1. Molecules, Ions, and Their Compounds Goals: 1.Know formulas for ionic and molecular compounds. 2.Name compounds. 3.Understand some properties of ionic compounds. 4.Calculate and use molar mass. 5.Calculate % composition for a compound and derive formulas from experimental data.

2. What are compounds? What are molecules? COMPOUNDS are a combination of 2 or more elements in definite _____________. The character of each element is _________when forming a compound. MOLECULES are the smallest unit of a compound that retains the characteristics of the compound.

3. Compounds: Ionic and Molecular NaCl, salt CH 3 CH 2 OH, ethanol

4. What is a Molecular Formula? Molecular Formulas describe the composition of molecules: 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. Writing Molecular Formulas Can also write glycine formula as –H 2 NCH 2 COOH ( condensed formula ) to show atom ordering. or in the form of a structural formula:

6. Molecular Modeling Representations of glycine: Ball & stick Space-filling Write structural formula of glycine:

7. What is Molecular Weight? What is Molar Mass? Molecular weight: ______________ weights of all ________ in the molecule. Molar mass: molecular weight in ________.

8. What is the molar mass of ethanol, C 2 H 6 O?

9. Molar Mass Students should become familiar with calculations and use of molar mass.

10. 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? How many molecules ? How many C atoms ? 1. Calculate the number of moles : This is a grams to moles conversion. Need to know how many grams are there per mol of ethanol. 2. Calculate the number of molecules : 3. Calculate the number of C atoms : There are 2 C per ethanol molecule.

11. Compounds: Ionic and Molecular WaterCaffeine Citric acid NaCl

12. How to know? MgBr 2 CCl 4 K2SH2OK2SH2O CuSO 4 C 6 H 12 O 6 1. Most metal-containing compounds are ionic. 2. If there is no metal in the formula, it is likely that the compound is not ionic (except compounds from polyatomic ions based on nonmetals, ex: NH 4 NO 3 ). Learn the formulas of polyatomic ions.

13. What are Ions? How are Ions formed? 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.

14. Forming Ions

15. Predicting Ions Charges Look at Fig. 3.7 (page 105). In general, Metals (Li) loose electrons to become CATIONS. Nonmetals (F) gain electrons to become ANIONS.

16. +3 -4-2-3 +1 +2 By losing or gaining e-, the atom has the same number of e-’s as nearest Group 8A atom. Charges on Common Ions

17. Charges on Monoatomic Ions Students should become familiar with the charges of common ions.

18. Metals and their Ions M ---> n e- + M n+ where n = periodic group Na – Group 1Na + sodium ion Mg – Group 2Mg 2+ magnesium ion Al – Group 3Al 3+ aluminum ion Transition metals --> M 2+ or M 3+ are common Fe 2+ iron(II) ion Fe 3+ iron(III) ion

19. Nonmetals and their Ions 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 of monoatomic anion is derived by adding -ide to stem

20. Polyatomic Ions Groups of atoms with a charge.Groups of atoms with a charge. MEMORIZE the names and formulas in Table 3.1, page 107.MEMORIZE the names and formulas in Table 3.1, page 107. Students should become familiar with formulas, names, and charges of polyatomic ions.

21. Polyatomic Ions Note: many O containing anions have names ending in –ate (or -ite).

22. Naming Polyatomic Ions NH 4 + ammonium ion One of the few common polyatomic cations

23. Compounds formed from Ions CATION + ANION ---> COMPOUND COMPOUND CATION + ANION ---> COMPOUND COMPOUND A neutral compound requires equal number of + and - charges. A neutral compound requires equal number of + and - charges. Na + + Cl - --> NaCl +1 + (-1) = 0

24. What are Ionic Compounds? Ionic compounds are composed of ions. NH 4 + Cl - ammonium chloride, NH 4 Cl Students should become familiar with formulas and names ionic compounds.

25. Formation of Ionic Compounds Mg 2+ + NO 3 - ----> Mg(NO 3 ) 2 magnesium nitrate Fe 2+ + PO 4 3- ----> Fe 3 (PO 4 ) 2 iron(II) phosphate calcium fluoride Ca 2+ + 2 F - ---> CaF 2

26. Formation of Ionic Compounds A metal atom transfers an electron to a nonmetal.A metal atom transfers 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.

27. Formation of Ionic Compounds The oppositely charged ions in ionic compounds are attracted to one another by ELECTROSTATIC FORCES. These forces are governed by COULOMB’S LAW.

28. Electrostatic Forces and Ionic Compounds What happens to the attractive force when the charge on the ion increases?What happens to the attractive force when the charge on the ion increases? What happens to the attractive force when the distance between ions increases?What happens to the attractive force when the distance between ions increases?

