AP Chemistry Exam Review Flashcards

VSEPR Theory

• VSEPR (Valence Shell Electron Pair Repulsion) Theory predicts the geometry of molecules based on the repulsion between electron domains around a central atom.

• Electron domains include bonding pairs and lone pairs of electrons. Molecular geometry is determined by minimizing these repulsive forces.

• The following table summarizes the relationship between the number of atoms touching a central atom, the number of lone pairs, the resulting geometry, and the bond angle:

  • 4 atoms, 0 lone pairs: Tetrahedral, 109.5° (e.g., CH_4)

  • 3 atoms, 1 lone pair: Trigonal Pyramidal, ≈ 109.5° (e.g., NH_3). The lone pair compresses the bond angle slightly.

  • 2 atoms, 2 lone pairs: Bent, ≈ 109.5° (e.g., H_2O). The two lone pairs cause greater compression of the bond angle.

  • 3 atoms, 0 lone pairs: Trigonal Planar, 120° (e.g., BF_3)

  • 2 atoms, 1 lone pair: Bent / Angular, ≈ 120° (e.g., SO_2). The lone pair reduces the bond angle from the ideal 120°.

  • 2 atoms, 0 lone pairs: Linear, 180° (e.g., CO_2)

  • 5 atoms, 0 lone pairs: Trigonal Bipyramidal, 90° & 120° (e.g., PCl_5). Axial and equatorial positions are distinct.

  • 4 atoms, 1 lone pair: See-saw, ≈ 90° & 120° (e.g., SF_4). Lone pair occupies an equatorial position to minimize repulsion.

  • 3 atoms, 2 lone pairs: T-shaped, ≈ 90° (e.g., ClF_3). Lone pairs occupy equatorial positions.

  • 6 atoms, 0 lone pairs: Octahedral, 90° (e.g., SF_6)

  • 5 atoms, 1 lone pair: Square Pyramidal, ≈ 90° (e.g., BrF_5). The lone pair distorts the shape.

  • 4 atoms, 2 lone pairs: Square Planar, 90° (e.g., XeF_4). The two lone pairs are trans to each other.

Hybridization

• Hybridization is the concept of mixing atomic orbitals into new hybrid orbitals suitable for the pairing of electrons to form chemical bonds in valence bond theory.

• Electron Domains vs. Hybridization:

  • 2 electron domains: sp (e.g., BeCl_2)

  • 3 electron domains: sp2 (e.g., BF_3)

  • 4 electron domains: sp3 (e.g., CH_4)

Hydrogen Bonding

• Hydrogen bonding is a type of intermolecular force that occurs in molecules with O–H, N–H, or F–H bonds.

• These bonds are highly polarized, creating a partial positive charge on the hydrogen atom and a partial negative charge on the electronegative atom (O, N, or F).

• Hydrogen bonds are relatively strong intermolecular forces and play a crucial role in determining the properties of substances like water.

Effects of Radiation on Atoms and Molecules

• Microwave radiation causes molecules to rotate. This is the principle behind microwave ovens.

• Infrared radiation causes molecules to vibrate. Absorption of infrared radiation leads to increased molecular motion and heat.

• Ultraviolet and visible light causes electrons to be promoted to higher energy levels, can ionize atoms, or break covalent bonds. High-energy UV radiation can cause photochemical reactions and damage biological molecules like DNA.

Simple Solubility Rules

• Any ionic compound containing Na^+, K^+, or NH_4^+ ions is soluble in water. These ions generally form soluble salts.

• Any ionic compound containing the NO_3^- ion is soluble in water. Nitrates are generally soluble.

• Chlorides (Cl^-), bromides (Br^-), and iodides (I^-) are generally soluble, except when combined with Ag^+, Pb^{2+}, and Hg_2^{2+}.

• Sulfates (SO_4^{2-}) are generally soluble, except with Sr^{2+}, Ba^{2+}, Pb^{2+}, and Ca^{2+}.

• Hydroxides (OH^-) are generally insoluble, except with Group 1 cations, Sr^{2+}, and Ba^{2+}. Ca(OH)_2 is slightly soluble.

• Sulfides (S^{2-}), carbonates (CO3^{2-}), phosphates (PO4^{3-}), and chromates (CrO4^{2-}) are generally insoluble, except with Group 1 cations and NH4^+.

Kinetics

• Integrated Rate Laws: These laws relate the concentration of reactants to time for different reaction orders.

  • 0 order: [A] vs time is a straight line. The rate is independent of reactant concentration: Rate = k.

  • 1st order: ln[A] vs time is a straight line. The rate is directly proportional to reactant concentration: Rate = k[A].

  • 2nd order: 1/[A] vs time is a straight line. The rate is proportional to the square of reactant concentration: Rate = k[A]^2.

Thermochemistry

• Enthalpy Change: \Delta H = \Sigma H{\text{bonds broken}} – \Sigma H{\text{bonds formed}} (LEFT SIDE – RIGHT SIDE). Breaking bonds requires energy (endothermic, positive H), and forming bonds releases energy (exothermic, negative H).

• Percent error = \frac{{|calculated \ answer - correct \ answer|}}{{correct \ answer}} \times 100

Acids, Bases, and Solutions

• Strong acids and strong bases ionize completely in aqueous solution. This means they dissociate fully into ions.

• Strong Acids: HCl, HBr, HI, HNO3, H2SO4, and HClO4. Memorizing these is crucial for identifying strong acids.

• Strong Bases: Group 1 and 2 hydroxides (e.g., NaOH, KOH, Ca(OH)_2). Note that Group 2 hydroxides are less soluble but still strong bases.

• Dilution Equation: M1V1 = M2V2. This equation is used to calculate the concentration or volume needed when diluting a solution.

• Titration Equation: MAVA = MBVB. This equation applies to titrations where the stoichiometry between the acid and base is 1:1.

• Titration Curves: At the half-equivalence point for a titration, the pH = pKa of a weak acid. This is useful for determining the pKa experimentally.

Thermodynamics

• \Delta H < 0: Exothermic process. Heat is released to the surroundings.

• \Delta H > 0: Endothermic process. Heat is absorbed from the surroundings.

• \Delta G < 0: Thermodynamically-favored process (spontaneous). The reaction will proceed without external input of energy.

• \Delta G > 0: Non thermodynamically-favored process (non-spontaneous). The reaction requires an external input of energy to proceed.

Thermodynamics - Temperature Dependence:

• \Delta H: Negative, \Delta S: Positive => Thermodynamically Favored at All temperatures

• \Delta H: Positive, \Delta S: Negative => Never Thermodynamically Favored

• \Delta H: Positive, \Delta S: Positive => Thermodynamically Favored at Higher temperatures. At high temperatures, the T\Delta S term dominates.

• \Delta H: Negative, \Delta S: Negative => Thermodynamically Favored at Lower temperatures. At low temperatures, the \Delta H term dominates.

Galvanic Cells

• Galvanic cells (also known as voltaic cells) are electrochemical cells that generate electricity through spontaneous redox reactions.

• RED CAT and AN OX: Reduction at the cathode, oxidation at the anode

• OIL RIG: Oxidation is losing, reduction is gaining electrons

• The CAT gets FAT: Metallic cathodes increase in mass as metal ions are reduced and deposited onto the cathode.

• A/C: Electrons move through