Unit 3: Properties of Substances & Mixtures

Intramolecular Forces:
- Definition: Forces that occur within a molecule, binding the atoms together.
- Types: Strong forces including Covalent Bonds, Ionic Bonds, and Metallic Bonds.
Intermolecular Forces:
- Definition: Forces that happen between molecules; these hold the molecules together.
- Types: Generally weaker forces including Hydrogen Bonds, Dipole-Dipole Interactions, London Dispersion Forces.

Strength of Forces from Weakest to Strongest:
- London Dispersion Forces
- Dipole-Induced Dipole Interactions
- Dipole-Dipole Interactions
- Hydrogen Bonding
- Covalent Bonding
- Ionic Bonding

General Properties:
- Boiling Point Influences:
- Low boiling point indicates a likelihood for particles to change from liquid to gas.
- Weaker intermolecular forces (IMFs) lead to lower melting points.
- Lower boiling point results in more vapor and higher vapor pressure.
- Higher boiling point correlates with slow evaporation rates.
- When IMFs are equivalent, molecular mass must be considered: Heavier molecules exhibit higher boiling points.
Behavior of IMFs:
- Strong IMFs result in high boiling points and low vapor pressures.
- Weak IMFs lead to low boiling points and high vapor pressures.

Nature of Forces:
- The weakest of all intermolecular forces present in all substances.
- These forces are often neglected when stronger interactions are present.
Mechanism:
- Electrons within all atoms are in constant motion; this motion can lead to charge distributions that are momentarily uneven.
- A temporary dipole arises from these charge fluctuations, creating regions of partial positive and negative charges.
Induced Dipoles:
- If a temporary dipole is near another atom, it can induce a dipole in that atom, establishing weak attractions between neighboring atoms.
Coulomb’s Law:
- The strength of London forces depends on the magnitude of the charges (q1 and q2) and the distance between them (r²).
- Larger atoms create larger partial charges, resulting in stronger London forces due to increased induced dipoles.

In larger molecules or atoms, London dispersion forces increase because larger partial charges lead to stronger induced dipoles.
Alkane Example:
- Identical partial charges are present amongst similar sized alkanes, leading to equal attractions. Larger molecules have increased London forces.
- Structural Consideration: Branched alkanes have smaller surface areas compared to straight-chain isomers, leading to weaker London forces due to fewer attractions.

Dipole-Induced Dipole Interaction:
- Present between polar and nonpolar molecules, resulting in weak attraction when a polar molecule disturbs the electron arrangement in a nonpolar molecule.
- Strength increases with the magnitude of the polar molecule's dipole.

General Properties:
- Generally stronger than London dispersion forces among equivalent molecules (similar atomic sizes and structures).

Defined as a specific type of dipole-dipole interaction involving hydrogen bonded to highly electronegative atoms (F, O, N).
Hydrogen bonds are notably stronger than typical dipole-dipole interactions and have significant effects on boiling points and solubility.

Various factors influence boiling points:
- A comparison of the boiling points of various molecules demonstrates the impact of functional groups and intermolecular forces.

Key examples:
- Carbonyl Group (C=O) in aldehydes/ketones makes molecules polar and promotes dipole-dipole interactions.
- Hydroxyl Group (O-H) in alcohols promotes hydrogen bonding, vastly affecting their boiling points.

Water Solubility Consideration:
- Substances with stronger IMFs or polar characteristics tend to be more soluble in polar solvents like water.

Ion-Dipole Interaction:
- Attractive forces arising from electrostatic interactions between an ion and a dipole of a neutral molecule.
- Present in ionic solutions (e.g., NaCl in water).
Examples and Problem Solving:
- Real-world examples demonstrate the influences of intermolecular forces on boiling points, solubility, and other physical properties of substances.
Analytical scenarios given include comparing behavior and calculating changes in states due to temperature and pressure changes as per gas laws.

Compare values and interactions of different intermolecular forces from Ion-Dipole, H-bonding, to London dispersion.
Notable points include how the strengths of intermolecular forces directly relate to boiling points, solubility, and other physical properties.

Recap the properties of solids, liquids, and gases, emphasizing the factors affecting boiling points, solubility, and the behavior of substances under varying temperatures.

Covalent Network Solids: Strongly bonded, high melting points, hard, nonconductive.
Ionic Solids: Formed from ionic bonds; hard, brittle, high melting points, conduct in solution.
Metallic Solids: Varying m.p., malleable, conductive due to delocalized electrons.
Polymers: Long chains with varying properties based on IMF interactions.
Molecular Solids: Typically soft, associated with weaker IMFs.

Explore differences in structure and particle behavior across solid, liquid, and gas phases. Emphasize temperature and pressure's role on behavior and state transitions, relating to kinetic molecular theory.
Analyze and understand the Ideal Gas Law as it relates to gas behavior under various conditions.
Explore deviations from ideal behavior, focusing on factors like temperature and pressure, which highlight real gas interactions versus ideal predictions.