Overview
This lecture reviews major first-semester general chemistry topics, focusing on core concepts, calculations, and problem-solving strategies commonly tested in college or AP/IB Chemistry.
Atomic Structure & Ions
- The atomic number equals the number of protons in an atom.
- Mass number = protons + neutrons; neutrons = mass number − atomic number.
- Ions have unequal protons and electrons; cations have more protons than electrons.
Chemical Nomenclature & Formulas
- Ionic compounds (metal + nonmetal): do not use prefixes (e.g., sodium chloride).
- Molecular compounds (nonmetals): use prefixes (e.g., dinitrogen pentoxide for N₂O₅).
- Common prefixes: mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), etc.
Stoichiometry & Yield
- Percent composition: (mass of element/total molar mass) × 100%.
- Limiting reactant determines maximum product yield.
- Theoretical yield: calculated from stoichiometry; percent yield = (actual/theoretical) × 100%.
Solution Concentrations & Dilutions
- Molarity (M) = moles solute/liters solution; convert grams to moles using molar mass.
- Dilution formula: M₁V₁ = M₂V₂; added water = final volume − initial volume.
- Molality (m) = moles solute/kg solvent; used in colligative properties.
Gas Laws
- Combined gas law: P₁V₁/T₁ = P₂V₂/T₂; keep units consistent.
- Ideal gas law: PV = nRT (R = 0.08206 L·atm/mol·K).
- At STP, 1 mole gas occupies 22.4 L; density = molar mass/22.4.
- Partial pressure: use balanced equations and PV = nRT for calculations.
Thermochemistry & Phase Changes
- q = mCΔT (heat = mass × specific heat × temp change); ΔH = ΣH(products) − ΣH(reactants).
- Phase changes:
- Melting (solid→liquid), vaporization (liquid→gas), sublimation (solid→gas): endothermic.
- Freezing (liquid→solid), condensation (gas→liquid), deposition (gas→solid): exothermic.
Solution Properties & Colligative Effects
- Boiling point elevation/freezing point depression: ΔT = K × m × i (i = number of ions per formula).
- Osmotic pressure: Π = MRTi; use molarity derived from grams and volume.
- Vapor pressure lowering: Pₛₒₗ = χₛₒₗᵥₑₙₜ × P°ₛₒₗᵥₑₙₜ (χ = mole fraction).
Electronic Structure & Quantum Numbers
- Electron configurations sum to atomic number (e.g., 1s²2s²2p⁵ for F).
- Quantum numbers:
- n = energy level, l = sublevel (s=0, p=1, d=2, f=3), ml = orbital, ms = spin (±½).
- Number of orbitals in level n: n².
Periodic Trends & Bonding
- Ionization energy increases up and to the right; helium has the highest.
- Atomic radius increases down/left; electronegativity increases up/right to fluorine.
- Hydrogen bonding > dipole-dipole > London forces (in strength).
- Polar molecules: have net dipole moments due to differences in electronegativity and geometry.
Molecular Geometry & Hybridization
- Shapes:
- Tetrahedral: 109.5° (e.g., CH₄).
- Trigonal planar: 120° (e.g., BF₃).
- Bent: <120° or <109.5° (e.g., H₂O).
- sp³ hybridization: 4 groups (e.g., H₂O).
Energy & Light
- Energy of photon: E = hc/λ (h = Planck’s constant, c = speed of light, λ = wavelength).
- Order of increasing wavelength: gamma < x-ray < UV < visible < IR < microwave < radio.
Key Terms & Definitions
- Molarity (M) — moles of solute per liter of solution.
- Molality (m) — moles of solute per kilogram of solvent.
- Limiting Reactant — reactant completely consumed first in a reaction.
- Percent Yield — (actual yield/theoretical yield) × 100%.
- STP — standard temperature and pressure (0°C, 1 atm).
- Colligative Properties — depend on solute particle number (e.g., boiling point elevation).
- Quantum Numbers — describe electrons’ energy, shape, orientation, and spin.
Action Items / Next Steps
- Review key equations and add them to your formula sheet.
- Practice naming compounds and writing formulas.
- Solve practice problems for stoichiometry, gas laws, and solution concentrations.
- Draw Lewis structures and predict molecular geometry for practice molecules.
- Memorize periodic trends and key definitions.