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Molecules, Compounds, and Chemical Equations

Molecules, Compounds, and Chemical Equations. Chapter 3. 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

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Molecules, Compounds, and Chemical Equations

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  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 Chloride:an 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 CH3–C–OH 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) N1.000O1.998 • 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 compound’s 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. Determining a Formula using Combustion Analysis

  18. 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

  19. 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

  20. 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 C+H = 0.03551 g O x 1 mol = 0.002219 mol O 15.9994 g

  21. 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 . . .)

  22. Combustion Analysis:empirical 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/.002219) • C2.000H5.000O1.000 • Empirical formula is C2H5O

  23. Combustion Analysis:molecular 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 = 2Empirical molar mass 45 g/mol • Molecular formula is C4H10O2

  24. 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)

  25. 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.

  26. Assigning oxidation statesExamples 3-7A and 3-7B • What is the oxidation state of the underlined element in • S8Cr2O72–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

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

  32. Nomenclature: Binary Molecular Compounds • Binary molecular compounds: nonmetal+nonmetal • 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

  33. Binary Molecular CompoundsExamples • Write the formulas for the compounds • Carbon tetrabromide • Dinitrogen pentoxide • Phosphorus triiodide • Write acceptable names for the compounds • SF6 Cl2O7 IBr3

  34. 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!

  35. 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

  36. Binary acidsExamples • Write the formulas for the compounds • Hydrochloric acid • Hydroiodic acid • Hydrosulfuric acid • Write acceptable names for the compounds • HBr H2S HF

  37. 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

  38. 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”

  39. 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 chlorateperchlorate SO32– SO42–sulfite sulfate • All common oxoanions of halogens are –1

  40. 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

  41. 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

  42. Nomenclature: OxoacidsExamples • Write acceptable names for the compounds • H2SO3 HNO3 HClO • Write the formulas for the compounds • Phosphoric acid • Nitrous acid • Perchloric acid

  43. 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

  44. NomenclatureExamples 3-10A and 3-10B • Name the compounds • SF6 HNO2 Ca(HCO3)2 FeSO4 • NH4NO3 PCl3 HBrO AgClO4 Fe2(SO4)3

  45. 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

  46. 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

  47. 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

  48. 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 (that’s what’s on the AP exam) • For ionic formulas and acid, be sure charges balance!

  49. 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?

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