Chapter 5 Molecules and Compounds

2 Molecules and Compounds Salt Sodium – shiny, reactive, poisonous Chlorine – pale yellow gas, reactive, poisonous Sodium chloride – table salt Sugar Carbon – pencil or diamonds Hydrogen – flammable gas Oxygen – a gas in air Combine to form white crystalline sugar

3 Law of Constant Composition all pure substances have constant composition all samples of a pure substance contain the same elements in the same percentages (ratios) mixtures have variable composition If we decompose water by electrolysis, we find 16.0 grams of oxygen to every 2.00 grams of hydrogen. Water has a constant Mass Ratio of Oxygen to Hydrogen of 8.0.

4 Why do Compounds Show Constant Composition smallest piece of a compound is called a molecule every molecule of a compound has the same number and type of atoms as determined by the electronic structures of the atoms (more on that later in the year) since all the molecules of a compound are identical… every sample will have the same ratio of the elements every sample of the compound will have the same properties

5 Two samples of carbon dioxide, obtained from different sources, were decomposed into their constituent elements. One sample produced 4.8 g of oxygen and 1.8 g of carbon, and the other sample produced 17.1 g of oxygen and 6.4 g of carbon. Show that these results are consistent with the law of constant composition. EXAMPLE 5.1 Constant Composition of Compounds To show this, compute the mass ratio of one element to the other by dividing the larger mass by the smaller one. For the first sample: For the second sample: Solution: Since the ratios are the same for the two samples, these results are consistent with the law of constant composition. Example; Constant Composition

A What is the carbon-hydrogen mass ratio for methane (CH 4 )? B If the mass ratio of lead(II) sulfide is g lead and 41.8 g sulfur, how much lead is required to completely react with 85.6 g of sulfur? Examples; Using Mass Ratios

7 Formulas Describe Compounds water = H 2 O  two atoms of hydrogen and 1 atom of oxygen table sugar = C 12 H 22 O 11  12 atoms of C, 22 atoms of H and 11 atoms O

8 Order of Elements in a Formula metals written first NaCl nonmetals written in order from Table 5.1 CO 2 are occasional exceptions for historical or informational reasons  H 2 O, but NaOH Table 5.1 Order of Listing Nonmetals in Chemical Formulas CPNHSIBrClOF

9 Molecules with Polyatomic Ions Mg(NO 3 ) 2 compound called magnesium nitrate symbol of the polyatomic ion called nitrate symbol of the polyatomic ion called sulfate CaSO 4 compound called calcium sulfate implied “1” subscript on magnesium implied “1” subscript on calcium parentheses to group two NO 3 ’sno parentheses for one SO 4

10 Molecules with Polyatomic Ions Mg(NO 3 ) 2 compound called magnesium nitrate CaSO 4 compound called calcium sulfate subscript indicating two NO 3 groups no subscript indicating one SO 4 group implied “1” subscript on nitrogen, total 2 N implied “1” subscript on sulfur, total 1 S stated “3” subscript on oxygen, total 6 O stated “4” subscript on oxygen, total 4 O

11 Classifying Materials atomic elements = elements whose particles are single atoms molecular elements = elements whose particles are multi-atom molecules molecular compounds = compounds whose particles are molecules made of only nonmetals ionic compounds = compounds whose particles are cations and anions

12 Molecular Elements Certain elements occur as 2 atom molecules Rule of 7’s there are 7 common diatomic elements find the element with atomic number 7, N make a figure 7 by going over to Group 7A, then down don’t forget to include H 2 H2H2 Cl 2 Br 2 I2I2 7 VIIA N 2 O 2 F 2 P4P4 S8S8

13 Molecular Compounds two or more nonmetals smallest unit is a molecule

14 Ionic Compounds metals + nonmetals no individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units

15 Molecular View of Elements and Compounds

16 Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound aluminum, Al aluminum chloride, AlCl 3 chlorine, Cl 2 acetone, C 3 H 6 O carbon monoxide, CO cobalt, Co

17 Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound aluminum, Al = atomic element aluminum chloride, AlCl 3 = ionic compound chlorine, Cl 2 = molecular element acetone, C 3 H 6 O = molecular compound carbon monoxide, CO = molecular compound cobalt, Co = atomic element

