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This 8 page Class Notes was uploaded by Cole White IV on Monday October 5, 2015. The Class Notes belongs to CHEM32 at City College of San Francisco taught by JamesArmstrong in Fall. Since its upload, it has received 32 views. For similar materials see /class/219529/chem32-city-college-of-san-francisco in Chemistry at City College of San Francisco.
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Date Created: 10/05/15
CHAPTER 3 ANSWERS TO SELECTED PROBLEMS SAMPLE PROBLEMS Try it yourself 3 1 Cl l t 3 2 H Cl 33 Selenium needs two more electrons to satisfy the octet rule and uorine needs one The simplest combination that satis es the octet rule is one Se atom bonded to two F atoms to form a molecule of Ser The Lewis structure of this molecule is 36 H CE C C H 37 In CF3Cl carbon must make four bonds while uorine and chlorine each make one bond based on their numbers of valence electrons Therefore carbon is in the center of the molecule surrounded by the four other atoms The structure of this molecule is 38 Structure a is the only one that has the normal numbers of bonds for each atom three for nitrogen four for carbon and one for each hydrogen and has both carbon and nitrogen satisfying the octet rule so structure b is the only reasonable structure 39 There is only one possible structure but there are several ways to draw it The correct answer has the carbon atom bonded to three hydrogens and the oxygen with the remaining hydrogen bonded to the oxygen H H c 39C3 H I I I H 310 Chlorine has the stronger attraction for electrons 311 The electronegativity of nitrogen is higher than that of carbon so the carbon atom is positively charged and the nitrogen atom is negatively charged 312 a phosphorus penta uoride b disulfur dichloride 313 SF5 314 Calcium has two valance electrons and sulfur has siX These two atoms can satisfy the octet rule by transferring two electrons from calcium to sulfur The calcium atom becomes an calcium ion Ca2 and the sulfur atom become a sulfide ion Szi Q Ca 28 gt Ca 315 Selenium is in Group 6A so it will gain two electrons to form an ion with a 72 charge The symbol for this ion is Self 316 Nitrogen needs three additional electrons to satisfy the octet rule but lithium only has one valence electron Therefore we need three lithium atoms to supply the three valence electrons that nitrogen needs The lithium atoms become Li ions and the nitrogen atom becomes a N37 ion These ions then combine to form an ionic compound Li3N Li L 317 We need two Na ions to balance the charge on 82 so the chemical formula is NazS 318 The correct formula is Mg3N2 319 CuS and Cqu Remember that Cu makes two ions Cu2 and Cu but sulfur can only make S T 320 Sodium oxide 321 K20 and Ale3 322 ChromiumH chloride or chromic chloride 323 CoF3 324 FeOH3 325 Magnesium phosphate 326 CuSO4 327 a Ionic because Hg is a metal and Cl is a nonmetal b Molecular because all of the elements in this compound are nonmetals 328 Fe203 is an ionic compound and is called ironIII oxide N203 is a molecular compound and is called dinitrogen trioxide END OF SECTION PROBLEMS Section 31 31 a Br does not satisfy the octet rule b Kr satis es the octet rule 32 a HzBr b HifiH 0 HCI H I 33 Silicon has four valence electrons so it has four empty spaces in its valence shell As a result silicon normally forms four covalent bonds allowing it to complete its octet 34 Any of the group 6A elements oxygen sulfur selenium tellurium or polonium Section 32 35 a 11IQ b 939 c HCCH Section 33 36 The silicon atom is at the center because it must make four covalent bonds The other atoms only form one covalent bond apiece 2211 H H 37 a 51 13 51 b H c c H H H 38 a b H C s c H cEN 39 Structures a and b are reasonable while c and d are not In structure c the lefthand carbon atom and the neighboring oxygen atom have the wrong numbers of bonds and in structure d two of the three oxygen atoms have the wrong numbers of bonds Section 34 310 From Table 32 we can see that uorine has the highest electronegativity in Group 7A and astatine At has the lowest so uorine has the strongest attraction for electrons and astatine has the weakest 311 a Nitrogen has a lower electronegativity than oxygen so nitrogen is positively charged b Hydrogen has a lower electronegativity than chlorine so hydrogen is positively charged c The two nitrogen atoms have equal attractions for electrons so neither atom has a charge 3 12 Chlorine has a higher electronegativity than carbon so the chlorine atom is negatively charged Section 35 3 13 a phosphorus penta uoride b nitrogen monoxide c disulfur tetra uoride 314 a P13 b BrCl c N205 Section 36 315 Calcium has the following electron arrangement shell 1 2 electrons shell 2 8 electrons shell 3 8 electrons shell 4 2 electrons If calcium loses the two electrons from shell 4 it becomes an ion with the following arrangement shell 1 2 electrons shell 2 8 electrons shell 3 8 electrons The atom now has eight electrons in its outermost occupied shell so it satisfies the octet rule 316 Sulfur has the following electron arrangement shell 1 2 electrons shell 2 8 electrons shell 3 6 electrons If sulfur gains two additional electrons it becomes an ion with the following arrangement shell 1 2 electrons shell 2 8 electrons shell 3 8 electrons The atom now has eight electrons in its outermost occupied shell so it satisfies the octet rule 317 The calcium atom becomes an ion with a 2 charge and the sulfur