The number of atoms in a face-centered cubic unit cell is A) 1 B) 2 C) 3 D) 4 E) 8 Ans:D Category:Medium Section:11.4 19. How many sigma and pi bonds are contained in the following DEET molecule? A) BeCl2 B) Br2 C) BF3 D) IBr E) CO2 Ans:D Category:Medium Section:10.2 21. The attractive energy between two ions is proportional to 1/r, whereas the attractive energy between two dipoles is proportional to 1/r6. Use the graph of vapor pressure to determine the normal boiling point of CHCl3. In nuclear fission, a nucleus of uranium-238, which contains 92 protons, can divide into two smaller spheres, each having 46 protons and a radius of 5.9010155.90 \times 10 - 155.901015 m. What is the magnitude of the repulsive electric force pushing the two spheres apart? The effect of increasing the pressure is to raise the boiling point. c. heat of freezing (solidification), heat of condensation H o w m u c h e n e r g y ( h e a t ) i s r e q u i r e d t o c o n v e r t 5 2 . Intermolecular forces are generally much weaker than covalent bonds. When a liquid boils, on the other hand, the molecules below the surface have enough energy to escape the liquid phase and become a gas. W h a t t y p e o f c h e m i c a l b o n d h o l d s t h e a t o m s t o g e t h e r w i t h i n a w a t e r m o l e c u l e ? If the structure of a molecule is such that the individual bond dipoles do not cancel one another, then the molecule has a net dipole moment. b. heat of fusion, heat of vaporization London was able to show with quantum mechanics that the attractive energy between molecules due to temporary dipoleinduced dipole interactions falls off as 1/r6. Which one of the following substances is expected to have the highest boiling point? a. London-dispersion forces b. ion-dipole forces c. ionic bonding d. dipole-dipole forces Bond strength rated strongest to weakest:Ionic > H-bond > Dipole > van der Waals Fewer functional groups > More functional groups (Amide>Acid>Alcohol>Ketone or Aldehyde>Amine>Ester>Alkane). Cs 2. C) a dispersion force. The heat capacity of liquid water is 4.18 J/gC and the heat of vaporization is 40.7 kJ/mol. All molecules have kinetic energy; they are vibrating. Which one of the following is most likely to be an ionic compound? As a result, it is relatively easy to temporarily deform the electron distribution to generate an instantaneous or induced dipole. D) polar bonds, but is a nonpolar molecule. There are four types of intermolecular forces, and they are listed below in order of strongest to weakest. A) NH3 B) CCl4 C) CO2 D) SF4 E) PCl5 Ans:B Category:Medium Section:10.1 17. E) trigonal pyramidal. Compounds such as HF can form only two hydrogen bonds at a time as can, on average, pure liquid NH3. In addition, the attractive interaction between dipoles falls off much more rapidly with increasing distance than do the ionion interactions. A) H2O B) BF3 C) Cl2 D) SiH4 E) Ar. Because the electron distribution is more easily perturbed in large, heavy species than in small, light species, we say that heavier substances tend to be much more polarizable than lighter ones. Which one of the following is most likely to be a covalent compound? Of the following substances, __________ has the highest boiling point. A) H2S B) HCN C) BF3 D) H2CO E) SO2 Ans:B Category:Medium Section:10.1 13. b. directly proportional to one another Ans: Category:Medium 42. Give the number of lone pairs around the central atom and the molecular geometry of XeF4. Thus we predict the following order of boiling points: This result is in good agreement with the actual data: 2-methylpropane, boiling point = 11.7C, and the dipole moment () = 0.13 D; methyl ethyl ether, boiling point = 7.4C and = 1.17 D; acetone, boiling point = 56.1C and = 2.88 D. Arrange carbon tetrafluoride (CF4), ethyl methyl sulfide (CH3SC2H5), dimethyl sulfoxide [(CH3)2S=O], and 2-methylbutane [isopentane, (CH3)2CHCH2CH3] in order of decreasing boiling points. The net effect is that the first atom causes the temporary formation of a dipole, called an induced dipole, in the second. The polarizability of a substance also determines how it interacts with ions and species that possess permanent dipoles. (iii) Viscosity increases as intermolecular forces increase. Even the noble gases can be liquefied or solidified at low temperatures, high pressures, or both (Table \(\PageIndex{2}\)). The Lewis structure for CS2 is: A) EMBED Equation.BREE4 B) EMBED Equation.BREE4 C) EMBED Equation.BREE4 D) EMBED Equation.BREE4 Ans:C Category:Medium Section:9.6 30. The number of lone electron pairs in the NO2 ion is ___. 0 9 J / g C DH f u s = 6 . What is the formal charge on the oxygen atom in N2O (the atomic order is NNO)? B) ion-dipole forces. b. body-centered cubic Ans:E Category:Medium Section:10.1 6. a. C2Br6 b. C2F6 c. C2I6 d. C2Cl6 e. C2H6, What is the predominant intermolecular force in CBr4? 