Name Date Class MOLECULAR COMPOUNDS. Distinguish molecular compounds from ionic compounds Identify the information a molecular formula provides

Transcription

1 8.1 MOLECULAR COMPOUNDS Section Review Objectives Distinguish molecular compounds from ionic compounds Identify the information a molecular formula provides Vocabulary covalent bond molecule diatomic molecule molecular compound molecular formula Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. Every substance is either an element or a(n) A compound is either 2 or ionic in nature. Most molecular 2. compounds are composed of two or more 3. Molecules 3. consisting of two atoms are 4 molecules. The chemical 4. formula of a molecular compound is a 5. Molecular 5. compounds tend to have 6 melting and boiling points, while 6. ionic compounds tend to have 7 melting and boiling points. 7. A molecular formula shows how many 8 of each 8. element a molecule contains, but it does not indicate the 9. 9 of the molecule. Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 10. A diatomic molecule contains two or three atoms. 11. Molecular compounds have relatively high boiling points. Chapter 8 Covalent Bonding 181

2 12. The molecular structure of carbon dioxide is one carbon atom with two oxygen atoms on opposite sides of it. 13. Covalent bonds exist when combining atoms give up or accept electrons. 14. A molecule contains two atoms. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B molecule molecular compound covalent bond diatomic molecule molecular formula a. compound composed of molecules b. a molecule consisting of two atoms c. shows the kinds and numbers present in a molecule of a compound d. joins atoms held together by sharing electrons e. an electrically neutral group of atoms joined together by covalent bonds Part D Questions and Problems Answer the following in the space provided. 20. A compound has a boiling point of 40 C. Is this compound most likely an ionic or a molecular compound? 21. Identify the number and kinds of atoms present in a molecule of each compound. a. butane (C 4 10 ) b. fluorobenzene (C 6 5 F) 22. Classify each particle as an atom or a molecule. a. C 4 d. e b. Ne e. CO 2 c. O Core Teaching Resources

3 8.2 TE NATURE OF COVALENT BONDING Section Review Objectives State a rule that usually tells how many electrons are shared to form a covalent bond Describe how electron dot formulas are used Predict when two atoms are likely to be joined by a double or a triple covalent bond Distinguish between a single covalent bond and other covalent bonds Describe how the strength of a covalent bond is related to its bond dissociation energy Describe how resonance structures explain bonding Identify some exceptions to the octet rule Vocabulary single covalent bond structural formulas unshared pairs double covalent bonds triple covalent bonds coordinate covalent bond polyatomic ion bond dissociation energy resonance structures Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. When atoms share electrons to gain the 1 configuration 1. of a noble gas, the bonds formed are 2. A 3 pair of 2. valence electrons constitutes a 4 covalent bond. Pairs of 3. valence electrons that are not shared between atoms are called Sometimes two or three pairs of electrons may be shared 5. to give 6 covalent bonds. In some cases, only one of the 6. atoms in a bond provides the pair of bonding electrons; this is a is required to break covalent bonds between 8. atoms. The total energy required to break the bond between two 9. covalently bonded atoms is known as the When it is possible to write two or more valid electron dot formulas for a molecule or ion, each formula is referred to as a 10. Chapter 8 Covalent Bonding 183

4 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 11. The modern interpretation of resonance is that electron pairs rapidly flip back and forth between the various electron dot structures. 12. The compound N 3 contains two double covalent bonds. 13. The chemical formulas of molecular compounds show the number and type of atoms in each molecule. 14. A molecule of bromine has six unshared pairs of electrons. 15. Carbon forms four single covalent bonds with other atoms. 16. A bond in which one atom contributes both bonding electrons is called a polyatomic covalent bond. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 17. single covalent bond 18. structural formula a. a chemical formula that shows the arrangement of atoms in a molecule or a polyatomic ion b. the amount of energy required to break a covalent bond between atoms 19. bond dissociation energy 20. polyatomic ion 21. coordinate covalent bond Part D Questions and Problems Answer the following in the space provided. 22. Draw electron dot structures for each of the following compounds a. Br 2 b. CN c. a tightly bound group of atoms that has a positive or negative charge and behaves as a unit d. a covalent bond in which one atom contributes both bonding electrons e. a chemical bond in which only one pair of electrons is shared by two bonded atoms c. N Core Teaching Resources

