1. Unit 6.5 Molar Mass Percent Composition Empirical Formulas
Molecular Formulas

2. Molar Mass
Add rounded atomic weights. Multiply them, if needed, by the subscript.
Ex) MgBr2

3. Percent Composition Found on Table T
% composition = mass of part x 100
mass of whole
Mass of whole = solute(solid/gas) +
solvent (liquid)

4. Chemical Formulas Structural Empirical Molecular
There are 3 types of chemical formulas:
Structural
Empirical
Molecular

5. 3 Types of Formulas
Molecular Formulas show the actual number of atoms needed to make the formula.
Empirical formulas are used to show the smallest number of atoms needed to make the molecule. The empirical formula denotes the smallest ratio possible.

6. Structural Formulas and Lewis Dot Diagrams for Covalent Bonds
Shows which atoms are bonded together
Lewis dot diagrams are used for this and are called structural formulas
Some structural formulas
are shown here:

7. Using Dot Diagrams to Write Structural Formulas
Using Lewis dot diagrams:
Step 1: Count the total number of valence electrons
for the entire molecule
Step 2: Place the electrons around the atoms so
that they all have 8. You may have to place more
than 1 pair between atoms.
Step 3: Then replace the pairs with dashes
between molecules as shown below:
Note: Not all structural formulas show the unshared
electron pairs

8. Simplifying Empirical Formulas
Some formulas will need to be simplified.
Ex: Step 1: S+6 and O-2
Step 2: S2O6 divide both subscripts by highest common denominator (2)
Step 3: SO3