1. More About Formulas

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

3. Formulas Ex: 2H2O can mean
2 molecules of water
2 moles of water.
2H2O molecules have 4 hydrogen atoms & 2 oxygen atoms.
2 Moles of H2O molecules have 4 moles of hydrogen atoms & 2 moles of oxygen atoms.

4. What can you say about CuSO45H2O?
It’s a hydrated salt.
For every mole of CuSO4, there are 5 moles of water.
If it’s heated, it dries out. The water goes into the air and you’re left with the anhydrous salt, CuSO4.
The mole ratio in the formula can be used to predict how much water would be given off by any size sample.
If you had 2 moles of CuSO45H2O, how much water would you lose on heating?

5. Percent Water in CuSO4•5H2O
Step 1: Calculate the formula mass.
Mass of salt + Mass of water
Percent = (Part/Whole) X 100%
% H2O = Mass H2O/Formula Mass X 100 %

6. 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 compounds have all nonmetals.
Ionic compounds usually have metal + nonmetal.

7. Empirical Formula
Smallest whole number ratio of the elements in the compound.
Ionic compounds have only empirical formulas.
Covalent compounds have empirical and molecular formulas. They can be the same or different.

8. Molecular Formulas For covalent (molecular) compounds.
Give the exact composition of the molecule.
Molecular compounds have both empirical and molecular formulas. They can be the same or different.

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

10. Say everything you can about
PH3 C2H4 Al2O3
SrI2 NF3 H2Se
CH3OH SiO2 H2O2
CCl4 XeF4 P4O10

11. Relationship between empirical and molecular formulas
The molecular formula is a whole number multiple of the empirical formula.
Molec. Formula = n (Empirical Form.)
n is a small whole number, which multiplies the subscripts. Sometimes, n = 1.

12. Molecular Formula
If you know the empirical formula and the molar mass, you can find the molecular formula.
Step 1: Find the mass of the empirical formula.
Step 2: Molar mass  Empirical mass = small whole number, n
Step 3: Multiply the subscripts in the empirical formula by n.

13. Finding Molecular Formulas
Find the molecular formula for the 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 = 78.0/13.0
n = 6.
Step 3: 6 X subscripts in CH = C6H6.
Empirical mass