Molecular Formulas

• A molecular formula represents the actual numbers of atoms of different elements elements in one molecule of a compound.

Ex.

• An example is NO2. Experimental data indicates that the molecular mass of this compound is  about 92.02g/mol.  What is the molecular formula of this compound?
• First, calculate the sum of the atomic masses for NO2 . Look up the atomic masses for the elements from the Periodic table . The atomic masses are found here:
• Nitrogen is 14.0
• Oxygen  is 16.0

• Plugging in these numbers, the sum of the atomic masses for NO2 is:
•                     (14.0) + 2(16.0) = 46

• This means the formula mass of NO2 is 46.0. Compare the formula mass (46.0) to the approximate molecular mass (92.02). The molecular mass is twice the formula mass (92.02/46 = 2.0), so the simplest formula must be multiplied by 2 to get the molecular formula:
• The answer: 2 x NO2 = N204

- George Spencer