Chem Covalent Bonding Sem 2 Key

Chemistry Final Exam Review Guide Covalent Bonding Explain why atoms bond. STABILITY - to achieve a complete octet (8 electrons in their outer shell) Describe the differences between an ionic bond and a covalent bond. Ionic bond: transfer of electrons between a metal and a nonmetal Covalent bond: sharing of electrons between 2 nonmetals Explain the difference between single, double, and triple covalent bonds including electrons shared, bond length, bond strength, AND bond dissociation energy (BDE). Single: 1 shares 2e-, longest, weakest, lowest BDE Double: shares 4e-, shorter, stronger, higher BDE Triple: shares 6e-, shortest, strongest, highest BDE   Compare the properties of ionic, covalent, and metallic substances. Property Ionic Metallic Covalent (metal + nonmetal) (metal) (2 nonmetals) State of Matter Solid Solid Liquid or gas Strength Hard, brittle Soft to hard, malleable, ductile Fairly soft Melting & Boiling Point High Low to very high Low to moderately high Conductivity Poor as a solid, good in aqueous solution Excellent Poor 5. Write the prefix corresponding to each number of atoms for naming covalent compounds. 1: mono 2: di 3: tri 4: tetra 5: penta 6: hexa 7: hepta 8: octa 9: nona 10: deca 6. Complete the table below Formula Name Formula Name CO2 carbon dioxide P2O5 Diphosphorus pentoxide IF3 iodine trifluoride ClO2 Chlorine dioxide P4O6 tetraphosphorus SiF4 Silicon tetrafluoride hexoxide SiI4 silicon tetraiodide B2I6 Boron triiodide N2O5 dinitrogen B6Si Hexaboron monosilicide pentoxide S2F10 disulfur decafluoride CO Carbon monoxide 7. Describe how one would determine the polarity of a bond. Obtain the electronegativity values for each atom and subtract. If EN difference is   < 0.5 nonpolar covalent, 0.5-1.7 polar covalent, >1.7 ionic 8. Explain how to decide if a molecule is polar or nonpolar. Molecular symmetry: if the molecule is symmetrical, it is nonpolar; if it is not symmetrical, then polar 9. For each molecule, draw the Lewis structure, determine the VSEPR shape, bond polarity using the electronegativity values from your notes (nonpolar covalent, polar covalent, or ionic), and molecular polarity.   SO2: O=S=O | O VSEPR shape: Bent (nonlinear) Bond Polarity: 3.5 - 2.4 = 1.1 PC Molecular Polarity: Polar H2O: H-O-H VSEPR shape: Bent (nonlinear) Bond Polarity: 3.5 - 2.2 = 1.3 PC Molecular Polarity: Polar 59. Calculate the hydrogen ion concentration of a glass of milk with a pH of 6.5. [H⁺] = antilog(-pH) = 10^(-6.5) = 3.2 x 10^(-7) 60. The concentration of H₃PO₄ is 3.0 x 10⁻⁴ moles/liter. What is the pH of the phosphoric acid solution? H₃PO₄ → 3H⁺ + PO₄³⁻ [H⁺] = 3(3 x 10⁻⁴) = 9 x 10⁻⁴ pH = -log(9 x 10⁻⁴) = 3.05 61. Complete the table below. | [H⁺] | [OH⁻] | pH | pOH | |---|---|---|---| | 3.2 x 10⁻³ | 3.2 x 10⁻¹² | 2.5 | 11.5 | | 1.2 x 10⁻⁹ | 7.9 x 10⁻⁶ | 8.9 | 5.1 | 62. How do sulfur oxides like SO₃ and nitrogen oxides like NO₂ contribute to acid rain? SO₃ and NO₂ produced by burning fossil fuels combine with water vapor in the atmosphere to produce acid precipitation. 63. Explain why lakes with limestone or calcium carbonate experience less adverse effects from acid rain than lakes with granite beds. The CaCO₃ in the limestone neutralizes the acid rain. **Redox Reactions** 64. Reactions that involve electron transfer are known as oxidation/reduction (or "redox") reactions. 65. What are the oxidation numbers (states) for the following elements? H is usually +1 O is usually -2 F is -1 group 1 elements +1 group 2 elements +2 66. Determine the oxidation numbers for the bolded atom. a. HNO₃ +5 b. NO₃⁻ +5 c. Cr₂O₃ +3 d. CaO +2 e. H₂SO₄ +6 67. Balance half-reactions and describe each as an oxidation or a reduction. a. Fe(s) + Ag+(aq) → Fe²+(aq) + Ag(s) Oxidation half rxn: Fe → Fe²⁺ + 2e⁻ Reduction half rxn: Ag⁺ + e⁻ → Ag (x2) → 2Ag⁺ + 2e⁻ → 2Ag Balanced overall rxn: Fe + 2Ag⁺ → Fe²⁺ + 2Ag b. 3Br₂ + 2Ga → 2GaBr₃ Oxidation half rxn: 2Ga → 2Ga³⁺ + 6e⁻ Reduction half rxn: 3Br₂ + 6e⁻ → 6Br⁻ Balanced overall rxn: 2Ga + 3Br₂ → 2Ga³⁺ + 6Br⁻ c. Mn²⁺(aq) + 2Br⁻(aq) → Br₂(l) + Mn(s) Oxidation half rxn: 2Br⁻ → Br₂ + 2e⁻ Reduction half rxn: Mn²⁺ + 2e⁻ → Mn Balanced overall rxn: 2Br⁻ + Mn²⁺ → Br₂ + Mn 68. Identify the oxidizing and reducing agents for the reactions from #5. a. Oxidizing agent: Ag⁺ Reducing Agent: Fe b. Oxidizing agent: Br₂ Reducing Agent: Ga c. Oxidizing agent: Mn²⁺ Reducing Agent: Br⁻