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Understanding Chemical Formulas: Atoms to Moles at Microscopic & Macroscopic Levels

Learn how chemical formulas represent atom ratios in compounds, from microscopic to macroscopic perspectives. Explore ionic vs. covalent compounds, empirical formulas, and molecular formulas, with step-by-step guidance on determining molecular formulas from empirical data.

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Understanding Chemical Formulas: Atoms to Moles at Microscopic & Macroscopic Levels

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  1. Chemical Formulas Tell type & number atoms in compound Microscopic level: imagine 1 atom, molecule, or formula unit Formula gives atom ratios Macroscopic level: imagine working in lab Formula gives mole ratios

  2. Formulas Ex: 2H2O can mean 2 molecules of water 2 moles of water 2H2O molecules contain: 4 H atoms & 2 O atoms 2 Moles of H2O molecules contain: 4 moles of H atoms & 2 moles of O atoms

  3. What can say about CuSO45H2O? It’s hydrated salt 1 mole CuSO4 contains 5 moles water When heated water is driven off & anhydrous salt is left: CuSO4 mole ratio in formula can be used to predict how much water found in any size sample If had 2 moles of CuSO45H2O, how much water would you lose on heating?

  4. Ionic vs. Covalent Formulas • By looking at the type of atoms, we can decide if the substance is an ionic compound or a molecular (covalent) compound. Molecular (covalent) compounds have all nonmetals. Ionic compounds usually have metal + nonmetal.

  5. Empirical Formulas

  6. Empirical Formula Smallest whole # ratio of elements in compound Ionic compounds have only empirical formulas Covalent compounds have empirical and molecular formulas

  7. Molecular Formulas

  8. Molecular Formulas Gives exact composition of molecule Molecular compounds have both empirical and molecular formulas can be same or different

  9. Relationship between empirical and molecular formulas molecular formula is whole number multiple of empirical formula Molecular Formula = n (Empirical Formula) n is small whole number multiplies subscripts sometimes, n = 1

  10. Molecular Formula If know empirical formula and molar mass, can find molecular formula Step 1: Find mass of empirical formula Step 2:__Molar mass__ = whole number (n) Empirical mass Step 3: Multiply subscripts in empirical formula by n

  11. Finding Molecular Formulas Find molecular formula for substance whose empirical formula is CH and whose molar mass = 78.0 g Step 1: Empirical mass = 13.0 g Step 2: Molar mass = n Empirical mass 78g = 6 13g Step 3: 6 x subscripts in CH = C6H6

  12. Say everything you can about: NaCl C6H6 C6H12O6 CH4 CF4 BeSO4 C8H18 KI C2H4Cl2 CaBr2 CuSO45H2O Covalent, molecular Ionic, empirical Covalent, molecular Covalent, empir., molec? Covalent, empirical, molecular? Ionic, empirical Ionic, empirical Covalent, molecular Covalent, molecular Ionic, empirical Ionic, empirical

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