Molecules, Compounds, and Chemical Equations

1
Molecules, Compounds, and Chemical Equations

• Chapter 3

2
Compounds may be ionic or molecular

• IONIC COMPOUNDS
• generally form between metals and nonmetals
• held together by attraction of oppositely
  charged ions
• MOLECULAR COMPOUNDS
• generally form between nonmetals
• held together by covalent chemical bonds

3
Elements compounds
4
Most elements are atomic, but a few are molecular
5
Some compounds are ionic

• An ionic compound (salt) is made of ions held
  together by electrostatic forces of attraction
• Positively charged ions are called cations
• Negatively charged ions are called anions
• The basic unit of a salt is a formula unit
• A formula unit is not a molecule, but the
  simplest ratio of cations anions in the lattice

6
Sodium Chloridean ionic compound
7
Some substances are molecular

• A molecular substance (element or compound) is
  made of molecules (atoms joined by covalent
  bonds)
• The basic unit of a molecular substance is a
  molecule

8
Molecular and ionic
9
Acetic acid contains 2 C, 2 O, and 4 H

• Empirical formula CH2O
• the simplest ratio of atoms
• Molecular formula C2H4O2
• the actual number of atoms
• Structural formula
• shows arrangement of atoms CH3COH

O

10
Mass Percent Composition

• The mass of one element in a compound divided by
  the total mass of the compound, times 100

11
Mass Percent Composition

• Calculate the mass percent composition of acetic
  acid, HC2H3O2

12
Empirical Formula from Percent Composition

• Use masses given, or assume you have 100 g of
  compound, so mass of each element the percent
  given for each
• Convert the mass of each element into moles
• Write a tentative formula based on the moles
  calculated for each element
• Divide all subscripts by the smallest value to
  convert them to small whole numbers

13
Calculating an Empirical Formula

• Analysis of a sample of a brown gas which is an
  important air pollutant shows that it contains
  2.34 g of nitrogen and 5.34 g of oxygen. What is
  the empirical formula of the gas?

14
Calculating an Empirical Formula

• Analysis of a sample of a brown gas which is an
  important air pollutant shows that it is 30.47
  nitrogen and 69.53 oxygen by mass. What is the
  empirical formula of the gas?
• 30.47 g N x 1 mol 2.175 mol N
  14.0067 g
• 69.53 g O x 1 mol 4.346 mol O
  15.9994 g
• N2.175O4.346 N(2.175/2.175)O(4.3462.175) N1.000O
  1.998
• Empirical formula is NO2

15
Finding the Molecular Formula from the Empirical
Formula

• Molecular formula actual number of atoms
  combined in the molecule
• Find ratio true molar mass
  empirical molar mass
• Multiply subscripts in empirical formula by ratio
• empirical formula is CH true molar mass is 78
  g/mol
• 78 g/mol 6
• (12 1) g/mol
• Molecular formula C6H6

16
Molecular Formulas

• A compound has the empirical formula of NO2. Its
  molar mass is determined to be about 92 g/mol.
  What is the compounds molecular formula?
• The empirical formula mass is 14 2(16) 46
  g/mol
• 92 g/mol 2 46 g/mol
• Molecular formula is N2O4

17
Empirical and Molecular FormulasExamples 3-5A
and 3-5B

• Diacetone glucose has a molecular mass of 260 amu
  and this composition 55.37 C, 7.75 H, and
  36.88 O. What are the empirical and molecular
  formulas of this substance?
• Sorbitol has a molecular mass of 182 amu andthis
  composition 39.56 C, 7.74 H, and 52.70 O.
  What are the empirical and molecular formulas of
  sorbitol?

