covalent bond molecule sigma bond exothermic pi bond When sharing of electrons occurs, the attachment between atoms that results is called a(n) (1)

Transcription

1 STUDY GUIDE Covalent Bonding Section 8.1 The Covalent Bond In your textbook, read about the nature of covalent bonds. Use each of the terms below just once to complete the passage. covalent bond molecule sigma bond exothermic pi bond When sharing of electrons occurs, the attachment between atoms that results is called a(n) (1). When such an attachment is formed, bond dissociation energy is released, and the process is (2). When two or more atoms bond by means of electron sharing, the resulting particle is called a(n) (3). If the electrons shared are centered between the two atoms, the attachment is called a(n) (4). If the sharing involves the overlap of parallel orbitals, the attachment is called a(n) (5). In your textbook, read about single and multiple bonds and bond strength. Circle the letter of the choice that best completes the statement or answers the question. 6. In what form do elements such as hydrogen, nitrogen, and oxygen normally occur? a. as single atoms c. as molecules containing three atoms b. as molecules containing two atoms d. as molecules containing four atoms 7. How many electrons are shared in a double covalent bond? a. none b. one c. two d. four 8. Bond length is the distance between a. two molecules of the same substance. c. the nuclei of two attached atoms. b. the electrons in two attached atoms. d. the orbitals of two attached atoms. 9. Which of the following relationships relating to bond length is generally correct? a. the shorter the bond, the stronger the bond b. the shorter the bond, the weaker the bond c. the shorter the bond, the fewer the electrons in it d. the shorter the bond, the lower the bond dissociation energy 100 Chemistry: Matter and Change Chapter 8 Study Guide

2 STUDY GUIDE Section 8.2 Naming Molecules In your textbook, read about how binary compounds and acids are named from their formulas. For each statement below, write true or false. 1. Binary molecular compounds are generally composed of a metal and a nonmetal. 2. The second element in the formula of a binary compound is named using the suffix -ite. 3. The prefix tetra- indicates three atoms. 4. The prefix hexa- indicates six atoms. 5. In naming the first element in a formula, the prefix mono- is not used. 6. For binary acids, the hydrogen part of the compound is named using the prefix hydro-. 7. An oxyacid contains only two elements. 8. If the name of the anion of an oxyacid ends in -ate, the acid name contains the suffix -ous. In your textbook, read about naming molecular compounds and oxyacids. For each item in Column A, write the letter of the matching item in Column B. Column A Column B 9. CO 10. CO H 2 CO NH N 2 O HNO HNO HBr 17. HBrO 3 a. b. c. d. e. f. g. h. i. hydrobromic acid dinitrogen tetroxide carbon monoxide nitrous acid ammonia nitric acid carbonic acid bromic acid carbon dioxide Study Guide Chemistry: Matter and Change Chapter 8 101

3 STUDY GUIDE Section 8.3 Molecular Structures In your textbook, read about Lewis structures. For each statement below, write true or false. 1. A structural formula shows the arrangement of the atoms in a molecule. 2. The central atom in a molecule is the one with the highest electron affinity. 3. In molecules, hydrogen is always a terminal atom. 4. The number of bonding pairs in a molecule is equal to the number of electrons. 5. To find the total number of electrons available for bonding in a positive ion, you should add the ion charge to the total number of valence electrons of the atoms present. 6. The electrons in a coordinate covalent bond are donated by both the bonded atoms. 7. Resonance occurs when more than one valid Lewis structure can be written for a molecule. 8. Nitrate is an example of an ion that forms resonance structures. 9. The carbon dioxide molecule contains two double bonds. 10. All electrons in an atom are available for bonding. 11. In the sulfate ion (SO 4 2 ), 32 electrons are available for bonding. 12. When carbon and oxygen bond, the molecule contains ten pairs of bonding electrons. In your textbook, read about resonance structures and exceptions to the octet rule. For each item in Column A, write the letter of the matching item in Column B. Column A Column B 13. Odd number of valence electrons 14. Fewer than 8 electrons around an atom 15. More than 8 electrons around central atom 16. More than one valid Lewis structure a. O 3 b. BF 3 c. NO d. SF Chemistry: Matter and Change Chapter 8 Study Guide

