Defining the Molecular Formula
A molecular formula is a chemical formula that specifies the exact number of atoms of each element present in a single molecule of a compound. Unlike an empirical formula, which shows the simplest whole-number ratio of atoms, the molecular formula reflects the actual composition of the molecule, providing a complete picture of its atomic makeup.
Components and Representation
The molecular formula is composed of the chemical symbols for each element, followed by a subscript number indicating the quantity of atoms of that element in the molecule. If only one atom of an element is present, no subscript is used. For instance, the molecular formula for water is H₂O, signifying two hydrogen atoms and one oxygen atom in each molecule.
Practical Examples
Consider glucose, a common sugar. Its molecular formula is C₆H₁₂O₆, meaning each glucose molecule contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. In contrast, its empirical formula is CH₂O, representing the simplest ratio. Another example is ethanol, with a molecular formula of C₂H₆O, clearly showing two carbons, six hydrogens, and one oxygen per molecule.
Importance in Chemistry
Knowing a compound's molecular formula is crucial for several reasons. It allows chemists to calculate the accurate molar mass of the compound, which is essential for stoichiometry and quantitative analysis. Furthermore, it helps in distinguishing between different compounds that might have the same empirical formula but distinct molecular structures and properties, such as isomers.