The molecular formula, empirical formula, and structural formula each represent a chemical compound, but they provide different levels of detail about its composition and structure. Here's how they differ:
Molecular Formula
- Definition: A molecular formula shows the exact number of each type of atom in a molecule.
- Information Provided: Identifies the constituent elements and their actual quantities in a single molecule of the compound.
- Example: Glucose has the molecular formula C6H12O6, indicating that each glucose molecule contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.
Empirical Formula
- Definition: The empirical formula represents the simplest whole-number ratio of atoms in a compound.
- Information Provided: Shows the relative proportions of each element, but not necessarily the actual number of atoms in a molecule.
- Derivation: Obtained by simplifying the subscripts in the molecular formula to the lowest possible whole numbers.
- Example: For glucose (C6H12O6), the empirical formula is CH2O (dividing each subscript by 6). This means that the ratio of carbon to hydrogen to oxygen is 1:2:1.
- Note: Different compounds can have the same empirical formula. For example, acetic acid (C2H4O2) also has an empirical formula of CH2O.
Structural Formula
- Definition: A structural formula shows the arrangement of atoms and the bonds between them within a molecule.
- Information Provided: Depicts how atoms are connected, including single, double, and triple bonds. This provides information about the molecule's shape and connectivity.
- Representation: Can be represented in various forms, including Lewis structures, condensed structural formulas, and skeletal formulas.
- Example: The structural formula of ethanol (C2H6O) would show how the two carbon atoms are connected, with one carbon bonded to three hydrogen atoms, the other carbon bonded to two hydrogen atoms and an oxygen atom, and the oxygen atom bonded to a hydrogen atom. This visual representation helps understand the molecule's geometry and reactivity.
Summary Table
| Feature | Molecular Formula | Empirical Formula | Structural Formula |
|---|---|---|---|
| Definition | Exact number of atoms in a molecule | Simplest whole-number ratio of atoms in a compound | Arrangement of atoms and bonds within a molecule |
| Information | Actual number of each element | Relative proportions of elements | Connectivity and bonding within the molecule |
| Example | C6H12O6 (Glucose) | CH2O (Glucose) | Shows the arrangement of atoms in ethanol (C2H6O) |
| Uniqueness | Unique for each molecule | Different molecules can have the same empirical formula | Provides distinct structural information |
In essence, the molecular formula gives the complete count, the empirical formula provides the simplest ratio, and the structural formula reveals the architecture of the molecule.
