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Published byAlice Allison Modified over 9 years ago
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Topic: Chemical Formulas Do Now: from last years regents
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Chemical Formulas Tell type & number atoms in compound Microscopic level: Formula gives atom ratios Microscopic level: Formula gives atom ratios Macroscopic level: Formula gives mole ratios Macroscopic level: Formula gives mole ratios
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EXAMPLE 2H 2 O can mean 2H 2 O can mean 2 molecules of water 4 H atoms & 2 O atoms 4 H atoms & 2 O atoms 2 moles of water 4 moles of H atoms & 2 moles of O atoms 4 moles of H atoms & 2 moles of O atoms NOTE: WATER IS A BINARY COMPOUND – contains 2 elements only
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What happens when a chemical formula contains CuSO 4 5H 2 O Means contains In this case it contains water so it’s called a hydrate
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Types of formulas
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Empirical Formula Smallest whole # ratio of elements in compound CH 4 C 2 H 6 C 5 H 10
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Molecular Formulas Gives exact composition of molecule CH 4 C 2 H 6 C 5 H 10
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Relationship between empirical and molecular formulas molecular formula is whole number multiple of empirical formula Molecular Formula = n (Empirical Formula) n (Empirical Formula) C 4 H 8 = 4(CH 2 ) C 4 H 8 = 4(CH 2 )
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Ionic Compounds Metal and Nonmetal Their formulas are always empirical NaCl Fe 2 O 3
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Covalent Molecules Nonmetal only Formulas can be empirical or molecular – need to know mass to determine CH 4 C 2 H 6 C 5 H 10
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Say everything you can about: NaClC 6 H 6 C 6 H 12 O 6 CH 4 CF 4 BeSO 4 C 8 H 18 KIC 2 H 4 Cl 2 CaBr 2 CuSO 4 5H 2 O empirical Covalent, empir., molec? Covalent, molecular Ionic, empirical Covalent, molecular Covalent, empirical, molecular? Ionic, empirical Covalent, molecular Ionic, empirical Covalent, molecular
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Lets practice- page 20
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Molecular Formula If know empirical formula and molar mass, can find molecular formula Example: Find molecular formula for substance whose empirical formula is CH 2 and whose molar mass = 84.0 g Step 1: Find mass of empirical formula Step 2:Molar mass = whole # (n) Empirical mass Step 3: Multiply subscripts in empirical formula by n Step 1: C = 1 x 12 = 12 H = 2 x 1 = _2 14 g Step 2: 78g = 6 14g Step 3: 6 CH 2 = C 6 H 12
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