1. States of Matter and Intermolecular Forces
Chapter

2. COMPARING SOLIDS, LIQUIDS, AND GASES
The densities of solids and liquids are usually much higher than gases
The densities and molar volumes of solids and liquids are more similar than they are to the gas state
This is because molecules in liquid water are close to each other (nearly touching) while in it's gaseous state, molecules are separated by large distances
Water displays atypical behavior by having a less dense solid than the liquid state
This is due to the unique crystal structure formed in ice causing the molecules to move slightly apart
The main difference between liquids and solids comes from freedom of movement
Even though liquid molecules are close, thermal energy overcomes the attractions between them, allowing them to move more freely

3. COMPARING SOLIDS, LIQUIDS, AND GASES
In solids, however, atoms or molecules are essentially locked in place, only vibrating back and forth about a fixed point
Liquids have the ability to assume the shape of their containers because atoms or molecules in liquids are free to flow and move
The same could be said to for gases, but to a more extreme degree
Solids have a fixed shape because they lack the ability to move
Like solids, liquids have a definite volume due to the close proximity of atoms or molecules
Solids can be crystalline (where atoms or molecules are arranged in a well-ordered three dimensional array) or amorphous (where atoms or molecule that have no consistent order)

4. STATE CHANGES STATE CHANGES
The states of substances can be transformed by adjusting temperature, pressure, or both
For example, liquid water is changed into ice by lowering the temperature and ice is melted by raising the temperature
A way to change gaseous water into liquid is by increasing pressure
Increasing pressure results in a more dense substance (gas to liquid to solid)
Example, when you buy a tank of propane to use as fuel, the inside of the tank contains pressurized liquid propane. When you unscrew the tank, you lower the pressure in the tank for a moment. This causes a state change from a liquid to now a gas
This is a more efficient way to store propane because as a liquid it occupies less space

5. INTERMOLECULAR FORCES
Intermolecular forces - the forces that hold together a substance
Because of this, IMFs determine whether a substance is solid, liquid or gaseous at room temperature
Moderate to to strong IMFs tend to result in liquids and solids (high melting and boiling points)
Weak IMFs typically result in gases (low melting and boiling points)
Intermolecular forces originate from the interactions between charges (both temporary and partial) on molecules (or atoms and ions)
Consistent with Coulomb’s law, molecules with partial or temporary charges are attracted to each other because their potential energy decreases as they get closer
Because of the smaller magnitude of charge, IMFs are significantly less strong than ionic or covalent bonds

6. DISPERSION FORCE
Dispersion Force (Also known as London Force) is the IMF present in all molecules and atoms
They result from slight changes in electron distribution within molecules or atoms
This uneven electron distribution exists at any single moment
This brief even distribution is referred to as a instantaneous dipole or temporary dipole
The magnitude of the dispersion force depends on how easily electrons can move (polarize) into a temporary dipole.
Larger electron cloud = stronger dispersion force
If all other variables are kept constant, higher molar mass usually results in the stronger dispersion force and in turn a higher boiling point
Keep in mind: shape matters! Long molecules with large surfaces for bonding will have higher boiling points

7. Which halogen has the highest boiling point?
Cl2
Br2 I2

9. DIPOLE-DIPOLE FORCE
The dipole-dipole force is present in all polar molecules
Polar molecules have electron rich regions (partially negative) and electron poor areas (partially positive) resulting in a permanent dipole that interact with other polar molecules
Because of this, polar molecules have higher boiling points than nonpolar molecules with similar molar mass
Miscibility: the ability to mix without separating into two states
As a general rule, polar liquids are miscible with other polar molecules and nonpolar molecule are miscible with nonpolar molecules
This is why (polar) water does not mix with (nonpolar) oil

11. HYDROGEN BONDING
Hydrogen bonding occurs when polar molecules containing hydrogen bond directly with atoms with large electronegativity
Most importantly fluorine, oxygen, or nitrogen
Examples: HF, NH3, and H20
A hydrogen bond can be thought of as a super dipole-dipole force making it quite strong
The strength of hydrogen bonds are derived from the large electronegativity difference between hydrogen and any of these other electronegative atoms
Also, because all of these atoms are quite small, they can get very close together
Hydrogen bonds should not be confused with chemical bonds
Chemical bonds = bonds between two (or more) atoms within a molecule
Hydrogen bonds = bonds between two (or more) molecules

12. ION-DIPOLE FORCE
The ion-dipole force occurs when an ionic compound is mixed with a polar compound
This is particularly important as it relates to aqueous solutions of ionic compounds
Example: When sodium chloride is mixed with water, the sodium and chloride ions interact with the water molecules via ion-dipole forces. The positive sodium ions interact with the negative poles of water molecules, while the negative chloride ions interact with the positive poles of the water molecules.
Ion dipole forces are the strongest of the types of IMFs and are responsible for the ability of ionic substances to form solutions with water

13. Determine the kinds of intermolecular forces that are present in each element or compound.
HCl
H20
Br2 He

14. HCl
H20
Br2 He
Dispersion, dipole-dipole
Dispersion, dipole-dipole, hydrogen bonding
Dispersion