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$$$CH_4$$)

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

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

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

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

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

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

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

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

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

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

  • 4 atoms, 2 lone pairs: Square Planar, 90° (e.g., $XeF_4$$$XeF_4$$). 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$$$BeCl_2$$)

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

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

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^+$$$Na^+$$, $K^+$$$K^+$$, or $NH_4^+$$$NH_4^+$$ ions is soluble in water. These ions generally form soluble salts.

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

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

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

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

• Sulfides ($S^{2-}$$$S^{2-}$$), carbonates ($$CO3^{2-}$), phosphates ($$$), phosphates ($$PO4^{3-}$), and chromates ($$$), and chromates ($$CrO4^{2-}$) are generally insoluble, except with Group 1 cations and$$$) 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: $$\Delta H = \Sigma H{\text{bonds broken}} – \Sigma H{\text{bonds formed}}$(LEFT SIDE – RIGHT SIDE). Breaking bonds requires energy (endothermic, positive$$$ (LEFT SIDE – RIGHT SIDE). Breaking bonds requires energy (endothermic, positive $$H$), and forming bonds releases energy (exothermic, negative$$$), and forming bonds releases energy (exothermic, negative $$H$$).

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

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$$$Ca(OH)_2$$). 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$$$\Delta H < 0$$: Exothermic process. Heat is released to the surroundings.

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

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

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

Thermodynamics - Temperature Dependence:

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

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

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

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