Formula-to-Name Step 1 Is the compound one of the exceptions to the rules? H 2 O = water, steam, ice NH 3 = ammonia

Formula-to-Name Step 2 What major class of compound is it? Ionic or Molecular

20 Major Classes Ionic metal + nonmetal  metal first in formula  Binary Ionic compounds with polyatomic ions Molecular 2 nonmetals  Binary Molecular (or Binary Covalent) Acids – formula starts with H  though acids are molecular, they behave as ionic when dissolved in water  may be binary or oxyacid

Formula-to-Name Step 3 What major subclass of compound is it? Binary Ionic, Ionic with Polyatomic Ions, Binary Molecular, Binary Acid, Oxyacid

22 Classifying Compounds Compounds containing a metal and a nonmetal = binary ionic Type I and II Compounds containing a polyatomic ion = ionic with polyatomic ion Compounds containing two nonmetals = binary molecular compounds Compounds containing H and a nonmetal = binary acids Compounds containing H and a polyatomic ion = oxyacids

Formula-to-Name Step 4 Apply Rules for the Class and Subclass

24 Formula-to-Name Rules for Ionic Made of cation and anion Name by simply naming the ions If cation is:  Type I metal = metal name  Type II metal = metal name(charge)  Polyatomic ion = name of polyatomic ion If anion is:  Nonmetal = stem of nonmetal name + ide  Polyatomic ion = name of polyatomic ion

25 Monatomic Nonmetal Anion determine the charge from position on the Periodic Table to name anion, change ending on the element name to –ide 4A = -45A = -36A = -27A = -1 C = carbideN = nitrideO = oxideF = fluoride Si = silicideP = phosphideS = sulfideCl = chloride

26 Metal Cations Type I metals whose ions can only have one possible charge  IA, IIA, (Al, Ga, In) determine charge by position on the Periodic Table  IA = +1, IIA = +2, (Al, Ga, In = +3) Type II metals whose ions can have more than one possible charge determine charge by charge on anion How do you know a metal cation is Type II? its not Type I !!!

27 Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms. lithium, Li copper, Cu gallium, Ga tin, Sn strontium, Sr

28 Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms. lithium, LiType I+1 copper, CuType II gallium, GaType I+3 tin, SnType II strontium, SrType I+2

29 Type I Binary Ionic Compounds Contain Metal Cation + Nonmetal Anion Metal listed first in formula & name 1.name metal cation first, name nonmetal anion second 2.cation name is the metal name 3.nonmetal anion named by changing the ending on the nonmetal name to -ide

30 Type II Binary Ionic Compounds Contain Metal Cation + Nonmetal Anion Metal listed first in formula & name 1.name metal cation first, name nonmetal anion second 2.metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge determine charge from anion charge Common Type II cations in Table nonmetal anion named by changing the ending on the nonmetal name to -ide

31 Examples LiCl = lithium chloride AlCl 3 = aluminum chloride PbO = lead(II) oxide PbO 2 = lead(IV) oxide Mn 2 O 3 = manganese(III) oxide ZnCl 2 = zinc(II) chloride or zinc chloride AgCl = silver(I) chloride or silver chloride

32 Compounds Containing Polyatomic Ions Polyatomic ions are single ions that contain more than one atom Name any ionic compound by naming cation first and then anion Non-polyatomic cations named like Type I and II Non-polyatomic anions named with -ide

33 Li +1 Na +1 K +1 Rb +1 Cs +1 Be +2 Mg +2 Ca +2 Sr +2 Ba +2 Al +3 Ga +3 In +3 O -2 S -2 Se -2 Te -2 F -1 Cl -1 Br -1 I -1 N -3 P -3 As -3 IA IIAIIIA VIIA VIA VA Zn +2 Cd +2 Ag +1 Fixed Charge Metals and Nonmetals