18
Determining a Formula using Combustion Analysis
19
Tracking C and H atoms
20
(No Transcript)
21
Combustion Analysis

• 0.1000 g of a C, H, and O compound is burned in
  O2 to yield 0.1953 g CO2 and 0.1000 g H2O
• In a separate experiment, the molar mass is
  determined to be about 90 g/mol
• Calculate
• composition
• Empirical formula
• Molecular formula

22
Combustion Analysis

• 0.1953 g CO2 x 1 mol CO2 x 1 mol C
  44.0098 g CO2 1 mol CO2
  0.004438 mol C x 12.011 g C 0.05330 g
  C 1 mol C
• 0.1000 g H2O x 1 mol H2O x 2 mol H
  18.0153 g H2O 1 mol
  H2O 0.01110 mol H x 1.00794 g H
  0.01119 g H 1 mol H

23
Combustion Analysis

• 0.1000 g of the compound contains 0.05330 g
  C 0.01119 g H 0.06449 g C H
• The rest of the compound is oxygen 0.1000 g
  compound 0.06449 g CH 0.03551 g O x 1
  mol 0.002219 mol O 15.9994 g

24
Combustion Analysis composition

• 0.1000 g of the compound contains 0.05330 g C,
  0.01119 g H, and 0.03551 g O
• C 0.05330 g C x 100 53.30 C
  0.1000g
• H 0.01119 g H x 100 11.19 H
  0.1000g
• O 0.03551 g O x 100 35.51 O
  0.1000g
• Total 100.00 (just checking . . .)

25
Combustion Analysisempirical formula

• Compound contains 0.004438 mol C, 0.01110 mol H,
  and 0.002219 mol O
• C.004438H.01110 O.002219
• C(.004438/.002219)H(.01110/.002219)O(.002219/.0022
  19)
• C2.000H5.000O1.000
• Empirical formula is C2H5O

26
Combustion Analysismolecular formula

• The empirical formula is C2H5O. The molar mass
  is approximately 90 g/mol
• True molar mass 90
  g/mol Empirical molar mass 2(12) 5(1)
  16
• True molar mass 90 g/mol
  2 Empirical molar mass 45 g/mol
• Molecular formula is C4H10O2

27
Combustion AnalysisExamples 3-6A and 3-6B

• Isobutyl propionate is composed of carbon,
  hydrogen, and oxygen. Combustion of 1.152 g of
  isobutyl propionate yields 2.726 g CO2 and 1.116
  g H2O. What is its empirical formula ?
• Thiophene is composed of carbon, hydrogen, and
  sulfur. Combustion of 1.505 g thiophene yields
  3.149 g CO2, 0.645 g H2O, and 1.146 g SO2, which
  accounts for all of the sulfur. What is the
  empirical formula of thiophene?

28
Oxidation states

• The oxidation state (O.S.) or oxidation number is
  a convenient but artificial way to describe the
  electron environment around an atom
• It is related to the number of electrons gained,
  lost, or apparently used in forming compounds
• Oxidation states are assigned using the rules on
  page 79 of your text (memorize these in order)

29
Assigning oxidation states

• 1. The O.S. of each atom in an element is zero.
• 2. The total of the O.S. of all atoms in any
  species (formula unit, molecule or ion) equals
  the charge on that species.
• 3. In compounds, Group 1A metals have O.S. 1
  and Group 2A metals have O.S. 2.
• 4. In compounds, the O.S. of fluorine is 1.
• 5. In compounds, the O.S. of hydrogen is 1.
• 6. In compounds, the O.S. of oxygen is 2.
• 7. In binary compounds with metals, the O.S. of
  a Group 7A element is 1, Group 6A element 2,
  and Group 5A element 3.

30
Assigning oxidation statesExamples 3-7A and 3-7B

• What is the oxidation state of the underlined
  element in
• S8 Cr2O72 Cl2O
  KO2
• 0 6 1
  1/2
• What is the oxidation state of the underlined
  element in
• S2O32 Hg2Cl2 KMnO4 H2CO
• 2 1 7
  0

31
Nomenclature Binary Ionic Compounds

• Binary ionic compounds metal nonmetal
• Nomenclature of binary ionic compounds
• Write name of metal cation (same as element name)
• Write name of nonmetal anion, with element name
  modified to end in ide
• No prefixes to indicate number of ions
• Roman numeral shows O.S. of transition metal
  cation
• Compound is electrically neutral, so in formula
  total cation charge total anion charge

