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 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

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

4. Empirical Formulas

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

6. Molecular Formulas

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

8. 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

9. 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

10. 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