5 8.3 BONDING TEORIES Section Review Objectives Identify the difference between atomic and molecular orbits Describe how VSEPR theory helps predict the shapes of molecules Identify the ways in which orbital hybridization is useful in describing molecules Vocabulary molecular orbitals bonding orbital sigma bond pi bond tetrahedral angle VSEPR theory hybridization Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. The quantum mechanical model of bonding assumes that 1. atomic orbitals overlap to produce 1. A molecular orbit that 2. can be occupied by two electrons of a covalent bond is called a 3. 2, whose energy is 3 than that of the atomic orbitals 4. from which it formed. When two atomic orbitals combine to form 5. a molecular orbital that is symmetrical around the axis connecting 6. two atomic nuclei, a 4 bond is formed. When atomic 7. orbitals overlap side by side, they produce 5 bonds. 8. Electron dot structures fail to reflect the 6 shapes of molecules. 7 states that because electron pairs repel, molecular shape adjusts so the valence-electron pairs are as far apart as possible. Another way to describe molecules that provides information about both molecular bonding and molecular shape is 8. Chapter 8 Covalent Bonding 185

6 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 9. Unshared pairs of electrons affect the shape of molecules. 10. Molecular orbitals involve pi bonding. 11. A bonding orbital is a molecular orbital whose energy is higher than that of the atomic orbitals from which it is formed. 12. With hybridization, several atomic orbitals overlap to form the same total number of equivalent hybrid orbitals. 13. Sigma and pi bonds are found in the same molecule. 14. The methane molecule has four orbitals with tetrahedral angles of Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 15. sigma bond 16. pi bond a. states that because electron pairs repel, molecules adjust their shapes so that valence-electron pairs are as far apart as possible b. a process in which several atomic orbitals overlap to form the same number of equivalent hybrid orbitals 17. VSEPR theory 18. hybridization 19. linear molecule Part D Questions and Problems c. a term used to describe the shape of certain molecules such as CO 2 d. a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical along the axis connecting the two atomic nuclei e. a bond in which the bonding electrons are most likely to be found in the sausage-shaped regions above and below the nuclei of the bonded atoms Answer the following in the space provided. 20. Indicate the hybrid orbitals used by each carbon atom in the following compound. 3 C 2 C 3 C 2 C 4 C 2 C Core Teaching Resources

7 8.4 POLAR BONDS AND MOLECULES Section Review Objectives Describe how electronegativity values determine the charge distribution in a polar bond Describe what happens to polar molecules when placed between oppositely charged metal plates Distinguish intermolecular attractions from ionic bonds and from covalent bonds Identify the reason network solids have high melting points or decompose without melting Vocabulary nonpolar covalent bond polar covalent bond polar bond polar molecule dipole van der Waals forces dipole interactions dispersion forces hydrogen bonds network solids Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. When like atoms are joined by a covalent bond, the bonding 1. electrons are shared 1, and the bond is 2. When the 2. atoms in a bond are not the same, the bonding electrons are shared 3. 3, and the bond is 4. The degree of polarity of a bond 4. between any two atoms is determined by consulting a table of The attractions between opposite poles of polar molecules 6. are called 6. Another strong intermolecular attractive force 7. is the 7, in which a hydrogen covalently bonded to a very 8. 8 atom, such as 9, is also weakly bonded to an 9. unshared electron pair of another electronegative atom. Chapter 8 Covalent Bonding 187

8 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 10. In a polar covalent bond, the more electronegative atom has a slight positive charge. 11. In general, the electronegativity values of nonmetallic elements are greater than the electronegativity values of metallic elements. 12. A molecule with polar bonds is dipolar. 13. Covalent compounds are network solids. 14. If the electronegativity difference between two atoms is greater than 2.0, they will form an ionic bond. 15. Dispersion forces are weaker than hydrogen bonds. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 16. nonpolar covalent bond 17. polar covalent bond 18. polar molecule 19. van der Waals forces 20. network solid a. a substance in which all of the atoms are covalently bonded to each other b. a bond formed when the atoms in a molecule are alike and the bonding electrons are shared equally c. a term used to describe the weakest intermolecular attractions; these include dispersion forces and dipole interactions d. a bond formed when two different atoms are joined by a covalent bond and the bonding electrons are shared unequally e. a molecule in which one end is slightly positive and the other end is slightly negative 188 Core Teaching Resources

9 Part D Questions and Problems Answer the following in the space provided. 21. Arrange the following intermolecular attractions in order of increasing strength: dipole interactions, dispersion forces, and hydrogen bonds. 22. State whether the following compounds contain polar covalent bonds, nonpolar covalent bonds, or ionic bonds, based on their electronegativities. a. KF a. b. SO 2 b. c. NO 2 c. d. Cl 2 d. Chapter 8 Covalent Bonding 189

