Chemistry Chapter 3 Notes PDF

1 Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel...

1 Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 3 Molecules, Ions and Their Compounds Lectures written by John Kotz ©2006 © 2006 Brooks/Cole Brooks/Cole Thomson - Thomson  Molecules, Ions & 2 Their Compounds NaCl, salt Ethanol, C2H6O Buckyball, C60 © 2006 Brooks/Cole - Thomson  3 Compounds & Molecules COMPOUNDS are a combination of 2 or more elements in definite ratios by mass. The character of each element is lost when forming a compound. MOLECULES are the smallest unit of a compound that retains the characteristics of the compound. © 2006 Brooks/Cole - Thomson  4 MOLECULAR FORMULAS Formula for glycine is C2H5NO2 In one molecule there are – 2 C atoms – 5 H atoms – 1 N atom – 2 O atoms © 2006 Brooks/Cole - Thomson  5 WRITING FORMULAS Can also write glycine formula as –H2NCH2COOH to show atom ordering or in the form of a structural formula H H O H N C C O H H © 2006 Brooks/Cole - Thomson  6 MOLECULAR MODELING H H O Structural formula H N C C O H of glycine H Ball & stick Space-filling © 2006 Brooks/Cole - Thomson  7 MOLECULAR WEIGHT AND MOLAR MASS Molecular weight = sum of the atomic weights of all atoms in the molecule. Molar mass = molecular weight in grams © 2006 Brooks/Cole - Thomson  8 Molecular & Ionic Compounds Heme NaCl N Fe © 2006 Brooks/Cole - Thomson  9 ELEMENTS THAT EXIST AS MOLECULES Allotropes of C © 2006 Brooks/Cole - Thomson  10 ELEMENTS THAT EXIST AS DIATOMIC MOLECULES © 2006 Brooks/Cole - Thomson  11 ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES S8 sulfur molecules White P4 and polymeric red phosphorus © 2006 Brooks/Cole - Thomson  12 IONS AND IONIC COMPOUNDS see Screen 3.5 IONS are atoms or groups of atoms with a positive or negative charge. Taking away an electron from an atom gives a CATION with a positive charge Adding an electron to an atom gives an ANION with a negative charge. © 2006 Brooks/Cole - Thomson  13 Forming Cations & Anions A CATION forms An ANION forms when an atom when an atom loses one or gains one or more electrons. more electrons © 2006 Brooks/Cole - Thomson  14 Forming Cations & Anions Active figure 3.5 © 2006 Brooks/Cole - Thomson  15 PREDICTING ION CHARGES In general metals (Mg) lose electrons ---> cations nonmetals (F) gain electrons ---> anions © 2006 Brooks/Cole - Thomson  16 Charges on Common Ions -4 -3 -2 -1 +1 +2 +3 By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom. © 2006 Brooks/Cole - Thomson  17 Predicting Charges on Monatomic Ions © 2006 Brooks/Cole - Thomson  18 METALS M ---> n e- + Mn+ where n = periodic group Na+ sodium ion Mg2+ magnesium ion Al3+ aluminum ion Transition metals --> M2+ or M3+ are common Fe2+ iron(II) ion Fe3+ iron(III) ion © 2006 Brooks/Cole - Thomson  19 NONMETALS NONMETAL + n e- ------> Xn- where n = 8 - Group no. Group 4A Group 5A Group 6A Group 7A C4-,carbide N3-, nitride O2-, oxide F-, fluoride S2-, sulfide Cl-, chloride Name derived Br-, bromide by adding -ide to stem I-, iodide © 2006 Brooks/Cole - Thomson  20 POLYATOMIC IONS Groups of atoms with a charge. MEMORIZE the names and formulas in Table 3.1, page 107. © 2006 Brooks/Cole - Thomson  21 Note: many O containing anions have names ending in –ate (or -ite). © 2006 Brooks/Cole - Thomson  22 Polyatomic Ions HNO3 NO3- nitric acid nitrate ion © 2006 Brooks/Cole - Thomson  23 Polyatomic Ions NH4+ ammonium ion One of the few common polyatomic cations © 2006 Brooks/Cole - Thomson  24 Polyatomic Ions PO43- phosphate ion CH3CO2- acetate ion © 2006 Brooks/Cole - Thomson  25 Polyatomic Ions NO3- nitrate ion NO2- nitrite ion © 2006 Brooks/Cole - Thomson  COMPOUNDS 26 FORMED FROM IONS CATION + ANION ---> COMPOUND Na+ + Cl- --> NaCl A neutral compd. requires equal number of + and - charges. © 2006 Brooks/Cole - Thomson  27 IONIC COMPOUNDS NH4 + Cl - ammonium chloride, NH4Cl © 2006 Brooks/Cole - Thomson  28 Some Ionic Compounds Ca2+ + 2 F- ---> CaF2 Mg2+ + NO3- ----> Mg(NO3)2 magnesium nitrate Fe2+ + PO43- ----> calcium fluoride Fe3(PO4)2 iron(II) phosphate © 2006 Brooks/Cole - Thomson  Properties of Ionic Compounds 29 Forming NaCl from Na and Cl2 A metal atom can transfer an electron to a nonmetal. The resulting cation and anion are attracted to each other by electrostatic forces. © 2006 Brooks/Cole - Thomson  30 Electrostatic Forces The oppositely charged ions in ionic compounds are attracted to one another by ELECTROSTATIC FORCES. These forces are governed by COULOMB’S LAW. © 2006 Brooks/Cole - Thomson  31 Electrostatic Forces COULOMB’S LAW As ion charge increases, the attractive force _______________. As the distance between ions increases, the attractive force ________________. This idea is important and will come up many times in future discussions! © 2006 Brooks/Cole - Thomson  32 Electrostatic Forces COULOMB’S LAW Active Figure 3.10 © 2006 Brooks/Cole - Thomson  33 Importance of Coulomb’s Law NaCl, Na+ and Cl-, MgO, Mg2+ and O2- m.p. 804 oC m.p. 2800 oC © 2006 Brooks/Cole - Thomson  34 Molecular Compounds Compounds without Ions CO2 Carbon dioxide CH4 methane BCl3 boron trichloride © 2006 Brooks/Cole - Thomson  35 Naming Molecular Compounds All are formed from CO2 Carbon dioxide two or more nonmetals. Ionic compounds generally involve a metal BCl3 CH4 methane boron trichloride and nonmetal (NaCl) © 2006 Brooks/Cole - Thomson  36 Empirical & Molecular Formulas A pure compound always consists of the same elements combined in the same proportions by weight. Therefore, we can express molecular composition as PERCENT BY WEIGHT Ethanol, C2H6O 52.13% C 13.15% H 34.72% O © 2006 Brooks/Cole - Thomson  37 Percent Composition Consider some of the family of nitrogen- oxygen compounds: NO2, nitrogen dioxide and closely related, NO, nitrogen monoxide (or nitric oxide) Chemistry of NO, nitrogen monoxide Structure of NO2 © 2006 Brooks/Cole - Thomson  38 Percent Composition Consider NO2, Molar mass = ? What is the weight percent of N and of O? 14.0 g N Wt. % N = 100% = 30.4 % 46.0 g NO2 Wt. % O = 2 (16.0 g O per mole ) x 100 % = 69.6% 46.0 g What are the weight percentages of N and O in NO? © 2006 Brooks/Cole - Thomson  39 How to Determine a Formula? Mass spectrometer © 2006 Brooks/Cole - Thomson  40 Mass Spectrum of Ethanol Mass Spectrum of Ethanol (from the NIST site) CH2O+ 31 CH3CH2O+ 45 CH3CH2OH+ 46 © 2006 Brooks/Cole - Thomson  41 Determining Formulas In chemical analysis we determine the % by weight of each element in a given amount of pure compound and derive the EMPIRICAL or SIMPLEST formula. PROBLEM: A compound of B and H is 81.10% B. What is its empirical formula? © 2006 Brooks/Cole - Thomson  42 A compound of B and H is 81.10% B. Its empirical formula is B2H5. What is its molecular formula? Is the molecular formula B2H5, B4H10, B6H15, B8H20, etc.? B 2H 6 B2H6 is one example of this class of compounds. © 2006 Brooks/Cole - Thomson  43 A compound of B and H is 81.10% B. Its empirical formula is B2H5. What is its molecular formula? We need to do an EXPERIMENT to find the MOLAR MASS. Here experiment gives 53.3 g/mol Compare with the mass of B2H5 = 26.66 g/unit Find the ratio of these masses. 53.3 g/mol 2 units of B2H5 = 26.66 g/unit of B2H5 1 mol Molecular formula = B4H10 © 2006 Brooks/Cole - Thomson  44 DETERMINE THE FORMULA OF A COMPOUND OF Sn AND I Sn(s) + some I2(s) ---> SnIx © 2006 Brooks/Cole - Thomson  45 Data to Determine the formula of a Sn—I Compound Reaction of Sn and I2 is done using excess Sn. Mass of Sn in the beginning = 1.056 g Mass of iodine (I2) used = 1.947 g Mass of Sn remaining = 0.601 g See p. 125 © 2006 Brooks/Cole - Thomson