4 STUDY GUIDE Section 8.4 Molecular Shape In your textbook, read about the VSEPR model. Circle the letter of the choice that best completes the statement. 1. The VSEPR model is used mainly to a. determine molecular shape. c. determine ionic charge. b. write resonance structures. d. measure intermolecular distances. 2. The bond angle is the angle between a. the sigma and pi bonds in a double bond. c. two terminal atoms and the central atom. b. the nucleus and the bonding electrons. d. the orbitals of a bonding atom. 3. The VSEPR model is based on the idea that a. there is always an octet of electrons around an atom in a molecule. b. electrons are attracted to the nucleus. c. molecules repel one another. d. shared and unshared electron pairs repel each other as much as possible. 4. The shape of a molecule whose central atom has four pairs of bonding electrons is a. tetrahedral. b. trigonal planar. c. trigonal pyramidal. d. linear. 5. The shape of a molecule that has two covalent single bonds and no lone pairs on the central atom is a. tetrahedral. b. trigonal planar. c. trigonal pyramidal. d. linear. 6. The shape of a molecule that has three single covalent bonds and one lone pair on the central atom is a. tetrahedral. b. trigonal planar. c. trigonal pyramidal. d. linear. In your textbook, read about ization. Use each of the terms below just once to complete the passage. carbon ization sp 3 identical methane The formation of new orbitals from a combination or rearrangement of valence electrons is called (7). The orbitals that are produced in this way are (8) to one another. An example of an element that commonly undergoes such formation is (9). When this atom combines its three p orbitals and its one s orbital, the orbitals that result are called (10) orbitals. An example of a molecule that has this type of orbital is (11). Study Guide Chemistry: Matter and Change Chapter 8 103

5 STUDY GUIDE Section 8.5 Electronegativity and Polarity In your textbook, read about electronegativity. Use the table of electronegativities below to answer the following questions. 1 H Li Na K Rb Cs Fr Be Mg Ca Sr Ba Ra Sc Y La Ac Ti Zr Hf V Nb Ta 1.5 Electronegativities of Some Elements 24 Cr Mo W Mn Tc Re 1.9 Metal Metalloid Nonmetal 26 Fe Ru Os Co Rh Ir Ni Pd Pt Cu Ag Au Zn Cd Hg B Al Ga In Tl C Si Ge Sn Pb N P As Sb Bi O S Se Te Po F Cl Br I At What is the meaning of the term electronegativity? 2. Which element has the highest electronegativity? What is the numerical value? What are the name and group number of the chemical family that has the highest overall electronegativities? 3. Which element has the lowest electronegativity? What is the numerical value? What are the name and group number of the chemical family that has the lowest overall electronegativities? 4. What general trend in electronegativity do you note going down a group? Across a period? 5. How are the electronegativity values used to determine the type of bond that exists between two atoms? In your textbook, read about the properties of covalent compounds. For each statement below, write true or false. 6. Ionic compounds are usually soluble in polar substances. 7. In a covalent molecular compound, the attraction between molecules tends to be strong. 104 Chemistry: Matter and Change Chapter 8 Study Guide

6 STUDY GUIDE Section 8.5 continued In your textbook, read about bond polarity. Using the table of electronegativities on the preceding page, circle the letter of the choice that best completes the statement or answers the question. 8. Unequal sharing of electrons between two bonded atoms always indicates a. a nonpolar covalent bond. c. a polar covalent bond. b. an ionic bond. d. a polar molecule. 9. When electronegativities of two bonded atoms differ greatly, the bond is a. polar covalent. b. coordinate covalent. c. polar covalent. d. ionic. 10. What is the electronegativity difference that usually is the dividing line between covalent and ionic bonds? a. 1.0 b. 1.7 c. 2.7 d The symbol is placed next to which of the following? a. the less electronegative atom in a polar covalent bond c. a positive ion b. the more electronegative atom in a polar covalent bond d. the nucleus 12. A nonpolar covalent bond is one in which a. electrons are transferred. c. electrons are shared equally. b. electrons are shared unequally. d. both electrons are provided by the same atom. 13. Molecules containing only polar covalent bonds a. are always polar. c. are always ionic. b. may or may not be polar. d. are always nonpolar. 14. What factor other than electronegativity determines whether a molecule as a whole is polar or not? a. temperature b. its geometry c. its physical state d. its mass 15. Which of the following correctly describes the compound water, H 2 O? a. ionic c. polar overall, with nonpolar covalent bonds b. nonpolar overall, with polar covalent bonds d. polar overall, with polar covalent bonds 16. Which of the following correctly describes the compound carbon tetrachloride, CCl 4? a. ionic c. polar overall, with nonpolar covalent bonds b. nonpolar overall, with polar covalent bonds d. polar overall, with polar covalent bonds 17. A molecule of ammonia, NH 3, is a. nonpolar because it is linear. b. polar because it is linear. c. nonpolar because there is no electronegativity difference. d. polar because there is an electronegativity difference and the molecule is trigonal pyramidal. Study Guide Chemistry: Matter and Change Chapter 8 105