34 Some Common Polyatomic Ions NameFormula acetateC2H3O2–C2H3O2– carbonateCO 3 2– hydrogen carbonate (aka bicarbonate) HCO 3 – hydroxideOH – nitrateNO 3 – nitriteNO 2 – chromateCrO 4 2– dichromateCr 2 O 7 2– ammoniumNH 4 + NameFormula hypochloriteClO – chloriteClO 2 – chlorateClO 3 – perchlorateClO 4 – sulfateSO 4 2– sulfiteSO 3 2– hydrogensulfate (aka bisulfate) HSO 4 – hydrogensulfite (aka bisulfite) HSO 3 –

35 Patterns for Polyatomic Ions 1.elements in the same column form similar polyatomic ions same number of O’s and same charge ClO 3 - = chlorate  BrO 3 - = bromate 2.if the polyatomic ion starts with H, the name adds hydrogen- prefix before name and add 1 to the charge CO 3 2- = carbonate  HCO 3 -1 = hydrogencarbonate

36 Periodic Pattern of Polyatomic Ions -ate groups BO 3 -3 NO 3 SiO 3 -2 PO 4 -3 SO 4 -2 ClO 3 AsO 4 -3 SeO 4 -2 BrO 3 TeO 4 -2 IO 3 CO 3 -2 IIIAIVA VA VIA VIIA

37 Binary Molecular Compounds of 2 Nonmetals 1.Name first element in formula first use the full name of the element 2.Name the second element in the formula with an -ide as if it were an anion, however, remember these compounds do not contain ions! 3.Use a prefix in front of each name to indicate the number of atoms a)Never use the prefix mono- on the first element

38 Subscript - Prefixes 1 = mono - not used on first nonmetal 2 = di- 3 = tri- 4 = tetra- 5 = penta- 6 = hexa- 7 = hepta- 8 = octa- 9 = nona- 10 = deca- drop last “a” if name begins with vowel

39 Acids Contain H +1 cation and anion in aqueous solution Binary acids have H +1 cation and nonmetal anion Oxyacids have H +1 cation and polyatomic anion

40 Formula-to-Name Acids acids are molecular compounds that often behave like they are made of ions All names have acid at end Binary Acids = hydro prefix + stem of the name of the nonmetal + ic suffix Oxyacids if polyatomic ion ends in –ate = name of polyatomic ion with –ic suffix if polyatomic ion ends in –ite = name of polyatomic ion with –ous suffix

41 Example – Naming Binary Acids HCl 1.Is it one of the common exceptions? H 2 O, NH 3, CH 4, NaCl, C 12 H 22 O 11 = No! 2.Identify Major Class first element listed is H,  Acid 3.Identify the Subclass 2 elements,  Binary Acid

42 Sample - Naming Binary Acids – HCl 4.Identify the anion Cl = Cl -, chloride because Group 7A 5.Name the anion with an –ic suffix Cl - = chloride  chloric 6.Add a hydro- prefix to the anion name hydrochloric 7.Add the word acid to the end hydrochloric acid

43 Example – Naming Oxyacids H 2 SO 4 1.Is it one of the common exceptions? H 2 O, NH 3, CH 4, NaCl, C 12 H 22 O 11 = No! 2.Identify Major Class first element listed is H,  Acid 3.Identify the Subclass 3 elements in the formula,  Oxyacid

44 Example – Naming Oxyacids H 2 SO 4 4.Identify the anion SO 4 = SO 4 2- = sulfate 5.If the anion has –ate suffix, change it to –ic. If the anion has –ite suffix, change it to -ous SO 4 2- = sulfate  sulfuric 6.Write the name of the anion followed by the word acid sulfuric acid (kind of an exception, to make it sound nicer!)

