1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 3 Molecules, Ions and Their Compounds © 2006 Brooks/Cole Thomson Lectures written by John Kotz

2 © 2006 Brooks/Cole - Thomson Molecules, Ions & Their Compounds NaCl, salt Buckyball, C 60 Ethanol, C 2 H 6 O

3 © 2006 Brooks/Cole - Thomson Compounds & Molecules COMPOUNDS are a combination of 2 or more elements in definite ratios by mass.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.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.MOLECULES are the smallest unit of a compound that retains the characteristics of the compound.

4 © 2006 Brooks/Cole - Thomson MOLECULAR FORMULAS Formula for glycine is C 2 H 5 NO 2Formula for glycine is C 2 H 5 NO 2 In one molecule there areIn one molecule there are –2 C atoms –5 H atoms –1 N atom –2 O atoms

5 © 2006 Brooks/Cole - Thomson WRITING FORMULAS Can also write glycine formula as –H 2 NCH 2 COOH to show atom ordering structural formulaor in the form of a structural formula

6 © 2006 Brooks/Cole - Thomson MOLECULAR MODELING Ball & stick Space-filling Structural formula of glycine

7 © 2006 Brooks/Cole - Thomson The molecule pictured here is one of the essential amino acids. What is the molecular formula of the acid?

8 © 2006 Brooks/Cole - Thomson MOLECULAR WEIGHT AND MOLAR MASS Molecular weight = sum of the atomic weights of all atoms in the molecule. Molar mass = molecular weight in grams

9 © 2006 Brooks/Cole - Thomson What is the molar mass of ethanol, C 2 H 6 O? 1 mol contains 2 mol C (12.01 g C/1 mol) = g C 6 mol H (1.01 g H/1 mol) = 6.06 g H 1 mol O (16.00 g O/1 mol) = g O TOTAL = molar mass = g/mol

10 © 2006 Brooks/Cole - Thomson Formula = Molar mass = TylenolTylenol C 8 H 9 NO g/mol

11 © 2006 Brooks/Cole - Thomson Molar Mass

12 © 2006 Brooks/Cole - Thomson How many moles of alcohol are there in a “standard” can of beer if there are 21.3 g of C 2 H 6 O? (a) Molar mass of C 2 H 6 O = g/mol (b) Calc. moles of alcohol

13 © 2006 Brooks/Cole - Thomson How many molecules of alcohol are there in a “standard” can of beer if there are 21.3 g of C 2 H 6 O? = 2.78 x molecules We know there are mol of C 2 H 6 O.

14 © 2006 Brooks/Cole - Thomson How many atoms of C are there in a “standard” can of beer if there are 21.3 g of C 2 H 6 O? = 5.57 x C atoms There are 2.78 x molecules. Each molecule contains 2 C atoms. Therefore, the number of C atoms is

15 © 2006 Brooks/Cole - Thomson Molecular & Ionic Compounds Heme NaCl Fe N

16 © 2006 Brooks/Cole - Thomson ELEMENTS THAT EXIST AS MOLECULES Allotropes of C

17 © 2006 Brooks/Cole - Thomson ELEMENTS THAT EXIST AS DIATOMIC MOLECULES

18 © 2006 Brooks/Cole - Thomson ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES White P 4 and polymeric red phosphorus S 8 sulfur molecules

19 © 2006 Brooks/Cole - Thomson IONS AND IONIC COMPOUNDS see Screen 3.5 IONS are atoms or groups of atoms with a positive or negative charge.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 chargeTaking 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.Adding an electron to an atom gives an ANION with a negative charge.

20 © 2006 Brooks/Cole - Thomson Forming Cations & Anions A CATION forms when an atom loses one or more electrons. An ANION forms when an atom gains one or more electrons Mg --> Mg e- F + e- --> F -

21 © 2006 Brooks/Cole - Thomson Active figure 3.5

22 © 2006 Brooks/Cole - Thomson PREDICTING ION CHARGES In general metals (Mg) lose electrons ---> cationsmetals (Mg) lose electrons ---> cations nonmetals (F) gain electrons ---> anionsnonmetals (F) gain electrons ---> anions See CD-ROM Screen 3.5 and book Figure 3.7See CD-ROM Screen 3.5 and book Figure 3.7

23 © 2006 Brooks/Cole - Thomson Charges on Common Ions By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.

