Chem Test PDF

# Introduction to Chemical Bonding ## Ava Coury Answer the following questions in complete sentences. 1. What is a chemical bond? A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. 2. In general, what deter...

# Introduction to Chemical Bonding ## Ava Coury Answer the following questions in complete sentences. 1. What is a chemical bond? A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. 2. In general, what determines whether atoms will form chemical bonds? The number of valence electrons. 3. What is a molecule? A molecule is a group of two or more atoms that form the smallest identifiable unit. 4. Make a three-column list to distinguish between ionic, polar-covalent and nonpolar-covalent bonds. | **Ionic** | **PC** | **NC** | |---|---|---| | Metal and nonmetal transfer electrons | Electrons are not shared equally, because one atom attracts the shared electrons more than the other determined by electronegativity differences | Electrons are shared equally | 5. What determines bond length? The number of bonded electrons; the higher the order, the stronger the pull. 6. In general, how are bond energies and bond lengths related? The lower the bond length, the higher the bond energy is. 7. Use the data in the tables below to arrange the bonds listed in order of increasing bond length, from shortest bond to longest. | Bond | Bond Energy (kJ/mol) | |---|---| | H-F | 569 | | H-I | 299 | | H-Cl | 432 | | H-Br | 366 | H-F, H-Cl, H-Br, H-I 8. Use the data in the tables below to arrange the bonds listed in order of increasing bond length, from shortest bond to longest. | Bond | Bond Energy (kJ/mol) | |---|---| | C-C | 346 | | C=C | 835 | | C≡C | 612 | C-C, C=C, C≡C 9. As applied to covalent bonding, what is meant by an unshared or lone pair of electrons? It is a pair of valence electrons that are not shared with another atom in a covalent bond. 10. What is the relationship between electronegativity and the covalent character of a chemical bond? The greater the difference in electronegativity, the more polarized the electron distribution and the larger the partial charges of the atoms. 11. Determine the electronegativity difference, the probable bond type, and the more electronegative atom between the following pairs of atoms. | Elements Bonded | Electronegativity Difference | Bond Type | More Negative Atom | |---|---|---|---| | Hydrogen & Oxygen | 1.4 | Polar | Oxygen | | Nitrogen & Hydrogen | 0.9 | Polar | Nitrogen | | Potassium & Fluorine | 3.2 | Ionic | Fluorine | | Silicon & Chlorine | 1.2 | Polar | Chlorine | | Oxygen & Chlorine | 0.5 | Polar | Oxygen | | Selenium & Sulfur | 0.1 | Nonpolar | Sulfur | | Carbon & Hydrogen | 0.4 | Polar | Carbon | 12. List the bonding pairs in problem 11 in order of increasing covalent character (least covalent to most covalent). K-F, H-O, Si-Cl, N-H, O-Cl, Se-S, C-H Complete each of the following sentences by filling in the appropriate word or phrase from the list below. * negative * positive * crisscross * noble gas * electrons * anion * cation * ions * electron configuration * polyatomic * empirical formula 13. An ionic bond is an attraction between oppositely charged **ions**. 14. Anions have a **negative** charge. 15. An atom becomes an ion by losing or gaining **electrons**. 16. The **octet** rule states that atoms tend to gain, lose or share electrons in order to acquire a full set of valence electrons. 