is:
4 atoms per unit cell indicates a face-centered cubic packing.
−−⎛ ⎞ ⎛ ⎞× ×⎛ ⎞⎛ ⎞ = ⋅⎜ ⎟ ⎜ ⎟⎜ ⎟⎜ ⎟
⎝ ⎠⎝ ⎠⎝ ⎠ ⎝ ⎠
23 3 231
3
4.70 10 cm 8.96 g mol 6.022 10 atoms4 atoms unit cell
unit cell 63.55 g molcm
Prac
tice
exer
cise
–cr
ysta
l str
uctu
res
When aluminum crystallizes, it forms face-centered cubic cells. The atomic radius of an Al atom is 143 pm. What is the density of metallic aluminum?
Prac
tice
exer
cise
–cr
ysta
l str
uctu
res
For this we will need to calculate:
- The length of one side of the unit cell in cm.
- The volume of the unit cell in cm3.
- The number of atoms per unit cell.
- The mass (in g) of these atoms.
Because aluminum is face-centered cubic, using the radius, we can calculate the length of one side of the cube.
The radius is 143 pm = 143x10-12 m = 143x10-10 cm.
The face-centered cubic unit cell has the length of one side equal to 4.04x10-8 cm.
The volume of the unit cell is 6.59x10-23 cm3
There are 4 atoms per unit cell.
The density is:
323 23 3
26.98 g mol 4 atoms unit cell 2.72 g cmmol unit cell6.022 10 atoms 6.59 10 cm
−−
⎛ ⎞⎛ ⎞⎛ ⎞⎛ ⎞ = ⋅⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟× ×⎝ ⎠⎝ ⎠⎝ ⎠⎝ ⎠
length of one side (FCC) = 8r
Prac
tice
exer
cise
–cr
ysta
l str
uctu
res
12.5 Bonding in SolidsWhat are the main classes of crystalline solids?◦ Ionic◦ Covalent◦ Molecular◦ Metallic
How do the general properties help us differentiate between these classes?◦ Type of bonding in the
solid◦ Melting points◦ Conductivity (heat or
electricity)◦ Solubility (in polar or
nonpolar solvents)
12.5 Bonding in Solids
CsCl ZnS CaF2
Properties Ionic SolidsType of bonding in the solid electrostatic attraction
Melting points 600-2000 oC
Conductivity (heat or electricity) poor conductor
Solubility (in polar or nonpolar solvents) soluble in polar solvents
Figure 12.22, p. 420
12.5 Bonding in Solids
Properties Covalent SolidsType of bonding in the solid covalent bonds
Melting points >1000 oC
Conductivity (heat or electricity) poor conductor
Solubility (in polar or nonpolar solvents) insoluble in either type
carbonatoms
Figure 12.24, p. 422
12.5 Bonding in Solids
Properties Molecular SolidsType of bonding in the solid intermolecular forces
Melting points Low melting points
Conductivity (heat or electricity) poor conductor
Solubility (in polar or nonpolar solvents) soluble in nonpolar solvents
Margin Figure p. 421
12.5 Bonding in Solids
Properties Metallic SolidsType of bonding in the solid metallic bonding
Melting points Low to high
Conductivity (heat or electricity) good conductor
Solubility (in polar or nonpolar solvents) insoluble
Cross Section of a Metallic Crystalnucleus &inner shell e-
Mobile “sea”of e-
Figure 12.25, p. 422
12.5 Bonding in Solids
Table 12.4, p. 420
12.6 Phase Changes
What are the three phases of matter?◦ Phases are a
homogeneous part of the system in contact with other parts of the system by separated from them by a well-defined boundary.
Consider the liquid-vapor equilibrium on a particle level. How is this an equilibrium?
Figure 12.27, p. 423
12.6 Phase Changes
What is vapor pressure?◦ The pressure exerted by gaseous molecules from
when a liquid evaporates
Consider an ideal gas, how are pressure and temperature related?How is vapor pressure and temperature related?
12.6 Phase Changes
How are vapor pressure and enthalpy of vaporization related?
Table 12.5, p. 425
12.6 Phase Changes
What is the boiling point?◦ The boiling point is the temperature at which the
(equilibrium) vapor pressure of a liquid is equal to the external pressure.◦ The normal boiling point is the temperature at which
a liquid boils when the external pressure is 1 atm.
12.7 Phase Diagrams
What is a phase diagram?◦ summarizes the conditions under which a substance
exists as a solid, liquid or gas.
Consider modeling this for water:◦ What happens at 100oC and 1 atm?
What happens when temperature changesWhat happens when pressure changes
◦ What happens at 0oC and 1 atm?What happens when temperature changesWhat happens when pressure changes
12.7 Phase Diagrams
What is the triple point?◦ the only temperature and pressure at which all three
phase can be in equilibrium with one another.
What are critical temperature (Tc) and critical pressure (Pc)?◦ above which its gas form cannot be made to liquefy; no
matter how great the applied pressure. This is also the highest temperature at which a substance can exist as a liquid. The minimum pressure that must be applied to bring about liquefaction at this critical temperature is the critical pressure
12.7 Phase Diagrams
How do we model phases for a pure substance over a range of temperatures and pressures?
Figure 12.32, p. 430
12.7 Phase Diagrams
How do we model phases for a pure substance over a range of temperatures and pressures?
Figure 12.33, p. 430
Bigger PictureWe have finally connected structure (on the particle level) based on:◦ Atomic structure◦ Electronic structure◦ Bonding◦ Shape◦ Polarity
and function – properties onthe macroscopic levelWe have reason and explanation for observations
As the temperature of a liquid increases, the number of particles in the vapor phase _______________ and the vapor pressure _______________.
(A) decreases; decreases(B) decreases; increases(C) increases; decreases(D) increases; increases
Cha
pter
12
–Pr
actic
e
A metal crystallizes in a body‐centered cubic (bcc) crystal structure. If the atomic radius of the metal is 124.1 pm and the density is 7.87 g∙cm–3, what is the metal?
(A) Cd (B) F (C) Fe (D) K
43ra =
Using the phase diagram to the right, which letter indicates (only) the liquid region?(A) A (B) B(C) C (D) D