atom becomes an ion with a 2 charge 318 Both of these ions have the following electron arrangement shell 1 2 electrons shell 2 8 electrons Since each ion has eight electrons in its outermost shell both ions satisfy the octet rule 319 a Potassium loses electrons with each atom losing one electron b Sulfur gains electrons with each atom gaining two electrons c The potassium atoms have a 1 charge and the sulfur atoms have a 2 charge d We need two potassium atoms to supply the two electrons needed by sulfur so the formula of the compound is KzS Section 37 320 a NazSe b Ser c Cr13 d Mg3Nz 321 a KBr b ZnClz c A12S3 d C00 and C0203 322 a The charge on the copper ion is 2 b The charge on the copper ion is 1 Section 38 323 a potassium oxide b magnesium sulfide c copperII chloride or cupric chloride d chromiumIII oxide or chromic oxide 324 a NaF b CaIz c MnS d FeC13 e ZnO Section 39 325 a ZnOH2 b AngO4 c K3PO4 d NH4Br 326 a CaC03 b Mg3PO4z c CrOH3 d CoN03z 327 a potassium hydrogen carbonate or potassium bicarbonate b sodium carbonate c ammonium sulfate Section 310 I l I C O l I 7 328 1Br Na In IBT the two atoms ffmn a NaBr contains two ions that COValenl bond by Sharlng a are attracted to one another palr 0f eleCtFOIlS The atoms do not share electrons 329 a ionic b molecular c ionic d molecular 330 a sulfur dichloride b magnesium chloride CUMULATIVE PROBLEMS Odd numbered problems only 331 Neon Ne has eight valence electrons and satis es the octet rule 333 Helium does not have eight valence electrons It is placed in Group SA because its chemical properties are similar to those of the elements that have eight valence electrons and different from the other elements that have two valence electrons 335 Choice b is the most reasonable arrangement of atoms Oxygen normally makes two covalent bonds while hydrogen and chlorine make only one so oxygen should be the central atom i 337 a H 39s39 H b39139 quot 39139 cF As 39F39 Zli d31 T e HC39S39 f Br CEC l3i 21 H g H O Nquot 339 A magnesium atom has only two valence electrons so it can only form two bonds Each bond contributes one additional electron to the atom so the atom ends up with four electrons in its outer shell As a result Mg cannot satisfy the octet rule by forming covalent bonds 0 H n I H H 0 9 341 g c CI C H 343 Structure 1 is reasonable because each carbon atom forms four covalent bonds 345 There are two other structures that obey the normal bonding requirements of carbon and hydrogen and satisfy the octet rule H H C H CCC H and H CC H Structures such as the ones below are equivalent to structure 1 in the problems H T H CEC C H H T H H CEO H 347 Z forms two covalent bonds so an individual atom of element Z must have six valence electrons The only element in Period 3 that has six valence electrons is sulfur X forms one covalent bond so each atom of X must have seven valence electrons The only element in Period 3 that has seven valence electrons is chlorine Therefore X is chlorine and Z is sulfur 349 a carbon b nitrogen c There is no positively charged atom 351 a CF4 b 802 353 a chlorine trifluoride b dinitrogen tetra uoride c carbon monoxide 355 Aluminum has the following electron arrangement shell 1 2 electrons shell 2 8 electrons shell 3 3 electrons When aluminum loses the three electrons from shell 3 it becomes an ion with a 3 charge and the following arrangement shell 1 2 electrons shell 2 8 electrons The atom now has eight electrons in its outermost occupied shell so it satisfies the octet rule 357 a 2 b 71 c 72 d 1 359 The Group 7A elements form ions that have a 71 charge 361 Any element in Group 2A forms a 2 ion Be Mg Ca Sr Ba and Ra 363 Calcium has two valence electrons and oxygen has six These atoms can share no more than four electrons because calcium can only contribute two electrons to the bond If the atoms share four electrons oxygen satisfies the octet rule but calcium does not as shown below Ca 0 gt CaO 365 Formulas b and c obey the rule of charge balance while a and d do not 367 a MgBrz b CoF3 c NH4zS d AngO4 369 a magnesium bromide b cobaltIH uoride or cobaltic uoride c ammonium sul de d silver sulfate 371 Each sodium ion has a 1 charge so the total positive charge in this compound is 2 The compound must satisfy the rule of charge balance so the chromate ion must have a 2 charge 373 a 2 b 4 c 3 375 CuzC03 7 copperI carbonate contains Cu CuC03 7 copperII carbonate contains Cu2 377 a ZnBrz b Na3N c Ag3P04 dNiOHz e KHCO3 fCrN033 g CuZO h NH4I 379 a CaClz is an ionic compound and must be named using the rules for ionic compounds The correct name is calcium chloride b Fe can form either a 2 or a 3 ion and the name of the compound must tell which ion is present The correct name is ironH oxide Ferrous oxide is also correct c The N03 group is a polyatomic ion N037 This ion is called nitrate so the correct name of the compound is sodium nitrate 381 a ionic b molecular c molecular d ionic 383 a calcium oxide b carbon monoxide c nitrogen tri uoride d ironIII uoride or ferric uoride 385 NaCl contains Na and C17 ions which attract one another because they have opposite charges The sodium and chlorine atoms do not share electrons in NaCl In HCl the two atoms do share electrons o o i o 0 Na Cl H Cl NaCl no electron sharing HCl electron sharing 387 Ions that the same charge both positive or both negative repel one another so Na and K cannot come together to form a stable compound 6 389 6 0 6
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