17. The atoms that make up **cations** ions are bonded together by covalent bonds. If the statement is true, write "true." If it is false, change the underlined word or words to make it true. Write your answer on the line. 1. **False; losing** Calcium becomes a cation by gaining two electrons. 2. **True** A cation has a positive charge 3. **True** A great deal of energy is produced when an ionic compound is formed. 4. **False; covalent** A group of atom united by ionic bonds is called a molecule. 5. **True** A covalent bond is formed by a shared pair of electrons. 6. **True** A molecular formula tells you how many atoms are in a single molecule of the compound. 7. **False, Octet** The empirical formula for a molecule specifies which atoms are bonded to each other in the molecule. 8. **False; lone bonding pair** A pair of electrons not involved in bonding is called a shared electron pair. 9. **False; equally** In nonpolar covalent bonds, the electrons are shared unequally between two atoms. ## Covalent Bonding Target 4 HW I can name covalent compounds. ### Part One: Write the name for the following compounds. 1. P₃O₉: Triphosphorus nonaoxide 2. N₂O₅: Dinitrogen pentoxide 3. N₂I₄: Dinitrogen tetraiodine 4. CO: Carbon monoxide 5. S₃O₇: Trisulfur heptaoxide 6. H₃Cl₅: Trihydrogen pentachloride 7. Cl₃O₁₀: Trichlorine decasxide 8. NO₂: Nitrogen dioxide 9. As₂O₄: Diarsenic tetraoxide 10. CH₄: Carbon tetrahydride ### Part Two: Write the formulas for the following compounds. 11. Trinitrogen hexasulfide: N₃S₆ 12. Boron difluoride: BF₂ 13. Carbon trioxide: CO₃ 14. Tetrasilicon heptachloride: Si₄Cl₇ 15. Nonaphosphorus difluoride: P₉F₂ 16. Arsenic tribromide: AsBr₃ 17. Dihydrogen monoxide: H₂O 18. Tricarbon decafluoride: C₃F₁₀ 19. Octaphosphorus nonabromide: P₈Br₉ 20. Dicarbon octahydride: C₂H₈ # Lewis Structures Draw Lewis structures for each of the following molecules. 1. BCl₃: ``` :CI: :CI-B-CI: :CI: ``` 2. NH₃ (ammonia): ``` H / | \ H-N-H \ H ``` 3. SCN: ``` :S: || S-C=N: ``` 4. H₂CO: ``` H | O=C-H | H ``` 5. SO₃^2-: ``` :O: || :O-S-O: || :O: ``` # Resonance Structures Draw all possible Resonance Structures for each of the following molecules. 1. SCN: ``` [S=C=N] <=> [N=C=S] ``` 2. SO₃: ``` :Ö: :Ö: :O: || || || :O-S-O: <=> :O-S-O: <=> :O-S-O: || || || :Ö: :Ö: :Ö: ``` 3. CS₂: ``` :S=C=S: <=> :S=C=S: ``` 4. NO₃^-: ``` :Ö: :Ö: :Ö: / || \ / \ / \ :O-N=O: <=> :Ö-N-O: <=> :Ö-N-O: \ || / \ / \ / :Ö: :Ö: :Ö: ``` 5. NO₂^-: ``` [:O=N-O:] <=> [:Ö-N=O: ] ``` # VSEPR Theory Determine the VSEPR model and geometry for each of the following molecules. 1. CS₂: :S=C=S: **AB₂ - Linear - 180°** 2. NH₃ (ammonia): ``` H / | \ H-N-H \ H ``` **AB₃E Trigonal Pyramidal - 107°** 3. CCl₄: ``` Cl / | \ Cl-C-Cl \ Cl ``` **AB₄ - Tetrahedral - 109.5°** 4. BH₃: ``` H / | \ H-B-H \ H ``` **AB₃ - Trigonal Planar - 120°** 5. NO₃^-: ``` :Ö: / || \ :O-N=O: | || / | / :Ö: :Ö: ``` **AB₃ - Trigonal Planar - 120°** # Hybridization Theory Determine the hybridization, geometry, and bond angles for each of the following molecules. 1. SO₂: :Ö=S-Ö: **AB₂E - Bent Polar - Sp² - ∠ 120°** 2. NH₄⁺: ``` H / | \ H-N-H \ H ``` **AB₄ - Tetrahedral - Sp³ - 109.5°** 3. CCl₄: ``` Cl / | \ Cl-C-Cl \ Cl ``` **AB₄ - Tetrahedral - Sp³ - 109.5°** 4. COF₂: ``` F / | \ F-C-O | :Ö: ``` **AB₃E Trigonal Pyramidal - Sp³ - 107°** 5. NO₃^-: ``` :Ö: / || \ :O-N=O: | || / | / :Ö: :Ö: ``` **AB₃ Trigonal Planar - Sp² - 120°** # Intermolecular Forces Determine the most predominant type of intermolecular force present in the following molecules. 