1. Chapter 11 Liquids, Solids, and Intermolecular Forces
Interparticle Forces
What properties correlate with overall strength of
What different kinds are there?
Different for ionic compounds, metals, covalent network solids (lab) and…
Molecular Substances
London
Dipole-dipole
H-bonding

2. Reminder: Nanoscopic Representations of the Three States of Matter
Chapter 11, Unnumbered Figure 1, Page 458

3. Compressibility
Tro: Chemistry: A Molecular Approach, 2/e

4. What kinds of forces hold particles together?
It depends on the particles!
Ions attract ions differently than:
molecules attract molecules or
Atoms attract atoms (if atoms are covalently bonded—covalent network solids)

5. The stronger the forces are between particles, the __________
Higher the melting point (mp)
Higher the boiling point (bp)
Higher the DHmelting
Higher the DHvaporization
Greater the Surface tension
Greater the Viscosity
Lower the vapor pressure (at a given T)

6. Table 10.2 (Zumdahl) The Melting Points of the Group 8A Elements
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10–6

7. Table 10.9 Melting Points and Enthalpies of Fusion for Several Representative Solids
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10–7

8. Big Classifications First, then get into what attracts molecules to one another
SEE EXP 17 GRID

9. Types of Solids (Tro) [only property noted is mp]
Chapter 11, Figure 11.50
Types of Crystalline Solids

10. Table 10.7 (Zumdahl) Types and Properties of Solids
Most are soluble in some solvent
Many are soluble in water
Not soluble in any solvents
Not soluble in any solvents
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10–10

11. Three Possible Intermolecular Forces (IM forces) may act between molecules (only if molecular!)
London forces act between ANY two molecules (polar or nonpolar)
Reason is not obvious (later)
Dipole-dipole forces act only between two POLAR molecules
Need to learn how to determine if a molecule is polar or nonpolar (handout)
Hydrogen bonding occurs only in very special circumstances (handout)
→ N.B. Intermolecular forces are ALL much weaker than intramolecular forces (covalent bonds)!
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12. Atomic Separations Within Molecules (Covalent Bonds) vs
Atomic Separations Within Molecules (Covalent Bonds) vs. Between Molecules (Intermolecular Interactions)
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10–12

13. Approach to Assessing Overall Strength of IM forces
First estimate the overall strength of London Forces (next slide)
Then consider if there are additional IM forces:
Dipole-Dipole (if polar)
H-bonding (special cases)
NOTE: No estimate of the strength of these two is made. Just “yes” or “no”.
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14. London Forces depend on the number of total electrons per molecule
More electrons (total), greater force of attraction
MW also correlates
Greater MW  more protons  more electrons
Correlation is only rough
Don’t overinterpret
20 vs 18 e-s about same
Shape of molecule also plays a role
NOTE: Origin of London Forces will be discussed later
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15. Invoking London forces explains the observed bp trend of the noble gases (no dipole-dipole and no H-bonding)
#e-’s per atom
2 (MM = 4)
8 (MM = 20)
18 (MM = 40)
36 (MM = 84)
54 (MM = 131)
IM forces
(London)
Click to add notes

16. Invoking London forces explains the
observed bp trend of the simple alkanes
(no dipole-dipole and no H-bonding)
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17. Must consider there may be two other types of IM forces!
London forces (always)
Dipole-dipole forces (only if polar)
Hydrogen bonding (special circumstance)
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18. Dipole-Dipole Forces Figure 10
Dipole-Dipole Forces Figure (a) The Electrostatic Interaction of Two Polar Molecules (b) The Interaction of Many Dipoles in a Condensed State
**NOTE: All + and – signs should be d+ and d- here!!
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19. NOTE: How to determine if a molecule is polar will be discussed later
Chapter 11, Figure 11.7
Dipole–Dipole Interaction