0 4 F J Z \ ^ xfW jl5(M A) KF B) KI C) LiF D) LiI E) NaF Ans:C Category:Medium Section:9.3 15. Write the Lewis dot symbol for the sulfide ion. A.Hydrogen bonds involve hydrogen bonded to carbon, nitrogen, oxygen, or fluorine. Intermolecular forces are electrostatic in nature and include van der Waals forces and hydrogen bonds. Each unit cell contains __________ Cs+ ions and __________ Cl-, ions, respectively. The one compound that can act as a hydrogen bond donor, methanol (CH3OH), contains both a hydrogen atom attached to O (making it a hydrogen bond donor) and two lone pairs of electrons on O (making it a hydrogen bond acceptor); methanol can thus form hydrogen bonds by acting as either a hydrogen bond donor or a hydrogen bond acceptor. Give the number of lone pairs around the central atom and the molecular geometry of XeF2. __________ solids consist of atoms or molecules held together by dipole-dipole forces, London disperson forces, and/or hydrogen bonds. C) molecular crystal. Consequently, N 2 O should have a higher boiling point. a. monoclinic Which property of water allows a razor blade to float on it without sinking? 11. Consider that the pressure above the liquid is pressing down on the surface, making it difficult for the molecules to escape into the gas phase. Video Discussing London/Dispersion Intermolecular Forces. Acetic acid has a heat of fusion of 10.8 kJ/mol and a heat of vaporization of 24.3 kJ/mol. A . Ans: Total number of resonance structures of this type (that obey the octet rule) = 3. Ans: Category:Medium Section:9.6 48. Which of the following would be expected to have the lowest vapor pressure at room temperature? These interactions become important for gases only at very high pressures, where they are responsible for the observed deviations from the ideal gas law at high pressures. This molecule has an H atom bonded to an O atom, so it will experience hydrogen bonding. How many atoms are there per unit cell? h|g CJ UVaJ h>* B*ph j h>* B*Uph h' h>* H*h>* h h CJ$ aJ$ h>* CJ$ aJ$ @ c L | } , very soft According to the VSEPR theory, the molecular geometry of boron trichloride is A) linear B) trigonal planar C) bent D) tetrahedral E) trigonal pyramidal Ans:B Category:Medium Section:10.1 11. The ease with which the charge distribution in a molecule can be distorted by an external electrical field is called the __________. Which one of the following substances is expected to have the highest boiling point? Which of the following solids would have the highest melting point? In which of the following molecules is hydrogen bonding likely to be the most significant component of the total intermolecular forces? e. heat of deposition, heat of vaporization. 1and8 These attractive interactions are weak and fall off rapidly with increasing distance. Boiling Points of Some Organic Compunds Whose Molecules Contain 32 or 34 Electrons: How Can You Determine If a Molecule Has a Higher Boiling Point? C) polar bonds, and is a polar molecule. 8 2 9 . Arrange C60 (buckminsterfullerene, which has a cage structure), NaCl, He, Ar, and N2O in order of increasing boiling points. A bonding molecular orbital is of lower energy (more stable) than the atomic orbitals from which it was formed. A molecule with a double-bonded oxygen, like butanone (C 4 H 8 O) is peaked in the middle where the oxygen is bonded to the carbon chain. Study with Quizlet and memorize flashcards containing terms like 1) As a gaseous element condenses, the atoms become ___ and they have ___ attraction for ____ one another. Ans: dipole-dipole and dispersion Category:Medium Section:11.2 32. A) Li B) Cs C) P D) As E) Ge Ans:C Category:Medium Section:9.5 17. Give the number of lone pairs around the central atom and the molecular geometry of SCl2. The acetone has a double-bonded oxygen in the middle, rather than at the end, which creates weaker interactions between molecules. Although hydrogen bonds are significantly weaker than covalent bonds, with typical dissociation energies of only 1525 kJ/mol, they have a significant influence on the physical properties of a compound. Because the boiling points of nonpolar substances increase rapidly with molecular mass, C 60 should boil at a higher temperature than the other nonionic substances. This effect, illustrated for two H2 molecules in part (b) in Figure \(\PageIndex{3}\), tends to become more pronounced as atomic and molecular masses increase (Table \(\PageIndex{2}\)). a. ion-ion interactions b. hydrogen bonding c. ion-dipole interactions d. dipole-dipole interactions e. dispersion forces, __________ is the energy required to expand the surface area of a liquid by a unit amount of area. Of the compounds that can act as hydrogen bond donors, identify those that also contain lone pairs of electrons, which allow them to be hydrogen bond acceptors. Write a Lewis structure for OF2. How many sigma bonds and pi bonds are contained in a ibuprofen molecule? CsCl crystallizes in a unit cell that contains the Cs+ ion at the center of a cube that has a Cl- at each corner. b. Ethanol has a higher boiling point because of greater London dispersion force c. Both hexane and . In contrast, each oxygen atom is bonded to two H atoms at the shorter distance and two at the longer distance, corresponding to two OH covalent bonds and two OH hydrogen bonds from