32
Binary ionic compoundsExamples 3-8A and 3-8B

• Write the formulas for the compounds
• Lithium oxide
• Tin (II) fluoride
• Lithium nitride
• Write the formulas for the compounds
• Aluminum sulfide
• Magnesium nitride
• Vanadium (III) oxide

33
Binary ionic compoundsExamples 3-8A and 3-8B

• Write the formulas for the compounds
• Lithium oxide Li2O
• Tin (II) fluoride SnF2
• Lithium nitride Li3N
• Write the formulas for the compounds
• Aluminum sulfide Al2S3
• Magnesium nitride Mg3N2
• Vanadium (III) oxide V2O3

34
Binary ionic compoundsExamples 3-9A and 3-9B

• Write acceptable names for the compounds
• CsI CaF2 FeO CrCl3
• Write acceptable names for the compounds
• CaH2 CuCl Ag2S Hg2Cl2

35
Binary ionic compoundsExamples 3-9A and 3-9B

• Write acceptable names for the compounds
• CsI CaF2 FeO CrCl3
• cesium iodide iron (II) oxide
• calcium fluoride chromium (III) chloride
• Write acceptable names for the compounds
• CaH2 CuCl Ag2S Hg2Cl2
• calcium hydride silver (I) sulfide
• copper (I) chloride mecury (I) chloride

36
Nomenclature Binary Molecular Compounds

• Binary molecular compounds nonmetalnonmetal
• Nomenclature of binary molecular compounds
• Write name of element with positive O.S. first
• Write name of element with negative O.S. second,
  with element name modified to end in ide
• Use prefixes to indicate number of atoms of each
  element

37
Binary Molecular CompoundsExamples

• Write the formulas for the compounds
• Carbon tetrabromide
• Dinitrogen pentoxide
• Phosphorus triiodide
• Write acceptable names for the compounds
• SF6 Cl2O7 IBr3

38
Binary Molecular CompoundsExamples

• Write the formulas for the compounds
• Carbon tetrabromide CBr4
• Dinitrogen pentoxide N2O5
• Phosphorus triiodide PI3
• Write acceptable names for the compounds
• SF6 Cl2O7 IBr3
• sulfur hexafluoride
• dichlorine heptoxide
• iodine tribromide

Watch your spelling!
39
Nomenclature Binary acids

• Binary acids certain compounds of H nonmetal
• Produce hydrogen ions (H1) when dissolved in
  water
• Name as acid when focus is on behavior in water
• Write prefix hydro for hydrogen
• Write nonmetal element, with name modified to end
  in ic, then write acid
• Formula must be electrically neutral

40
Binary acidsExamples

• Write the formulas for the compounds
• Hydrochloric acid
• Hydroiodic acid
• Hydrosulfuric acid
• Write acceptable names for the compounds
• HBr H2S HF

41
Binary acidsExamples

• Write the formulas for the compounds
• Hydrochloric acid HCl
• Hydroiodic acid HI
• Hydrosulfuric acid H2S
• Write acceptable names for the compounds
• HBr H2S HF
• hydrobromic acid
• hydrosulfuric acid
• hydrofuoric acid

42
Nomenclature Polyatomic Ions

• Polyatomic ions are ions consisting of two or
  more covalently bound atoms that carry a charge
• Most are anions (exception ammonium, NH41)
• Very few polyatomic anion names end in ide
• Cyanide, CN1 Hydroxide, OH1
• Most names end in ate or ite

43
Nomenclature Oxoanions

• Polyatomic ions that contain oxygen are oxoanions
• A nonmetal may form several oxoanions with
  different numbers of oxygens
• As nonmetal O.S. increases (number of oxygens
  increases), name changes sysematically
• ClO1 ClO21 ClO31
  ClO41 hypochlorite chlorite
  chlorate perchlorate
• SO32 SO42 sulfite
  sulfate
• All common oxoanions of halogens are 1

44
Nomenclature Oxoanions

• Polyatomic ions that contain oxygen are oxoanions
• Some oxoanions include varying numbers of
  hydrogens
• PO43 HPO42 H2PO41 phosphate
  hydrogen phosphate dihydrogen phosphate
• O.S. of central nonmetal is constant ion charge
  changes as number of hydrogens varies
• Prefix thio indicates an S has substituted for
  an O
• SO42 S2O32 sulfate thiosulfate