10 8 COVALENT BONDING Practice Problems In your notebook, solve the following problems. SECTION 8.1 MOLECULAR COMPOUNDS 1. Classify each of the following as an atom or a molecule. a. Be c. N 2 e. Ne b. CO 2 d. 2 O 2. Which of the following are diatomic molecules? a. CO 2 c. O 2 e. CO b. N 2 d. 2 O 3. What types of elements tend to combine to form molecular compounds? 4. What information does a molecule s molecular structure give? 5. ow do ionic compounds and molecular compounds differ in their relative melting and boiling points? SECTION 8.2 TE NATURE OF COVALENT BONDING 1. Draw the electron dot structure for hydrogen fluoride, F. 2. Draw the electron dot structure for phosphorus trifluoride, PF Draw the electron dot structure for nitrogen trichloride, NCl Draw the electron dot configuration for acetylene, C ow many resonance structures can be drawn for CO 2 3? Show the electron dot structures for each. SECTION 8.3 BONDING TEORIES 1. Predict the shape and bond angle for the compound carbon tetrafluoride, CF Predict the shape and bond angle for phosphorus trifluoride, PF Predict the type of hybridized orbitals involved in the compound boron trichloride, BCl What types of hybrid orbitals are involved in the bonding of the silicon atoms in silicon tetrafluoride, SiF 4? 5. Predict the shape and bond angle of fluorine monoxide, F 2 O. 190 Core Teaching Resources

11 6. Predict the shape of the C 2 CF 2 molecule. What hybridization is involved in the carbon-carbon bonds? 7. ow many sigma and pi bonds are used by each of the carbon atoms in the following compound? O C 1 C 2 O SECTION 8.4 POLAR BONDS AND MOLECULES 1. What type of bond nonpolar covalent, polar covalent, or ionic will form between each pair of atoms? a. Na and O b. O and O c. P and O 2. Explain why most chemical bonds would be classified as either polar covalent or ionic. 3. Would you expect carbon monoxide and carbon dioxide to be polar or nonpolar molecules? 4. Draw the structural formulas for each molecule and identify polar covalent bonds by assigning the slightly positive ( ) and slightly negative ( ) symbols to the appropriate atoms. a. N 3 b. CF 3 5. Which would you expect to have the higher melting point, CaO or CS 2? Chapter 8 Covalent Bonding 191

12 8 INTERPRETING GRAPICS Use with Section 8.3 Linear triatomic Trigonal planar Bent triatomic Pyramidal Tetrahedral Trigonal bipyramidal Figure 1 Common Molecular Shapes Use what you have learned in Chapter 8 to complete the table on the following page. Table 1 Arrangement of electron pairs about an atom Number of valence electron pairs about the central atom Arrangement of valence-electron pairs 2 linear 3 trigonal planar 4 tetrahedral 5 trigonal bipyramidal 192 Core Teaching Resources

13 Table 2 Molecular Geometries Molecule Electron Dot Structure Shape Bond Angle Resonance Structures 1. CO 2 2. C 4 3. SO 3 4. BeF 2 5. PF 3 6. PCl O 8. If you have access to a molecular model set, construct three-dimensional models of each of the molecules in the table. Compare your models to the shapes shown in Figure 1. With a protractor, measure all the bond angles in your models. Compare these angles to those predicted by VSEPR theory and label each of the illustrations in Figure 1 with the correct bond angles. Chapter 8 Covalent Bonding 193

14 8 COVALENT BONDING Vocabulary Review Select the term from the following list that best matches each description. polyatomic ion VSEPR theory bonding molecular orbital coordinate covalent bond sigma bond van der Waals forces hybridization molecule bond dissociation energy hydrogen bond 1. a bond in which one atom contributes both bonding electrons to a covalent bond 2. the total energy required to break the bond between two covalently bonded atoms 3. a molecular orbital whose energy is lower than that of the atomic orbitals from which it is formed 4. molecular orbital that lies along the axis connecting two atomic nuclei 5. states that because electron pairs repel, molecules adjust their shapes so that valence-electron pairs are as far apart as possible 6. a process in which several atomic orbitals mix to form the same number of equivalent hybrid orbitals 7. a tightly bound group of atoms that behaves as a unit and carries a charge 8. a term that collectively refers to dispersion forces and dipole interactions 9. a relatively strong intermolecular attraction in which a hydrogen that is covalently bonded to a very electronegative atom is also weakly bonded to an unshared pair of electrons of another electronegative atom 10. a tightly connected group of two or more atoms of nonmetallic elements that behave as an electrically neutral unit 194 Core Teaching Resources

