1. Chapter 10: Liquids and Solids

2. Intermolecular Forces
Dipole Attraction - Positive/negative center of charge in polar molecules attract each other
1% of the strength of ionic/covalent bonds
Hydrogen Bonding - Very strong dipole attraction between a hydrogen and very electronegative atom
More electronegative = stronger bond
London Dispersion Forces - A result of the “instantaneous dipole”, not all electrons are evenly distributed throughout the nucleus
Affects electron dispersion in nearby atoms
Stronger for larger atoms, due to more electrons
Polarizability - How easy it is to change the electron distribution in atoms

3. Liquids
Surface Tension - Resistance of a liquid to increasing surface area.
Greater with molecules with larger intermolecular forces
Capillary Action - Liquid’s tendency to rise in a narrow tube
Common in polar molecules
Molecules pulled up tube by charge differences between liquid and the tube
The molecules above attract the ones below through cohesion, and the liquid is pulled up the tube
Viscosity - A liquid’s resistance to flow
Larger intermolecular forces = higher viscosity
Large molecules can become entangled with each other

4. Structures and Types of Solids
Two main categories of solids:
Crystalline solids - Regular arrangement of atoms/molecules
Amorphous solids - Lack of order in arrangement
Lattice - Arrangement of components in a crystalline solid
Unit cell - Smallest repeating component of a lattice
Types of crystalline solids:
Ionic solids - Ions present at lattice points
Molecular solids - Covalently bonded molecules at lattice points
Atomic solids - Single atoms at lattice points
Metallic solids - Delocalized non-directional covalent bonding at lattice points
Network solids - Strong directional covalent bonds making very large molecules
Group 8A solids - Noble gas elements attracted to each other through dispersion forces

5. Network Atomic Solids
Network solids - Atomic solids which contain directional covalent bonds
Similar to a very large molecule
Generally brittle, and do not conduct electricity
Diamond - Hardest naturally occurring substance
Tetrahedral unit cell, sp3 hybridized
Graphite - Slippery and conductive
Layers of carbon “sheets” in hexagonal rings, sp2 hybridized
Remaining 2p orbital creates delocalized π bonds with sheets above/below
Accounts for slipperiness, the sheets are able to easily move laterally to each other due to lack of strong bonding
Silica - Main silicon/oxygen compound
Silicon unable to form strong π bonds with oxygen due to its larger size
Forms single bonds with 4 oxygen atoms
Silicates - Have oxygen/silicon ratios greater than 2:1, contain silicon/oxygen anions
Cations required to balance the negative charges
Glass - Amorphous solid resulting from heating silica

6. Molecular/Ionic Solids
Molecular solids - Solid in which the lattice positions are occupied by molecules
Very strong bonding within molecules, but not as much between
Ionic Solids - These solids have high melting points as a result of the strong attractions exist between negatively charged anions and positively charged cations (ionic bonds).
The structure of ionic solids is represented by having the smaller cations contained within the spaces between anions. The possible structures are trigonal, tetrahedral, or octahedral.

7. Vapor Pressure Vapor Pressure - Pressure of vapor at equilibrium
Determined by magnitude of intermolecular forces
High vapor pressure liquids are generally volatile - evaporate quickly from open container
Increases with temperature
If the vapor pressure at one temperature is known, the vapor pressure at another temperature can be determined by the equation:

8. Changes of State
Changes of state can be illustrated by a heating curve - a temperature vs. time graph:
Melting point is when the liquid and solid forms of a substance have the same vapor pressure
Boiling point is when the liquid’s vapor pressure is equal to the atmospheric pressure
Supercooling - When a liquid is cooled below its freezing point, yet remains a liquid
This is due to the molecules not necessarily forming into an organized structure
Superheating - Liquid heated above boiling point, yet remains a liquid
In order for bubbles to form, high-energy molecules must gather in the same area at once, which may not always occur

9. Phase Diagrams
Phase Diagrams are used to represent the state of a substance at any given temperature and pressure. Most phase diagrams contain three lines, each line representing the boundary between two phases.
An important point is known as the triple point. At this temperature and pressure, all three phases exist at the same time. Finally, another important point is the critical point. At the critical temperature, if the temperature were to be any higher, no amount of pressure would be able to cause the substance to liquify. Meanwhile, the critical pressure is the pressure required to liquify the substance at the critical temperature. Combining the two results in the critical point.

10. Review Questions
1. Why does the size of atoms/molecules affect the strength of London Dispersion Forces?
2. Describe the difference in structure between graphite and diamond
3. Sort the following from least to greatest melting point: Cl2 , NaCl, PCl3(polar)