29. Electrostatic Forces Coulomb’s Law

30. Importance of Coulomb’s Law. Why is the m.p. of MgO higher than that of NaCl? NaCl, Na + and Cl -, m.p. 804 o C MgO, Mg 2+ and O 2- m.p. 2800 o C

31. Melting Point Melting point is the temperature at which a substance goes from solid to liquid. In a solid: particles are fixed, in ionic solid they are fixed by very strong electrostatic attractions. In a liquid: particles move. In order to change the substance from solid to liquid (get the particles moving) the particles need some energy: just enough to break the electrostatic attractions. The stronger the attraction, the more energy is needed to overcome it: a higher melting point results.

32. Practice Select the compound with the higher melting point: NaCl, AlN KCl, CsI

33. Some general properties The compound is ionic: –The compound would conduct electricity if molten. –The compound dissolved in water it would be a strong electrolyte (produce plenty of ions). –The compound would be expected to be a solid at room temperature and pressure. –The compound would be expected to have a relatively high melting point. The compound is molecular: –If the compound dissolved in water it would be a non-electrolyte. –The compound would be expected to have a relatively low melting point.

34. Elements that exist as Molecules Allotropes of Carbon C 60 CC

35. Elements that exist as Diatomic Molecules

36. Elements that exist as Polyatomic Molecules White P 4 and polymeric red phosphorus S 8 sulfur molecules

37. What are Molecular Compounds? Compounds without ions. Methane, CH 4 Carbon dioxide, CO 2 Boron trichloride, BCl 3 Molecular compounds are formed from two or more nonmetals. Molecular compounds are formed from two or more nonmetals. Students should become familiar with formulas and names of molecular compounds.

38. Practice Which of the following are ionic, and which are molecular? Give their name. NaI CCl 4 Ca(NO 3 ) 2 FeCl 3 NF 3 NH 4 CH 3 COO NaBr 3

39. Empirical and 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

40. Mass percent Expression of molecular composition in terms of the mass of each element in the compound relative to the total mass of the compound. NO 2 Mass % N in NO 2 = Mass of N in 1 mol NO 2 Mass of 1 mol NO 2

41. Percent Composition Consider some of the family of nitrogen-oxygen compounds: NO 2, nitrogen dioxide and closely related, NO, nitrogen monoxide (or nitric oxide). What is the weight percent of N and of O in NO 2 ? In NO? Students should become familiar with calculations of % weight, empirical and molecular formulas.

42. What is the weight percent of N and of O in NO 2 ? In NO?

43. How can Molecular Formulas be determined? Molecular formulas can be determined from chemical analysis or instrumental methods, such as mass spectrometry. 46 45 CH 3 CH 2 OH + CH 3 CH 2 O + 31 CH 2 O +

44. 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. Benzene -Aromatic compound C6H6C6H6C6H6C6H6 CH

45. A compound of B and H is 81.10% B. What is its empirical formula? Because it contains only B and H, it must contain 18.90% H. In 100.0 g of the compound there are 81.10 g of B and 18.90 g of H. 1. Calculate the number of moles of each constituent in 100 g of sample.

46. A compound of B and H is 81.10% B. What is its empirical formula? 2. Find the ratio of moles of elements in the compound. Take the ratio of moles of B and H. Always divide by the smallest number. Find a whole number ratio.

47. Deriving Formulas Steps from % composition to formula: % A % B g A g B X mol A X mol B Convert weight percent to mass Convert mass to moles Find mole ratio x mol A y mol B Always divide the larger number by the smaller one. Ratio gives formula AxByAxByAxByAxBy

48. 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 = 26.66 g/unit 1. Find the ratio of these masses.

49. Determine the MOLECULAR Formula from Combining Masses (see page 125). Sn(s) + some I 2 (s) ---> SnI x Reaction of Sn and I 2 is done using excess Sn. Mass of Sn in the beginning = 1.056 g Mass of iodine (I 2 ) used = 1.947 g Mass of Sn remaining = 0.601 g

50. Tin and Iodine Compound 1. Find the mass of Sn (used in excess) that combined with 1.947 g I 2 (limiting reactant). 2. Find moles of Sn used:

51. 3. Now find the number of moles of I 2 that combined with the mol Sn. Mass of I 2 used was 1.947 g. 4. Calculate the mol of Iodine atoms: 5. Find the ratio of the number of moles of I and S that combined.

52. What are Hydrated Compounds? Hydrated compounds are those in which molecules of water are associated with the ions of the compound. CoCl 2 6H 2 OCoCl 2 Anhydride.

53. Hydrated Compounds Atoms in formula of compound: CoCl 2 6H 2 O.

54. Practice Ten grams of each substance contains the largest number of moles? H 2 OKrBaCl 2 H 2 OBr 2. Using molar masses, calculate number of moles. Know that the larger the molar mass, the fewer number of moles.

55. Practice How many nitrate ions are found in 1.50 moles of calcium nitrate? Particles in a mole? Avogadro’s number

56. Remember Go over all the contents of your textbook. Practice with examples and with problems at the end of the chapter. Practice with OWL tutor. Practice with the quiz on CD of Chemistry Now. Work on your assignment for Chapter 3.