15 8 COVALENT BONDING Chapter Quiz Choose the best answer and write its letter on the line. 1. A bond in which each atom contributes two electrons is 8.2 a. a double covalent bond. c. a polar covalent bond. b. an ionic bond. d. a coordinate covalent bond. 2. The electron dot structure for hydrogen sulfide, 2 S, is 8.2 a. S c. S b. S d. S 3. Which electron dot structure represents a nonpolar molecule? 8.2 a. O c. Cl b. Cl Cl d. C C F 4. Bond dissociation energy 8.2 a. is the energy required to break a single bond. b. of a C 2 bond is high. c. of a C 2 C bond is high. d. all of the above 5. A covalent bond formed between two elements that have an 8.4 electronegativity difference of 1.6 would be a. a nonpolar bond. c. a moderately polar bond. b. a very polar bond. d. an ionic bond. 6. You would expect a bond formed between a silicon atom and an 8.4 oxygen atom to be a. an ionic bond. c. a polar covalent bond. b. a coordinate covalent bond. d. a nonpolar covalent bond. Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 7. Molecular orbitals involve pi bonding An antibonding orbital is a molecular orbital whose energy is lower 8.3 than that of the atomic orbitals from which it is formed. 9. A three-atom molecule is bent Sigma and pi bonds are found in the same molecule A molecule contains two atoms. 8.1 Chapter 8 Covalent Bonding 195

16 8 COVALENT BONDING Chapter Test A A. Matching Match each description in Column B with the correct term in Column A. Write the letter of the correct description on the line. Column A Column B 1. coordinate covalent bond a. shows the kinds and numbers present in a molecule of a compound 2. nonpolar covalent bond b. chemical formula that shows the arrangement of atoms in molecules and polyatomic ions 3. hydrogen bond c. a covalent bond between two atoms of different electronegativities in which the bonding electrons are not shared equally 4. double covalent bond d. interaction caused by the motion of electrons 5. dispersion force e. a covalent bond formed by the equal sharing of bonding electrons by two atoms molecular formula structural formula polar bond triple covalent bond network solid f. a covalent bond involving two pairs of electrons; each atom donates one pair of electrons to the bond g. a covalent bond in which three pairs of electrons are shared by two bonded atoms h. substance in which all of the atoms are covalently bonded to each other i. a covalent bond between two atoms in which the shared electron pair comes from only one of the atoms j. force that occurs when a hydrogen atom that is covalently bonded to a very electronegative atom is also weakly bonded to an unshared pair of electrons in the same or a nearby molecule 196 Core Teaching Resources

17 B. Multiple Choice Choose the best answer and write its letter on the line. 11. Which of these elements does not exist as a diatomic molecule? a. I c. b. F d. e 12. Which one of the following compounds is not covalent? a. SCl 2 c. Cl b. KCl d. S 2 Cl ow many valence electrons does an atom of any halogen have? a. 1 c. 4 b. 2 d A diatomic molecule with a triple covalent bond is a. N 2. c. 2. b. Br 2. d. O A molecule of nitrous oxide, N 2 O, N 4 N y O contains all of the following except a. a coordinate covalent bond. c. a double bond. b. a triple bond. d. nonbonding pairs of electrons. 16. If a bonding pair of electrons is unequally shared between two atoms, the bond is a. ionic. c. coordinate covalent. b. nonpolar covalent. d. polar covalent. 17. What is the electron dot structure for water? a. 6 6 O 6 6 c. b. O d. 18. Which of the following compounds is not ionic? a. NaI c. CO 2 b. CaCl 2 d. Na 2 O 19. A covalent bond forms a. when an element becomes a noble gas. b. when atoms share electrons. c. between metals and nonmetals. d. when electrons are transferred from one atom to another. 20. What is the electron dot structure for the polyatomic ion O? a. [ O ] c. [ O] b. [ O ] d. O O [ O ] 21. Which of these compounds would not have covalent bonds? a. NO 2 c. N 2 O 4 b. K 2 O d. 2 O 2 Chapter 8 Covalent Bonding 197