adjacent water molecules, respectively. Of the species listed, xenon (Xe), ethane (C2H6), and trimethylamine [(CH3)3N] do not contain a hydrogen atom attached to O, N, or F; hence they cannot act as hydrogen bond donors. Consequently, we expect intermolecular interactions for n-butane to be stronger due to its larger surface area, resulting in a higher boiling point. Which one of the following compounds does not follow the octet rule? In contrast to intramolecular forces, such as the covalent bonds that hold atoms together in molecules and polyatomic ions, intermolecular forces hold molecules together in a liquid or solid. Which one of the following molecules has a non-zero dipole moment? Heat of sublimation can be approximated by adding together __________ and __________. Which of the following substances will display an incomplete octet in its Lewis structure? A) CH3OCH3 B) CH3CH2CH3 C) CH3CHO D) CH3OH E) CH3CN. Doubling the distance (r 2r) decreases the attractive energy by one-half. 6 k J D ) 2 7 , 6 0 0 J E ) 2 5 , 0 0 0 k J A n s : A C a t e g o r y : M e d i u m S e c t i o n : 1 1 . A) SF4 B) XeF4 C) NF3 D) SF6 E) PF5 Ans:E Category:Medium Section:10.1 14. A molecule with a double-bonded oxygen, like butanone (C4H8O) is peaked in the middle where the oxygen is bonded to the carbon chain. Argon and N2O have very similar molar masses (40 and 44 g/mol, respectively), but N2O is polar while Ar is not. B) nonpolar bonds, but is a polar molecule. D) Ice is more dense than liquid water. In general, however, dipoledipole interactions in small polar molecules are significantly stronger than London dispersion forces, so the former predominate. As a result, the CO bond dipoles partially reinforce one another and generate a significant dipole moment that should give a moderately high boiling point. A 6.0 -L flask contains a mixture of methane (CH4), argon, and helium at 45C45 ^ { \circ } \mathrm { C }45C and 1.75 atm. The expansion of water when freezing also explains why automobile or boat engines must be protected by antifreeze and why unprotected pipes in houses break if they are allowed to freeze. e. hydrogen bonding, . Bodies of water would freeze from the bottom up, which would be lethal for most aquatic creatures. m n x y ) * 4 5 ? Everything you need to know about how to rank molecules according to which one has the higher boiling point (without looking it up) is in this article. Let's start with some basics. To predict the relative boiling points of the other compounds, we must consider their polarity (for dipoledipole interactions), their ability to form hydrogen bonds, and their molar mass (for London dispersion forces). c. 1 and 1 Indicate all the types of intermolecular forces of attraction in C2H6(g). Although CH bonds are polar, they are only minimally polar. The three major types of intermolecular interactions are dipoledipole interactions, London dispersion forces (these two are often referred to collectively as van der Waals forces), and hydrogen bonds. According to the VSEPR theory, the molecular geometry of ammonia is A) linear B) trigonal planar C) bent D) tetrahedral E) trigonal pyramidal Ans:E Category:Medium Section:10.1 12. Which of the following solids would have the highest melting point? Interactions between these temporary dipoles cause atoms to be attracted to one another. Conversely, \(\ce{NaCl}\), which is held together by interionic interactions, is a high-melting-point solid. The vapor pressure of a liquid in a closed container depends upon A) the amount of liquid. A hydrogen bond is usually indicated by a dotted line between the hydrogen atom attached to O, N, or F (the hydrogen bond donor) and the atom that has the lone pair of electrons (the hydrogen bond acceptor). If you are comparing molecules to determine which has the higher boiling point, consider the forces that are at work within the molecule. A) CH4 B) Cl2 C) Kr D) CH3Cl E) N2 Ans:D Category:Medium Section:11.2 7. Ans: Category:Medium 41. dimethyl sulfoxide (boiling point = 189.9C) > ethyl methyl sulfide (boiling point = 67C) > 2-methylbutane (boiling point = 27.8C) > carbon tetrafluoride (boiling point = 128C). A) CO2 B) C2H2 C) SO2 D) BeCl2 E) KrF2 Ans:C Category:Medium Section:10.1 15. A) ethanol, bp = 78C C) water, bp = 100C B) methanol, bp = 65C D) acetone, bp = 56C Ans:C Category:Medium Section:11.8 11. Because the electrons are in constant motion, however, their distribution in one atom is likely to be asymmetrical at any given instant, resulting in an instantaneous dipole moment. Consequently, HO, HN, and HF bonds have very large bond dipoles that can interact strongly with one another. A) ClF3 B) FeCl3 C) NH3 D) PF3 E) SO3 Ans:B Category:Easy Section:9.2 3. A polar covalent bond would form in which one of the following pairs of atoms? B R E E 4 B ) E M B E D E q u a t i o n . d. is highly cohesive E) hydrogen bonding. A ) I o n i c b o n d C ) P o l a r c o v a l e n t b o n d B ) N o n p o l a r c o v a l e n t b o n d D ) C o o r d i n a t e c o v a l e n t b o n d A n s : C C a t e g o r y : M e d i u m S e c t i o n : 9 .