24 © 2006 Brooks/Cole - Thomson Predicting Charges on Monatomic Ions

25 © 2006 Brooks/Cole - Thomson Which ion in the following list is NOT likely to form?

26 © 2006 Brooks/Cole - Thomson 1.25 protons and 25 electrons protons and 26 electrons protons and 24 electrons protons and 25 electrons protons and 26 electrons.

27 © 2006 Brooks/Cole - Thomson METALS M ---> n e- + M n+ where n = periodic group Na + sodium ion Mg 2+ magnesium ion Al 3+ aluminum ion Transition metals --> M 2+ or M 3+ are common Fe 2+ iron(II) ion Fe 3+ iron(III) ion

28 © 2006 Brooks/Cole - Thomson NONMETALSNONMETALS NONMETAL + n e > X n- where n = 8 - Group no. C 4-,carbide N 3-, nitride O 2-, oxide S 2-, sulfide F -, fluoride Cl -, chloride Group 7AGroup 6A Group 4A Group 5A Br -, bromide I -, iodide Name derived by adding -ide to stem

29 © 2006 Brooks/Cole - Thomson Ion Formation Reaction of aluminum and bromine

30 © 2006 Brooks/Cole - Thomson CATION + ANION ---> COMPOUND COMPOUND CATION + ANION ---> COMPOUND COMPOUND A neutral compd. requires equal number of + equal number of + and - charges. A neutral compd. requires equal number of + equal number of + and - charges. COMPOUNDS FORMED FROM IONS Na + + Cl - --> NaCl

31 © 2006 Brooks/Cole - Thomson IONIC COMPOUNDS NH 4 + Cl - ammonium chloride, NH 4 Cl

32 © 2006 Brooks/Cole - Thomson Some Ionic Compounds Mg 2+ + NO > Mg(NO 3 ) 2 magnesium nitrate Fe 2+ + PO > Fe 3 (PO 4 ) 2 iron(II) phosphate (See CD, Screen 3.11 for naming practice) calcium fluoride Ca F - ---> CaF 2

33 © 2006 Brooks/Cole - Thomson Properties of Ionic Compounds Forming NaCl from Na and Cl 2 A metal atom can transfer an electron to a nonmetal.A metal atom can transfer an electron to a nonmetal. The resulting cation and anion are attracted to each other by electrostatic forces.The resulting cation and anion are attracted to each other by electrostatic forces.

34 © 2006 Brooks/Cole - Thomson 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.

35 © 2006 Brooks/Cole - Thomson POLYATOMIC IONS CD Screen 3.6 Groups of atoms with a charge. MEMORIZE the names and formulas in Table 3.1, page 107.

36 © 2006 Brooks/Cole - Thomson Note: many O containing anions have names ending in –ate (or -ite).

37 © 2006 Brooks/Cole - Thomson Which compound in the following list is NOT possible?

38 © 2006 Brooks/Cole - Thomson Polyatomic Ions HNO 3 nitric acid NO 3 - nitrate ion

39 © 2006 Brooks/Cole - Thomson Polyatomic Ions NH 4 + ammonium ion One of the few common polyatomic cations

40 © 2006 Brooks/Cole - Thomson Polyatomic Ions CO 3 2- carbonate ion HCO 3 - bicarbonate ion hydrogen carbonate

41 © 2006 Brooks/Cole - Thomson PO 4 3- phosphate ion CH 3 CO 2 - acetate ion Polyatomic Ions

42 © 2006 Brooks/Cole - Thomson SO 4 2- sulfate ion SO 3 2- sulfite ion Polyatomic Ions

43 © 2006 Brooks/Cole - Thomson NO 3 - nitrate ion NO 2 - nitrite ion Polyatomic Ions

44 © 2006 Brooks/Cole - Thomson 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!

