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

Formulas Ex: 2H2O can mean 2H2O molecules contain: 4 H atoms & 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

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52O, how much water would you lose on heating?

Empirical Formulas

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

Molecular Formulas

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

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

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

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