45
Nomenclature Oxoacids

• Oxoacids are combinations of hydrogen ions (H1)
  and oxoanions
• H1 oxoanion acid, a molecular compound
• Metal ion oxoanion salt, an ionic compound
• Oxoacid name derived from oxoanion name
• Change ite to ous and ate to ic
• Add acid to end of name
• Formulas are electrically neutral

46
Nomenclature OxoacidsExamples

• Write acceptable names for the compounds
• H2SO3 HNO3 HClO
• Write the formulas for the compounds
• Phosphoric acid
• Nitrous acid
• Perchloric acid

47
Nomenclature OxoacidsExamples

• Write acceptable names for the compounds
• H2SO3 HNO3 HClO
• sulfurous acid nitric acid hypochlorous
  acid
• Write the formulas for the compounds
• Phosphoric acid H3PO4
• Nitrous acid HNO2
• Perchloric acid HClO4

48
NomenclatureExamples 3-10A and 3-10B

• Name the compounds
• SF6 HNO2 Ca(HCO3)2
  FeSO4
• NH4NO3 PCl3 HBrO AgClO4
  Fe2(SO4)3

49
NomenclatureExamples 3-10A and 3-10B

• Name the compounds
• SF6 HNO2 Ca(HCO3)2
  FeSO4
• Sulfur hexafluoride Calcium hydrogen carbonate
• Nitrous acid Iron (II) sulfate
• NH4NO3 PCl3 HBrO AgClO4
  Fe2(SO4)3
• Ammonium nitrate
• Phosphorus trichloride
• Hypobromous acid
• Ailver perchlorate
• Iron (III) sulfate

50
NomenclatureExamples3-11A and 3-11B

• Write formulas for the compounds
• Boron trifluoride
• Potassium dichromate
• Sulfuric acid
• Calcium chloride
• Aluminum nitrate
• Tetraphosphorous decoxide
• Chromium (III) hydroxide
• Iodic acid

51
NomenclatureExamples3-11A and 3-11B

• Write formulas for the compounds
• Boron trifluoride BF3
• Potassium dichromate K2Cr2O7
• Sulfuric acid H2SO4
• Calcium chloride CaCl2
• Aluminum nitrate Al(NO3)3
• Tetraphosphorous decoxide P4O10
• Chromium (III) hydroxide Cr(OH)3
• Iodic acid HIO3

52
Slaying the nomenclature dragon

• Make flash cards of all the ion names, formulas
  and charges and all the acid names and formulas
  (Tables 3.1, 3.3, and 3.4 in Chapter 3), and of
  the Greek prefixes (mono, di, tri, tetra, penta,
  hexa, hepta, octa, nona, deca)
• Concentrate on writing formulas from names
  (thats whats on the AP exam)
• For ionic formulas and acid, be sure charges
  balance!

53
Exercise 32

• The hemoglobin content of blood is about 15.5
  g/100 mL blood. The molar mass of hemoglobin is
  about 64,500 g/mol, and there are 4 Fe atoms in a
  hemoglobin molecule. Approximately how many Fe
  atoms are present in the 6 L of blood in a
  typical adult?

54
Exercise 38

• Determine the mass percent of each element in the
  antimalarial drug quinine, C20H24N2O2

55
Exercise 45

• Determin the empirical formula of
• Warfarin, 74.01 C, 5.23 H, and 20.76 O by
  mass
• Mustard gas, 30.20 C, 5.07 H, 44.58 Cl, and
  20.16 S by mass

56
Exercise 47

• Indigo has the mass composition 73.27 C, 3.84
  H, 10.68 N, and the remainder oxygen. Its
  molecular mass is 262.3 amu. What is the
  molecular formula of indigo?

57
Exercise 50

• The element X forms the chloride XCl4 containing
  75.0 Cl, by mass. What is the identity of
  element X?