7 CHAPTER ASSESSMENT Covalent Bonding Reviewing Vocabulary Match the definition in Column A with the term in Column B. Column A 1. The tendency of an atom in a compound to attract electrons 2. A kind of bond in which there is unequal sharing of electrons 3. Any bond in which there is electron sharing 4. The particle formed when two or more atoms bond covalently 5. Reactions that occur when more energy is released forming new bonds than is required to break bonds in the initial reactants Column B a. structural formula b. molecule c. VSEPR model d. coordinate covalent bond e. ization f. oxyacid g. electronegativity h. sigma bond 6. A kind of bond in which electrons are shared in an area centered between the two atoms 7. A kind of bond formed by overlap of parallel orbitals 8. Any acidic compound that contains oxygen 9. A model that shows how the atoms are arranged in a molecule 10. Reactions that occur when more energy is required to break existing bonds in reactants than is released when new bonds form in the product molecules 11. A condition that occurs when more than one valid Lewis structure can be drawn for a molecule 12. A kind of bond in which one of the atoms provides both electrons for sharing 13. A model used to determine molecular shape 14. The combining of orbitals in an atom to form new, identical orbitals i. polar covalent j. pi bond k. covalent bond l. resonance m. endothermic n. exothermic 106 Chemistry: Matter and Change Chapter 8 Chapter Assessment

8 CHAPTER ASSESSMENT Understanding Main Ideas (Part A) Circle the letter of the choice that best completes the statement or answers the question. 1. In the formation of a covalent bond, electrons are a. shared. b. lost. c. gained. d. transferred. 2. Which of the following elements normally exists in the form of diatomic molecules? a. helium b. argon c. iron d. nitrogen 3. Four electrons are shared in a a. single covalent bond. c. triple covalent bond. b. double covalent bond. d. quadruple covalent bond. 4. Which of the following molecules contains only sigma bonds? a. methane b. oxygen c. carbon dioxide d. nitrogen 5. Which of the following molecules contains a triple bond? a. methane b. oxygen c. carbon dioxide d. nitrogen 6. How many pi bonds are there in a triple bond? a. none b. one c. two d. three 7. Which of the following molecules would be expected to have the greatest bond dissociation energy? a. F 2 b. O 2 c. N 2 d. Cl 2 In the space at the left, write true if the statement is true; if the statement is false, change the italicized term to make it true. 8. In a chemical name, the prefix used to indicate the presence of two atoms of a given kind is bi-. 9. The prefix hydro- is used in naming binary acids. 10. The oxyacid suffix for an acid that contains an anion ending in -ate is -ic. 11. In Lewis structures, hydrogen is always a terminal atom. 12. In the carbon dioxide molecule, the central atom is a carbon atom. 13. In the compound BH 3, the boron atom has more than an octet of electrons. 14. The VSEPR model is based on the idea that in a molecule, nuclei repel each other as much as possible. Chapter Assessment Chemistry: Matter and Change Chapter 8 107