18 22. A molecule with a single covalent bond is a. CO 2. c. NO. b. F 2. d. N Chlorine is a gas, bromine is a liquid, and iodine is a solid because of differences in the strength of their a. hydrogen bonds. c. dipole interactions. b. dispersion forces. d. polar bonds. 24. When forms a bond with 2 O to form hydronium ion, 3 O, this bond is called a coordinate covalent bond because a. both bonding electrons come from the oxygen atom. b. it is an especially strong bond. c. the electrons are equally shared. d. the oxygen no longer has eight electrons surrounding it. 25. Which of the following molecules has one lone pair of electrons? a. C 4 c. 2 O b. Cl d. N Which of the following is the weakest? a. hydrogen bond c. dipole interaction b. polar covalent bond d. ionic bond 27. The carbon tetrachloride molecule is a. four-cornered. c. tetrahedral. b. square. d. pyramidal. C. Questions Answer the following questions in the space provided. 28. Draw structural formulas for the following substances. a. Br 2 b. N 2 c. CO 29. State whether the following compounds contain polar covalent bonds, nonpolar covalent bonds, or ionic bonds. (You may refer to the table of electronegativities on the top of the next page.) a. KF b. SO 2 c. NO 2 d. Br 198 Core Teaching Resources

19 Reference Section Electronegativities 1A A 3A 4A 5A 6A 7A Li 1.0 Na 0.9 K 0.8 Be 1.5 Mg 1.2 Ca 1.0 B 2.0 Al 1.5 Ga 1.6 C 2.5 Si 1.8 Ge 1.8 N 3.0 P 2.1 As 2.0 O 3.5 S 2.5 Se 2.4 F 4.0 Cl 3.0 Br The following covalent molecules have only single covalent bonds. Draw an electron dot structure for each one. a. Br c. PCl 3 e Ne Ar Kr b. 2 O 2 D. Essay 31. Describe a network solid and give two examples. E. Additional Questions and Problems Answer the following in the space provided. Show your work. 32. Calculate the total energy needed to dissociate all the bonds in one mole of ethyl alcohol, C 2 5 O. (Assume that the total energy is the sum of the individual bond dissociation energies.) The structural formula of ethyl alcohol is Bond Energy (kj/mol) C C 2 O 356 O C 2 2 C 2 O 2 Chapter 8 Covalent Bonding 199

20 33. With the aid of a diagram, describe how the overlap of one 2p orbital from each of two atoms forms a sigma bond, but the overlap of the remaining two 2p orbitals from each atom forms pi bonds. 34. Indicate the hybrid orbitals used by each carbon atom in the following compound. The carbons are numbered for easy reference. 1 C 2 C 3 C 4 C 5 C O 35. Draw electron dot structures for PCl 5 and SF 6. (int: These compounds are exceptions to the octet rule.) 200 Core Teaching Resources

21 8 COVALENT BONDING Chapter Test B A. Matching Match each term in Column B with the correct description in Column A. Write the letter of the correct term on the line. Column A Column B 1. the mixing of several atomic orbitals to form the same number of equivalent hybrid orbitals a. molecular compound 2. two or more valid electron dot formulas that can be written for the same molecule b. VSEPR theory 3. a chemical formula that shows the arrangement of atoms in molecules and polyatomic ions c. van der Waals forces 4. the weakest attractions that exist between molecules d. single covalent bond 5. Because electron pairs repel, molecules adjust their shapes so that the valence-electron pairs are as far apart as possible. e. resonance structures a covalent bond in which one pair of electrons is shared between two atoms a molecule in which one end is slightly negative and the other end is slightly positive a covalent bond formed between two different atoms in which the bonding electrons are shared unequally an electrically neutral group of atoms joined together by covalent bonds a covalent bond in which one atom contributes both bonding electrons f. polar molecule g. hybridization h. structural formula i. polar covalent bond j. coordinate covalent bond Chapter 8 Covalent Bonding 201

22 B. Multiple Choice Choose the best answer and write its letter on the line. 11. Which of the following exists as a diatomic molecule? a. e c. Cl b. Ar d. Na 12. The diatomic molecule among the following that contains a single covalent bond is a. F 2. c. N 2. b. O 2. d. O Atoms share electrons in order to acquire the electron configurations of a. alkali metals. c. halogens. b. alkaline earth metals. d. noble gases. 14. In Cl 2, what is the total number of unshared pairs of electrons? a. 1 c. 4 b. 2 d The diatomic molecule among the following that contains a triple covalent bond is a. O 2. c. 2. b. Cl 2. d. N In the N 2 molecule, what is the number of unshared pairs of electrons in each nitrogen atom? a. 1 c. 3 b. 2 d The covalent molecule among the following is a. NaCl. c. CaO. b. N 3. d. KF. 18. ow many single covalent bonds are there in a molecule of C 4? a. 1 c. 3 b. 2 d ow many double covalent bonds are there in a molecule of CO 2? a. 1 c. 3 b. 2 d The molecule among the following that contains only one single covalent bond is a. N 3. c. I. b. N 2. d. 2 O. 21. In forming the molecule F, the F atom attains the electron configuration of a. e. c. Ar. b. Ne. d.. Cl. 202 Core Teaching Resources