45 Example – Naming Oxyacids H 2 SO 3 1.Is it one of the common exceptions? H 2 O, NH 3, CH 4, NaCl, C 12 H 22 O 11 = No! 2.Identify Major Class first element listed is H,  Acid 3.Identify the Subclass 3 elements in the formula,  Oxyacid

46 Example – Naming Oxyacids H 2 SO 3 4.Identify the anion SO 3 = SO 3 2- = sulfite 5.If the anion has –ate suffix, change it to –ic. If the anion has –ite suffix, change it to -ous SO 3 2- = sulfite  sulfurous 6.Write the name of the anion followed by the word acid sulfurous acid

47 Formula-to-Name Flow Chart

Name – to – Formula

49 Writing the Formulas from the Names For binary molecular compounds, use the prefixes to determine the subscripts For Type I, Type II, Ternary Compounds and Acids 1.Determine the ions present 2.Determine the charges on the cation and anion 3.Balance the charges to get the subscripts

50 Example – Binary Molecular dinitrogen pentoxide Identify the symbols of the elements nitrogen = N oxide = oxygen = O Write the formula using prefix number for subscript di = 2, penta = 5 N 2 O 5

51 Compounds that Contain Ions compounds of metals with nonmetals are made of ions metal atoms form cations, nonmetal atoms for anions compound must have no total charge, therefore we must balance the numbers of cations and anions in a compound to get 0 charge if Na + is combined with S 2-, you will need 2 Na + ions for every S 2- ion to balance the charges, therefore the formula must be Na 2 S

52 Writing Formulas for Ionic Compounds 1.Write the symbol for the metal cation and its charge 2.Write the symbol for the nonmetal anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the sum of the charges of the cation cancels the sum of the anions

53 Write the formula of a compound made from aluminum ions and oxide ions 1.Write the symbol for the metal cation and its charge 2.Write the symbol for the nonmetal anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions Al +3 column IIIA O 2- column VIA Al +3 O 2- Al 2 O 3 Al = (2)∙(+3) = +6 O = (3)∙(-2) = -6

54 Practice - What are the formulas for compounds made from the following ions? potassium ion with a nitride ion calcium ion with a bromide ion aluminum ion with a sulfide ion

55 Practice - What are the formulas for compounds made from the following ions? K + with N 3- K 3 N Ca +2 with Br - CaBr 2 Al +3 with S 2- Al 2 S 3

56 Example – Ionic Compounds manganese(IV) sulfide 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions Mn +4 S 2- Mn +4 S 2- Mn 2 S 4 Mn = (1)∙(+4) = +4 S = (2)∙(-2) = -4 MnS 2

57 Example – Ionic Compounds Iron(III) phosphate 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions Fe +3 PO 4 3- Fe +3 PO 4 3- Fe 3 (PO 4 ) 3 Fe = (1)∙(+3) = +3 PO 4 = (1)∙(-3) = -3 FePO 4

58 Example – Ionic Compounds ammonium carbonate 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions NH 4 + CO 3 2- NH 4 + CO 3 2- (NH 4 ) 2 CO 3 NH 4 = (2)∙(+1) = +2 CO 3 = (1)∙(-2) = -2 (NH 4 ) 2 CO 3

59 Practice - What are the formulas for compounds made from the following ions? copper(II) ion with a nitride ion iron(III) ion with a bromide ion aluminum ion with a sulfate ion

60 Practice - What are the formulas for compounds made from the following ions? Cu 2+ with N 3- Cu 3 N 2 Fe +3 with Br - FeBr 3 Al +3 with SO 4 2- Al 2 (SO 4 ) 3

61 Example – Binary Acids hydrosulfuric acid 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions H+H+ S 2- H + S 2- H2SH2S H = (2)∙(+1) = +2 S = (1)∙(-2) = -2 H2SH2S in all acids the cation is H + hydro means binary

62 Example – Oxyacids carbonic acid 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Charge (without sign) becomes subscript for other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions H+H+ CO 3 2- H + CO 3 2- H 2 CO 3 H = (2)∙(+1) = +2 CO 3 = (1)∙(-2) = -2 H 2 CO 3 in all acids the cation is H + no hydro means polyatomic ion -ic means -ate ion

63 Practice - What are the formulas for the following acids? chlorous acid phosphoric acid hydrobromic acid

64 Practice - What are the formulas for the following acids? H + with ClO 2 – HClO 2 H + with PO 4 3– H 3 PO 4 H + with Br – HBr

65 Formula Mass the mass of an individual molecule or formula unit also known as molecular mass or molecular weight sum of the masses of the atoms in a single molecule or formula unit whole = sum of the parts! mass of 1 molecule of H 2 O = 2(1.01 amu H) amu O = amu