9 CHAPTER ASSESSMENT Understanding Main Ideas (Part B) The diagram below represents different izations of the orbitals of three carbon atoms, labeled X, Y, and Z. Use the diagram to answer the questions that follow. sp 3 X Y Z C sp 2 C p orbital (above and below) sp 2 p orbital (above and below) sp C p orbital (above and below) sp sp 3 sp 3 sp 3 sp 2 1. Write the electron configuration of an unbonded carbon atom (atomic number 6) before ization occurs. 2. Look at carbon atom X in the diagram. What is the symbol for the orbitals formed by carbon atom X? How many of them are there in that atom? 3. Does carbon atom X have any unized orbitals? If so, tell how many and write the symbol for them. 4. To how many other atoms would carbon atom X be attached? What types of bonds single, double, or triple would they be? State whether each attachment would involve sigma bonds, pi bonds, or both. 5. What would be the shape of the molecule formed by carbon atom X when it bonds in that way? 6. Suppose that the attachments in that molecule are to atoms of the same kind with an electronegativity greater than that of carbon. Would each bond be polar or nonpolar? Would the molecule as a whole be polar or nonpolar? Explain. 7. Look at carbon atom Y in the diagram. What is the symbol for the orbitals formed by carbon atom Y? How many of them are there in that atom? 108 Chemistry: Matter and Change Chapter 8 Chapter Assessment

10 CHAPTER ASSESSMENT Thinking Critically The graph shows the electronegativities of the elements of periods 2 and 3 of the periodic table, except for the noble gases. Use the graph to answer the following questions. Electronegativity Li Na Be Mg B Al Period 2 C Si Period Group number N P O S F Cl 1. If two atoms of differing electronegativity are bonded covalently to each other, what is true of the electrons they share? What type of bond results in such a case? 2. How does the electronegativity of boron (B) compare with that of nitrogen (N)? In terms of the periodic table, how are these two elements related? Compare aluminum (Al) with phosphorus (P) in the same way. 3. Describe the trend in electronegativity illustrated for period-2 and period-3 elements. 4. How does the electronegativity of boron (B) compare with that of aluminum (Al)? In terms of the periodic table, how are these two elements related? Compare nitrogen (N) with phosphorus (P) in the same way. 5. Describe the trend in electronegativity within a group of the periodic table, as suggested by the graph. Chapter Assessment Chemistry: Matter and Change Chapter 8 109

11 CHAPTER ASSESSMENT Applying Scientific Methods A college chemistry student is studying the properties of four unknown compounds, W, X, Y, and Z. She has been informed that one of them is ionic and that the other three are covalent. Of the latter, she has been told that the attractions between the formula units are dispersion forces in one case, hydrogen bonds in another, and covalent (network) bonds in another. She has been asked to determine the type of attractions for each substance. In an attempt to do so, she carries out experiments that reveal information about the substances properties. Use this information to answer the questions that follow. Property Unknown W Unknown X Unknown Y Unknown Z Hardness of solid soft soft brittle brittle Melting point ( C) Boiling point ( C) Solubility in polar solvent very soluble insoluble very soluble insoluble Solubility in nonpolar solvent insoluble very soluble insoluble insoluble Conductivity of solid nonconducting nonconducting nonconducting nonconducting Conductivity of liquid nonconducting nonconducting conducting nonconducting 1. On the basis of the results of her hardness test, the student concludes that unknowns W and X are covalent substances, and that either Y or Z is the ionic substance. Comment on the soundness of her conclusion, given only the hardness information. 2. The student examines the melting-point data, but claims that it is not useful in determining the substances types of attractions. How would you reply to that claim? 3. On the basis of the results of the boiling-point and melting-point tests, the student concludes that W is the hydrogen-bonded substance and that X must therefore be the substance that has the dispersion forces. Is that conclusion valid? Explain. 110 Chemistry: Matter and Change Chapter 8 Chapter Assessment

12 CHAPTER ASSESSMENT Applying Scientific Methods, continued 4. On the basis of the results of her solubility test, the student concludes that X must be covalent. Comment, and state any further conclusions that can be derived about the other substances. 5. On the basis of her electrical conductivity test, the student states that there must be some error because unknown Y acts like a covalent substance when solid but like an ionic substance when melted. Comment on her statement. 6. The student examines the entire set of data but is unable to come to final, definite conclusions about the substances types of attractions. Is it possible to do so, given the data? Explain, and state your own conclusions if any. 7. How do the overall procedure and your reasoning illustrate scientific methods? Chapter Assessment Chemistry: Matter and Change Chapter 8 111