1. PCl₃: :Cl: :Cl-P-Cl: :Cl: **DD** 2. NH₃ (ammonia): ``` H / | \ H-N-H \ H ``` **H-bond** 3. CHCl₃: :Cl: :Cl-C-Cl: :Cl: H **DD** 4. H₂CO: ``` H / | H-C-O | H ``` **DD** 5. H₂S: ``` H / | \ H-S-H \ H ``` **DD** 6. OF₂: :F-O-F: **DD** # Boiling Points and Intermolecular Forces * A technician was cleaning up the laboratory when he discovered two steel gas cylinders. One cylinder was labeled Boiling Point: -188.1°C. The other was labeled Boiling Point: -34.05°C. Puzzled, the technician took the cylinders to his supervisor.* * "One cylinder contains gaseous F₂ and the other contains gaseous Cl₂," said his supervisor. She then asked the technician to label the two containers correctly. He asked, "But, which is which?" The supervisor responded indignantly that, to a chemist, the answer should be obvious! * Seeing the disgruntled look on the technician's face, she offered the following hints to help him solve the problem. See if you can solve the problem using the following steps.* **Hint: Boiling points are related to intermolecular attractive forces.** 1. a. List the three types of intermolecular forces. * Dispersion forces * Dipole-Dipole Forces * Hydrogen Forces b. Which one of these three forces is present in F₂ and Cl₂? * **Dispersion** **Hint: Molecular size affects the strength of intermolecular forces.** 2. Explain the effect that large molecular size has on the strength of intermolecular forces. *Because of the bigger electron cloud and more opportunities for temporary imbalances in the electron distribution* 3. Look at the periodic table. Can you decide which molecule is larger, F₂ or Cl₂? Explain your answer. * **Cl₂ is larger because chlorine is larger than fluorine.** **Hint: The strength of intermolecular attractive forces in a substance determines its boiling point.** 4. Do stronger intermolecular forces result in higher or lower boiling points? * **Higher** 5. Which substance, F₂ or Cl₂, has the stronger intermolecular forces? * **Cl₂** 6. a. What is the boiling point of F₂? * **-188.1°F** b. What is the boiling point of Cl₂? * **-34.05°F** # Polar Bonds *Draw arrows on each of the molecular structures below to identify the polar bonds. Then, use the diagrams to answer each of the following questions.* H | H-C-H | H-C-H | H-C-H | H **Propane** H | H-C-O-H | H-C-H | H-C-H | H **1-Propanol** H | H-C-H | H-C-O-H | H-C-H | H **2-Propanol** 1. Compare and contrast the structures of these three molecules. * Propane - Nonpolar * 1-Propanol - Polar * 2-Propanol - Polar 2. Which molecule would you predict to have the greatest polarity? Explain your answer. * **2-Propanol because the longest connection between molecules is located on the central atom.** 3. Suggest reasons why both 1-propanol and 2-propanol are liquids at room temperature while propane in a gas. Base your answer on the molecular structure of these 3 molecules. * **It is because of the oxygen atom that is located in the structure.** 4. Examine the boiling point for each molecule listed in the table below. Describe the relationship between polarity and boiling point. | Molecule | Boiling Point (°C) | |---|---| | Propane | -42.1 | | 1-propanol | 97.4 | | 2-propanol | 82.4 | * **Polar molecules have a higher melting point compared to a nonpolar molecule.** 5. Propose an explanation for the relationship you noted in question 4. * **Polar molecules have stronger bonds, meaning they need more energy to break the connection between them.**