Compound Structure and Properties

Compound structure and properties 1. Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms? A. B. D. C. Answer B Correct. Being the same size, copper atoms and zinc atoms would form a substitutional alloy in which the atoms substitute for one another in a lattice of positive cores immersed in a sea of electrons. 2. On the basis of the information above, which of the following arranges the binary compounds in order of increasing bond polarity? A. CH4 < SiCl4 < SF4 B. CH4 < SF4 < SiCl4 C. SF4 < CH4 < SiCl4 D. SiCl4 < SF4 < CH4 3. Which of the following has the bonds arranged in order of decreasing polarity? A. H-F>N-F>F-F C. O-N> O-S> O-Te B. H-I>H-Br>H-F D. Sb-I>Sb-Te>Sb-Cl 4. Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°? A. B. C. D. Answer DThe carbon atom attached to the oxygen atoms exhibits sp2 hybridization, thus the bond angles around it are close to 120°. Another explanation is, the carbon atom attached to the two oxygen atoms is surrounded by three electron domains, which, according to VSEPR theory, will repel one another to produce a trigonal planar geometry around that atom. 5. A particle-level diagram of a metallic element is shown above. Typically, metals are both malleable and ductile. The best explanation for these properties is that the electrons involved in bonding among metal atoms are A. unequally shared and form nondirectional bonds C. equally shared and form nondirectional bonds B. unequally shared and form highly directional bonds D. equally shared and form highly directional bonds Answer C In metals, electrons are free to move as described by the electron sea model. Electrons are shared equally among atoms, and the structure is based on simple close-packed structures that contain no fixed directional bonds. 6. Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are A. the same because the molecular formulas are similar B. the same because C and S have similar electronegativity values C. different because the lone pair of electrons on the S atom make it the negative end of a dipole D. different because S has a greater number of electron domains (regions of electron density) surrounding it than C has Answer D Both the C-O and S-O bonds are polar, due to the different electronegativities of the bonded atoms. However, the CO2 molecule is linear and so the bond dipoles cancel and the molecule has no net dipole. In SO2, the molecule is bent and so the bond dipoles do not cancel and a net dipole is present. The polarity of the two substances differs because of the differences in geometry, which is a direct consequence of the number of electron domains around the central atom (2 in CO2and 3 in SO2), as stated in this option. 7. Two pure elements react to form a compound. One element is an alkali metal, X, and the other element is a halogen, Z. Which of the following is the most valid scientific claim that can be made about the compound? A. It has the formula XZ2. B. It does not dissolve in water. C. It contains ionic bonds. D. It contains covalent bonds. Answer C An alkali metal will readily lose an electron and a halogen will readily gain an electron to form an ionic compound with a 1:1 ratio of X+:Z− ions. 8. The elements C and Se have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from C and Se is most likely to be true? A. The carbon-to-selenium bond is unstable. B. The carbon-to-selenium bond is nonpolar covalent. C. The compound has the empirical formula CSe. D. A molecule of the compound will have a partial negative charge on the carbon atom. Answer B The bonding in compounds between elements with the same (or only slightly different) electronegativity values will exhibit covalent bonding (that is, more or less equal sharing of electrons). 9. Which of the following correctly indicates whether the solid represented by the particulate model shown above conducts electricity and explains why or why not? A. It conducts electricity because it is made of positive and negative ions. B. It conducts electricity because it is made of particles of different sizes. C. It does not conduct electricity because its ions cannot move freely within the solid. D. It does not conduct electricity because there are small spaces between the particles. Answer C In the solid state, the ions are held by strong coulombic forces in fixed positions within the lattice; thus they cannot move or migrate through the lattice. 10. The particle-level diagram above represents the structure of solid KF. Although the molar mass of KClis greater than that of KF, the density of KCl is actually less than that of KF. Which of the following representations of the structure of KCl best helps to explain this phenomenon? A. B. C. D. Answer A The diagram shows that the chloride ions are larger than the fluoride ions, which causes the interionic distances in the solid to increase to the point where the effect of the larger spacing among ions in KCl is greater than the effect of the larger mass of the chlorine on the density. Refer to the following diatomic species (A) Li2 (B) B2 (C) N2 (D) O2 (E) F2 11. Contains 1 sigma (σ) and 2 pi (π) bonds A. Li2 B. B2 C. N2 D. O2 E. F2 12. Has a bond order of 2 A. Li2 B. B2 C. N2 D. O2 E. F2 13. Has the largest bond-dissociation energy A. Li2 B. B2 C. N2 D. O2 E. F2 14. The geometry of the SO3 molecule is best described as A. trigonal planar B. trigonal pyramidal C. square pyramidal 15. [D] The question refers to the following species. (A) H2O D. bent (B) NH3 (C) BH3 (D) CH4 (E) SiH4 16. Is predicted to have the largest bond angle E. tetrahedral A. H2O B. NH3 C. BH3 D. CH4 E. SiH4 17. Which of the following Lewis diagrams best represents the bonding in the N2O molecule, considering formal charges? A. B. C. D. Answer B When the formal charge of each atom in this diagram is determined using the rule: (formal charge of an atom = the number of valence electrons of the atom − (the number of electrons in lone pairs + half the number of electrons in bonds with other atoms)). The sum of the formal charges on all the atoms in N2O is equal to zero. The most favored structure considers the minimization of the formal charges and the electronegativities of the atoms. Oxygen is more electronegative than nitrogen; therefore, the Lewis diagram that shows a negative formal charge on the oxygen atom is the best for depicting the molecule. 