45 © 2006 Brooks/Cole - Thomson Electrostatic Forces COULOMB’S LAW Active Figure 3.10

46 © 2006 Brooks/Cole - Thomson Importance of Coulomb’s Law NaCl, Na + and Cl -, m.p. 804 o C MgO, Mg 2+ and O 2- m.p o C

47 © 2006 Brooks/Cole - Thomson Molecular Compounds Compounds without Ions CH 4 methane CO 2 Carbon dioxide BCl 3 boron trichloride

48 © 2006 Brooks/Cole - Thomson Naming Molecular Compounds CH 4 methane BCl 3 boron trichloride CO 2 Carbon dioxide All are formed from two or more nonmetals. Ionic compounds generally involve a metal and nonmetal (NaCl)

49 © 2006 Brooks/Cole - Thomson 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, C 2 H 6 O 52.13% C 13.15% H 34.72% O

50 © 2006 Brooks/Cole - Thomson Percent Composition Consider some of the family of nitrogen- oxygen compounds: NO 2, nitrogen dioxide and closely related, NO, nitrogen monoxide (or nitric oxide) Structure of NO 2 Chemistry of NO, nitrogen monoxide

51 © 2006 Brooks/Cole - Thomson Percent Composition Consider NO 2, Molar mass = ? What is the weight percent of N and of O? What are the weight percentages of N and O in NO?

52 © 2006 Brooks/Cole - Thomson How to Determine a Formula? Mass spectrometer

53 © 2006 Brooks/Cole - Thomson Mass Spectrum of Ethanol (from the NIST site) CH 3 CH 2 OH + CH 3 CH 2 O + 31 CH 2 O +

54 © 2006 Brooks/Cole - Thomson 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?

55 © 2006 Brooks/Cole - Thomson Because it contains only B and H, it must contain 18.90% H.Because it contains only B and H, it must contain 18.90% H. In g of the compound there are g of B and g of H.In g of the compound there are g of B and g of H. Calculate the number of moles of each constitutent.Calculate the number of moles of each constitutent. A compound of B and H is 81.10% B. What is its empirical formula?

56 © 2006 Brooks/Cole - Thomson Calculate the number of moles of each element in g of sample. A compound of B and H is 81.10% B. What is its empirical formula?

57 © 2006 Brooks/Cole - Thomson Now, recognize that atoms combine in the ratio of small whole numbers. 1 atom B + 3 atoms H --> 1 molecule BH 3 or 1 mol B atoms + 3 mol H atoms ---> 1 mol BH 3 molecules Find the ratio of moles of elements in the compound. A compound of B and H is 81.10% B. What is its empirical formula?

58 © 2006 Brooks/Cole - Thomson But we need a whole number ratio. 2.5 mol H/1.0 mol B = 5 mol H to 2 mol B EMPIRICAL FORMULA = B 2 H 5 Take the ratio of moles of B and H. Always divide by the smaller number. A compound of B and H is 81.10% B. What is its empirical formula?

59 © 2006 Brooks/Cole - Thomson A compound of B and H is 81.10% B. Its empirical formula is B 2 H 5. What is its molecular formula ? Is the molecular formula B 2 H 5, B 4 H 10, B 6 H 15, B 8 H 20, etc.? B 2 H 6 is one example of this class of compounds. B2H6B2H6

60 © 2006 Brooks/Cole - Thomson A compound of B and H is 81.10% B. Its empirical formula is B 2 H 5. 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 B 2 H 5 = g/unit = g/unit Find the ratio of these masses. Molecular formula = B 4 H 10

61 © 2006 Brooks/Cole - Thomson DETERMINE THE FORMULA OF A COMPOUND OF Sn AND I Sn(s) + some I 2 (s) ---> SnI x

62 © 2006 Brooks/Cole - Thomson Data to Determine the formula of a Sn—I Compound Reaction of Sn and I 2 is done using excess Sn.Reaction of Sn and I 2 is done using excess Sn. Mass of Sn in the beginning = gMass of Sn in the beginning = g Mass of iodine (I 2 ) used = gMass of iodine (I 2 ) used = g Mass of Sn remaining = gMass of Sn remaining = g See p. 125See p. 125

63 © 2006 Brooks/Cole - Thomson Find the mass of Sn that combined with g I 2. Mass of Sn initially = g Mass of Sn recovered = g Mass of Sn used = g Find moles of Sn used: Tin and Iodine Compound

64 © 2006 Brooks/Cole - Thomson Tin and Iodine Compound Now find the number of moles of I 2 that combined with 3.83 x mol Sn. Mass of I 2 used was g. How many mol of iodine atoms ? = x mol I atoms

65 © 2006 Brooks/Cole - Thomson Tin and Iodine Compound Now find the ratio of number of moles of moles of I and Sn that combined. Empirical formula is SnI 4