20. If other two types of forces are also present, that adds to the total IM forces
Determine if molecules are polar
Br2 vs ICl (and next slide)
similar London (70 e’s each)
Only ICl has dipole-dipole forces
 Predict ICl has stronger IM forces  higher bp (59 vs 97 C)
Determine if molecules can H-bond with one another
-“self-self” H-bonding (see board & handout)
if at least one N-H, O-H, or F-H bond
→ Must consider ALL possible forces to decide relative bp, mp, VP, etc.
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21. Example: Similar London, but Larger Dipole-Dipole Leads to Stronger (overall) IM forces and Higher bp, mp
Chapter 11, Unnumbered Table, Page 462

22. Again, greater polarity (similar London) yields greater (overall) IM forces (and bp)
Chapter 11, Figure 11.8
Dipole Moment and Boiling Point

23. Figure 10.3 a-b (a) The Polar Water Molecule (b) Hydrogen Bonding Among Water Molecules
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24. Figure 11.13 Explain these trends by approximating the IM forces
Chapter 11, Figure 11.13
Boiling Points of Group 4A and 6A Compounds

25. What causes London (dispersion) forces?
Chapter 11, Figure 11.4
Dispersion Interactions

26. Figure 10. 5 Zumdahl What causes LONDON FORCES
Figure 10.5 Zumdahl What causes LONDON FORCES? (a) An Instantaneous Dipole can Occur on Atom A, inducing a dipole on nearby Atom B. (b) The same thing can occur with nonpolar molecules
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27. http://www. yteach. co. uk/page. php/resources/view_all
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28. More Examples (Explaining bp differences)
Explain the difference in boiling points:
n-pentane, C5H12 MW: 72 amu bp = 36.2 C vs.
Neopentane, C5H12 MW: 72 amu bp = 9.5 C
dimethyl ether, CH3OCH3 MW: 46 amu bp = -25 C vs.
ethanol, CH3CH2OH MW: 46 amu bp = 79 C
Naphthalene, C10H MW: 128 amu bp = 218 C vs.
Acetic Acid, CH3CO2H MW: 60 amu bp =118 C

29. More Examples
What type of interparticle forces are present in these substances?
Ar, HCl, CaCl2
What is the most important interparticle force in teflon, CF3(CF2CF2)nCF3?
Which substance has stronger intermolecular forces?
SeO2 Vs. SO2
Which has the highest boiling point?
NaCl or HCl
Which substance has the highest freezing point?
H2O, NaCl, or HF

30. IM forces result in surface tension
And why liquid droplets are spherical!
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31. Figure Zumdahl A Molecule in the Interior of a Liquid is Attracted by the Molecules Surrounding It
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32. Surface tension examples: Liquid Mercury Forms a Convex Meniscus in a Glass Tube (unlike water) Water beads on a wax surface
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33. Back to molecular substances— How to tell if a molecule is polar
Next slide (and handouts)
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34. Polarity of Molecules (see handout #1 and Section 10.5 in Tro)

35. ...if symmetry is very high, bond dipoles can cancel out
Having polar bonds in a molecule does not necessarily result in a polar molecule…
...if symmetry is very high, bond dipoles can cancel out
Recall VSEPR geometries! (see handout, next slides)
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36. Polarity of Molecules (see handout #2)

37. Polarity of Molecules (continued)

38. (Nonpolar)
(Polar) F
Chapter 10, Unnumbered Figure 2, Page 415

39. Back to non-molecular substances
Metals
Covalent network solids
Ionic
won’t further address in this presentation—ion-ion forces are generally strong and result from Coulombic forces between charged ions.
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40. Figure The Electron Sea Model for Metals Postulates a Regular Array of Cations in a "Sea" of Valence Electrons
→ Ultra simplified, but does explain electrical conductivity, malleability, and ductility of metals
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41. Figure 10.22 The Structures of Diamond and Graphite
→ Weak inter-layer bonding explains why graphite is used in pencils! Planes “shear off” on writing.
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42. Figure The p Orbitals (a) Perpendicular to the Plane of the Carbon Ring System in Graphite can Combine to Form (b) an Extensive p-Bonding Network
→ This explains directional electrical conductivity in a crystal of graphite.
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43. Figure 10.26 The Structure of Quartz (Empirical Formula SiO2)
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