58
Exercise 51

• A 0.2612 g sample of a hydrocarbon produces
  0.8661 g CO2 and 0.2216 g H2O in combustion
  analysis. Its molecular mass is found to be 106
  amu. Determine the mass composition, empirical
  formula, and molecular formula of this
  hydrocarbon.

59
Exercises 57 and 60

• Indicate the oxidations state of the underlined
  element
• CH4 SF4 Na2O2 C2H3O21
  FeO42
• Nitrogen forms five oxides. Write appropriate
  formulas for these compounds if the O.S. of N in
  them are 1, 2, 3, 4, and 5, respectively.

60
Exercise 62

• Name these compounds
• Ba(NO3)2 HNO2 CrO2 KIO3
  
• LiCN KIO Fe(OH)2
  Ca(H2PO4)2
• H3PO4 NaHSO4 Na2Cr2O7
  NH4C2H3O2
• MgC2O4 Na2C2O4

61
Exercise 64

• Assign suitable names to these compounds
• ICl ClF3 SF4 BrF5
  N2O4 S4N4

62
Exercise 66

• Write correct formulas for
• Magnesium perchlorate
• Lead (II) acetate
• Tin (IV) oxide
• Hydroiodic acid
• Chlorous acid
• Sodium hydrogen sulfite
• Calcium dihydrogen phosphate
• Aluminum phosphate
• Dinitrogen tetroxide
• Disulfur dichloride

63
Exercise 77

• A sample of MgSO4xH2O weighing 8.129 g is heated
  until all the water of hydration is driven off.
  The resulting anhydrous compound, MgSO4, weighs
  3.967 g. What is the formula of the hydrate?

64
Types of Compounds
Buckyball, C60
Methane, CH4
65
PREDICTING ION CHARGES

• metals lose electrons?? cations
• nonmetals gain electrons ? anions

66
MAIN GROUP METALS

• M ? n e- Mn
• where n group number on periodic table
• Group 1 Na ? 1 e- Na1
• Group 2 Mg ? 2 e- Mg2
• Group 3 Al ? 3 e- Al3

67
TRANSITION METALS

• Zn ? 2 e- Zn2
• Ag ? 1 e- Ag1
• Other transition metal ion charges not easily
  predicted from periodic table
• M2 or M3 are common

68
NONMETALS

• X n e- ? Xn- where n 8 group
  number
• Group 5 N (85) e- ? N3-
• Group 6 O (86) e- ? O2-
• Group 7 F (87) e- ? F1-

69
Symbols and Locations of Monatomic Ions
Sc3
Cd2
70
Molecular Compounds

• A molecule is a group of bonded atoms that exists
  as a distinct entity
• The atoms in a molecule are held together by
  covalent bonds
• Molecular compounds consist of discrete molecules

71
Water a molecular compound
72
Acetic acid a molecular compound
73
Molar Mass

• The mass of one mole of any element or compound
• H2O 2 H x 1.00794 2.01588 1 O x
  15.9994 15.9994 18.01528
• Molar mass of H2O 18.0153 g/mol

74
SOME MOLECULAR ELEMENTS
75
Molar mass and mole conceptExamples 3-1A and 3-1B

• What is the total number of ions present in a 1.0
  g sample of zinc oxide, ZnO?
• How many grams of MgCl2 are needed to provide 5.0
  x 1023 Cl1- ions?

76
Molar mass and mole conceptExamples 3-2A and 3-2B

• Gold has a density of 19.32 g/cm3. How many
  atoms of gold are in a piece of gold leaf that is
  2.50 cm on each side and 0.100 mm thick?
• If 1.0 mL of liquid ethyl mercaptan, C2H6S (d
  0.84 g/mL) is allowed to evaporate and distribute
  itself throughout a 1500 m3 room,will the vapor
  be detectable in the room? The limit of
  detectability is 9 x 10-4 mmol/m3.

77
Molar mass and mole conceptExamples 3-3A and 3-3B

• How many grams of C are contained in 75.0 mL of
  halothane, C2HBrClF3 (d 1.871 g/mL)?
• How many mL of halothane, C2HBrClF3 (d 1.871
  g/mL), contain 100.0 g Br?