23 22. Which molecule among the following contains a coordinate covalent bond? a. CO c. 2 O b. N 3 d. CCl The molecule among the following that exhibits resonance structures is a. CO 2. c. O 3 (ozone). b. C 4. d. N Resonance structures can be considered a. polar molecules. c. coordinate covalent molecules. b. hybrids. d. none of the above 25. Substances that show relatively strong attractions to an external magnetic field are said to be a. diamagnetic. c. nonmagnetic. b. paramagnetic. d. none of the above 26. Oxygen is an example of a substance that is a. diamagnetic. c. nonmagnetic. b. paramagnetic. d. none of the above 27. When two atomic orbitals combine to form a molecular orbital that is symmetrical along the axis connecting the two atomic nuclei, the bond that is produced is referred to as a(n) a. ionic bond. c. sigma bond. b. pi bond. d. none of the above 28. The shape of a molecule of N 3 is said to be a. tetrahedral. c. bent. b. pyramidal. d. linear. 29. In a methane (C 4 ) molecule, the mixing of one 2s orbital with three 2p orbitals forms a. one sp 4 hybrid orbital. c. one sp 3 hybrid orbital. b. four sp hybrid orbitals. d. four sp 3 hybrid orbitals. 30. The overlap of atomic s orbitals produces a(n) a. ionic bond. c. sigma bond. b. pi bond. d. none of the above 31. Which of the following contains a polar covalent bond? a. O 2 c. CaO b. MgCl 2 d. F 32. What type of bond would be expected in a molecule of LiF? a. ionic bond c. nonpolar covalent bond b. polar covalent bond d. none of the above Chapter 8 Covalent Bonding 203

24 33. Among the following molecules, the one containing the most polar bond is a. F. c. Br. b. Cl. d. 2 O. 34. The polar molecule among the following is a. CCl 4. c. 2 O. b. CO 2. d. N The strongest intermolecular attractive forces from among those listed are a. dispersion forces. c. hydrogen bonds. b. dipole interactions. d. cannot be determined 36. The melting and boiling points of most molecular compounds are a. lower than those of most ionic compounds. b. about the same as those of most ionic compounds. c. higher than those of most ionic compounds. d. sometimes higher and sometimes lower than those of most ionic compounds. 37. Network solids a. have low melting points. c. are extremely hard. b. have low boiling points. d. are generally ductile. C. Questions Answer the following in the space provided. 38. Write both the electron dot structure and the structural formula for each of the following covalent molecules: a. 2 b. N 2 c. 2 O d. N 3 e. CO Electron Dot Structure Structural Formula 204 Core Teaching Resources

25 39. Write the electron dot formula for each of the following polyatomic ions. a. N 4 b. PO 4 3 D. Essay 40. Distinguish between ionic and covalent bonds in terms of how each is formed and how to predict which will be formed when various elements combine. Chapter 8 Covalent Bonding 205

26 E. Additional Questions and Problems Answer the following in the space provided. Show your work. 41. Use the electronegativity table below to determine the type of bond (polar covalent, nonpolar covalent, or ionic) that would be formed between each of the following elements. Give the electronegativity difference in each case. Reference Section Electronegativities 1A A 3A 4A 5A 6A 7A Li 1.0 Na 0.9 K 0.8 Be 1.5 Mg 1.2 Ca 1.0 B 2.0 Al 1.5 Ga 1.6 C 2.5 Si 1.8 Ge 1.8 N 3.0 P 2.1 As 2.0 O 3.5 S 2.5 Se 2.4 F 4.0 Cl 3.0 Br 2.8 e Ne Ar Kr Bond Type Electronegativity Difference a., Cl b., S c. S, Cl d. Na, F e. Cl, Br f. Al, Br 42. Given the following bond dissociation energy values, calculate the total energy that would be required to break all of the covalent bonds in 0.25 mol of ethane (C 2 6 ). C C = 347 kj/mol and C = 393 kj/mol 206 Core Teaching Resources