18. Which of the following statements, if true, would support the claim that the NO3− ion, represented above, has three resonance structures? A. The NO3− ion is not a polar species. B. The oxygen-to-nitrogen-to-oxygen bond angles are 90°. C. One of the bonds in NO3− is longer than the other two. D. One of the bonds in NO3− is shorter than the other two. Answer A If the NO3− ion did NOT have three equivalent structures, then the ion would be polar because of the unequal distribution of charge within the ion. Equal contributions of the three resonance forms to the structure of the ion result in a planar ion with three equivalent polar nitrogen-oxygen bonds. Due to the trigonal planar symmetry of the NO3− ion, the negative dipoles cancel out. 19. Lewis diagrams of molecules of three different hydrocarbons are shown above. Which of the following claims about the molecules is best supported by the diagrams? A. All the atoms in molecule 1 lie in one plane. B. All the molecules have the same empirical formula. C. The C-C-C bond angle in molecule 2 is close to 180°. D. The strongest carbon-to-carbon bond occurs in molecule 3. Answer D Molecule 3 contains a triple bond between two carbon atoms. Between two of the same kind of atom, triple bonds are stronger than double bonds, which in turn are stronger than single bonds. 20. In the following diagrams, elements are represented by X and Z, which form molecular compounds with one another. Which diagram represents a molecule that has a bent molecular geometry? A. B. C. D. Answer B There are four electron domains around the central atom X, and their geometry is tetrahedral, which minimizes the repulsion between the four electron pairs. The Z-X-Z bond angle is approximately 109.5°, and the molecular geometry is bent. 21. For which of the following molecules are resonance structures necessary to describe the bonding satisfactorily? A. H2S B. SO2 C. CO2 D.OF2 E. PF3 22. Which of the following molecules has an angular (bent) geometry that is commonly represented as a resonance hybrid of two or more electron-dot structures? A. CO2 B. O3 C. CH4 D. BeF2 E. OF2 23. Which of the following molecules contains exactly three sigma (σ) bonds and two pi (π) bonds? A. C2H2 B. CO2 C. HCN D. SO3 E. N2 24. Resonance is most commonly used to describe the bonding in molecules of which of the following? A. CO2B B. O3 C. H2O D. CH4 E.SF6 25. Steel is an alloy containing Fe atoms and C atoms. Which of the following diagrams best represents the particlelevel structure of steel? B. A C D Answer B C is in the second period and has two electron shells, whereas Fe is in the fourth period and has four electron shells; thus C atoms are smaller than Fe atoms. The diagram shows how the smaller C atoms occupy the spaces (interstices) between the larger Fe atoms in an interstitial alloy. 26. The electron-dot structure (Lewis structure) for which of the following molecules would have two unshared pairs of electrons on the central atom? A. H2S B. NH3 C. CH4 D. HCN E.CO2 27. The melting point of MgO is higher than that of NaF. Explanations for this observation include which of the following? I. Mg2+ is more positively charged than Na+. II. O2- is more negatively charged than F-. III. The O2- ion is smaller than the F- ion. A. II only B. I and II only. C. I and III only. D. II and III only E.I, II, and III 28. The BF3 molecule is nonpolar, whereas the NF3 molecule is polar. Which of the following statements accounts for the difference in polarity of the two molecules? A. In NF3, each F is joined to N with multiple bonds, whereas in BF 3 , each F is joined to B with single bonds. B.N — F bonds are polar, whereas B — F bonds are nonpolar. C.NF3 is an ionic compound, whereas BF3 is a molecular compound. D. Unlike BF3, NF3 has a nonplanar geometry due to an unshared pair of electrons on the N atom. 29. [D] 30. Which of the following is a nonpolar molecule that contains polar bonds? A. F2 B. CHF3 C. CO2 D. HCl E.NH3 Compound structure and properties 1. Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms? A. B. D. C. 2. On the basis of the information above, which of the following arranges the binary compounds in order of increasing bond polarity? A. CH4 < SiCl4 < SF4 B. CH4 < SF4 < SiCl4 C. SF4 < CH4 < SiCl4 D. SiCl4 < SF4 < CH4 3. Which of the following has the bonds arranged in order of decreasing polarity? A. H-F>N-F>F-F C. O-N> O-S> O-Te B. H-I>H-Br>H-F D. Sb-I>Sb-Te>Sb-Cl 4. Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°? A. B. C. D. 5. A particle-level diagram of a metallic element is shown above. Typically, metals are both malleable and ductile. The best explanation for these properties is that the electrons involved in bonding among metal atoms are A. unequally shared and form nondirectional bonds B. unequally shared and form highly directional bonds C. equally shared and form nondirectional bonds 6. D. equally shared and form highly directional bonds Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are A. the same because the molecular formulas are similar B. the same because C and S have similar electronegativity values C. different because the lone pair of electrons on the S atom make it the negative end of a dipole D. different because S has a greater number of electron domains (regions of electron density) surrounding it than C has 7. Two pure elements react to form a compound. One element is an alkali metal, X, and the other element is a halogen, Z. Which of the following is the most valid scientific claim that can be made about the compound? A. It has the formula XZ2. B. It does not dissolve in water. C. It contains ionic bonds. D. It contains covalent bonds. 8. The elements C and Se have the same electronegativity value, 2.55. Which of the following claims about the compound that forms from C and Se is most likely to be true? A. The carbon-to-selenium bond is unstable. B. The carbon-to-selenium bond is nonpolar covalent. C. The compound has the empirical formula CSe. D. A molecule of the compound will have a partial negative charge on the carbon atom. 9. Which of the following correctly indicates whether the solid represented by the particulate model shown above conducts electricity and explains why or why not? A. It conducts electricity because it is made of positive and negative ions. B. It conducts electricity because it is made of particles of different sizes. C. It does not conduct electricity because its ions cannot move freely within the solid. D. It does not conduct electricity because there are small spaces between the particles. 10. The particle-level diagram above represents the structure of solid KF. Although the molar mass of KClis greater than that of KF, the density of KCl is actually less than that of KF. Which of the following representations of the structure of KCl best helps to explain this phenomenon? A. B. 11. Refer to the following diatomic species (A) Li2 (B) B2 (C) N2 (D) O2 (E) F2 Contains 1 sigma (σ) and 2 pi (π) bonds C. D. A. Li2 B. B2 C. N2 D. O2 E. F2 12. Has a bond order of 2 A. Li2 B. B2 C. N2 D. O2 E. F2 13. Has the largest bond-dissociation energy A. Li2 B. B2 C. N2 D. O2 E. F2 14. The geometry of the SO3 molecule is best described as A. trigonal planar B. trigonal pyramidal C. square pyramidal D. bent E. tetrahedral 15. 16. The question refers to the following species. (A) H2O (B) NH3 (C) BH3 (D) CH4 (E) SiH4 Is predicted to have the largest bond angle A. H2O B. NH3 C. BH3 D. CH4 E. SiH4 17. Which of the following Lewis diagrams best represents the bonding in the N2O molecule, considering formal charges? A. B. C. D. 18. Which of the following statements, if true, would support the claim that the NO3− ion, represented above, has three resonance structures? A. The NO3− ion is not a polar species. B. The oxygen-to-nitrogen-to-oxygen bond angles are 90°. C. One of the bonds in NO3− is longer than the other two. D. One of the bonds in NO3− is shorter than the other two 19. Lewis diagrams of molecules of three different hydrocarbons are shown above. Which of the following claims about the molecules is best supported by the diagrams? A. All the atoms in molecule 1 lie in one plane. B. All the molecules have the same empirical formula. C. The C-C-C bond angle in molecule 2 is close to 180°. D. The strongest carbon-to-carbon bond occurs in molecule 3. 20. In the following diagrams, elements are represented by X and Z, which form molecular compounds with one another. Which diagram represents a molecule that has a bent molecular geometry? A. B. C. D. 21. For which of the following molecules are resonance structures necessary to describe the bonding satisfactorily? A. H2S B. SO2 C. CO2 D.OF2 E. PF3 22. Which of the following molecules has an angular (bent) geometry that is commonly represented as a resonance hybrid of two or more electron-dot structures? A. CO2 B. O3 C. CH4 D. BeF2 E. OF2 23. Which of the following molecules contains exactly three sigma (σ) bonds and two pi (π) bonds? A. C2H2 B. CO2 C. HCN D. SO3 E. N2 24. Resonance is most commonly used to describe the bonding in molecules of which of the following? A. CO2B B. O3 C. H2O D. CH4 E.SF6 25. Steel is an alloy containing Fe atoms and C atoms. Which of the following diagrams best represents the particlelevel structure of steel? B. A C D 26. The electron-dot structure (Lewis structure) for which of the following molecules would have two unshared pairs of electrons on the central atom? A. H2S B. NH3 C. CH4 D. HCN E.CO2 27. The melting point of MgO is higher than that of NaF. Explanations for this observation include which of the following? I. Mg2+ is more positively charged than Na+. II. O2- is more negatively charged than F-. III. The O2- ion is smaller than the F- ion. A. II only B. I and II only. C. I and III only. D. II and III only E.I, II, and III 28. The BF3 molecule is nonpolar, whereas the NF3 molecule is polar. Which of the following statements accounts for the difference in polarity of the two molecules? A. In NF3, each F is joined to N with multiple bonds, whereas in BF 3 , each F is joined to B with single bonds. B.N — F bonds are polar, whereas B — F bonds are nonpolar. C.NF3 is an ionic compound, whereas BF3 is a molecular compound. D. Unlike BF3, NF3 has a nonplanar geometry due to an unshared pair of electrons on the N atom. 29. 30. Which of the following is a nonpolar molecule that contains polar bonds? A. F2 B. CHF3 C. CO2 D. HCl E.NH3