1. Chemical Formulas
Section 3.4

2. Empirical Formula
The empirical formula of a compound is the formula that gives that simplest whole number ratio in which the atoms of the elements in the compound are present.
The empirical formula of glucose, C6H12O6 (ratio of atoms is 6:12:6) is CH2O, as this is the lowest ratio (1:2:1) of the atoms C, H and O.

6. Molecular Formula
The molecular formula of a compound is the formula that gives the actual number of atoms of each element present in a molecule of the compound.

8. Percentage Composition by Mass
If the empirical formula of a compound is known, the percentage by mass of each element present can be calculated. It can be useful to calculate the percentage of a certain element in a compound, for example the percentage of nitrogen in fertilisers.

10. Structural Formulas
The structural formula of a compound shows the arrangement of the atoms within a molecule of the compound.
Some Examples:
You will come across many more structural formulas in the organic section of the course.
Methane, CH4
Ethene, C2H4
Ethanol, C2H5OH