Gases, Liquids, Solids, and Attractive Forces

LO 7.1: Gases and Gas Laws
- Convert pressure units.
- Apply the kinetic molecular theory of gases.
- Apply and solve problems using:
- Boyle’s law.
- Charles’s law.
- Gay-Lussac’s law.
- Combined gas law.
- Apply the relationships found in the ideal gas law.
- Note: All temperatures must be converted to Kelvin.

LO 7.2: Liquids and Solids: Predicting Properties through Attractive Forces
- Describe the five types of attractive forces present in compounds:
- London forces.
- Dipole-dipole attraction.
- Hydrogen bonding interactions.
- Ion-dipole attraction.
- Ionic attraction (salt bridge).
- Determine the attractive forces present in a compound from its chemical structure.
- Draw hydrogen bonds between compounds that can hydrogen bond.
- Describe the changes in the states of matter.
- Predict relative boiling points for liquids based on the attractive forces present.
- Predict relative vapor pressures for liquids based on the attractive forces present.

Changes of State and Attractive Forces
- As a substance is heated, the particles begin to move faster, causing their interactions to become less significant.
- These transitions are known as changes of state:
- Freezing and melting (between liquids and solids).
- Evaporation and condensation (between liquids and gases).
- Sublimation and deposition (between solids and gases).
Understanding vapor pressure and boiling points
- When a liquid is in a closed container, some molecules evaporate and become vapor.
- An equilibrium state is reached, and the pressure from these molecules is called vapor pressure.
- Each substance has a characteristic vapor pressure that changes with temperature.
- The boiling point is defined as the temperature at which the vapor pressure equals atmospheric pressure.
Boiling Process
- During boiling, all molecules in a liquid need sufficient energy to displace gas molecules at the liquid's surface.
- Molecules in the liquid must overcome intermolecular attractive forces to transition to gas.

By understanding attractive forces between molecules, predictions can be made on:
- Boiling point.
- Melting point.
- Vapor pressure.
- Solubility.
Types of Attractive Forces
- Attractive forces are generally due to the interactions between electron-rich and electron-poor areas within and between molecules:
- If between two molecules, it's termed intermolecular interaction.
- If within a molecule, it's referred to as intramolecular interaction.
Comparison of Forces
- London Forces (Induced Dipole/Dispersion Force): Occur momentarily via uneven electron distribution.
- Weakest attractive force.
- Dipole-Dipole Attraction: Found in polar molecules with permanent dipoles resulting from electronegativity differences.
- Hydrogen Bonding: Stronger than dipole-dipole attraction, occurs between a polarized hydrogen and an electron-rich atom like N, O, or F.
- Capable of occurring between different molecules or within a single molecule.
- Ion-Dipole Attraction: Predominantly seen in ionic compounds like salt interacting with polar solvents such as water.
- Stronger than hydrogen bonds.
- Ionic Attraction: Exists between oppositely charged ions and is the strongest attractive force, often forming salt bridges in biomolecules.

Alkanes
- Nonpolar alkanes exhibit only London forces; straight-chain alkanes with more carbons have higher boiling points due to a larger surface area for stronger attractions between molecules.
- Examples of boiling points for alkanes are provided:
  - Methane (CH4): -161°C
  - Ethane (C2H6): -89°C
  - Propane (C3H8): -42°C
  - Butane (C4H10): -0.5°C
  - Pentane (C5H12): 36°C
  - Hexane (C6H14): 69°C
  - Heptane (C7H16): 98°C
  - Octane (C8H18): 125°C
  - Nonane (C9H20): 151°C
  - Decane (C10H22): 174°C
- Branched alkanes have lesser surface contact than straight-chain alkanes, resulting in lower boiling points and higher vapor pressures under similar carbon counts.
Melting Points Trends
- Melting points align with boiling points; strong and numerous attractive forces lead to higher melting points.
- Nonpolar molecules with larger surface areas generally lead to lower vapor pressures and higher melting points.

Golden Rule of Solubility: "Like dissolves like" indicates that similar molecules will dissolve in each other based on polarity similarities.
- Hydrophilic: Water-loving (polar compounds).
- Hydrophobic: Water-hating (nonpolar compounds).
Predicting Solubility
- Nonpolar compounds (like oils) are attracted via London forces, while water exhibits stronger dipole-dipole and hydrogen bonding interactions, explaining their immiscibility.
- Polar compounds (e.g., sucrose) can dissolve in water due to interaction capabilities involving dipole-dipole and hydrogen bonding.
- Ionic compounds can dissolve when multiple water molecules surround ions, an effect called hydration, enhancing their solubility beyond ionic bond strength.

Amphipathic Molecules: Fatty acids, containing both polar and nonpolar sections.
- Soaps, derived from fatty acids, have polar ionic heads and nonpolar hydrocarbon tails which allow them to act as emulsifiers, suspending nonpolar and polar substances.

Fats vs. Oils:
- Fats are solid at room temperature; oils are liquids.
- Both belong to triglycerides, differing mainly in physical state.
- Examples like triglyceride composition illustrate the structure formed by glycerol and three fatty acids.
Phospholipid Structure:
- Phospholipids form bilayers essential for cell membranes, with polar head groups facing the aqueous environment and nonpolar tails oriented inward to protect from water.
- The fluid mosaic model describes how proteins and cholesterol interact within this lipid structure, modulating membrane rigidity and fluidity while performing critical functions.