The key difference between molecular and empirical formulas lies in the level of detail they provide about the composition of a chemical compound: the empirical formula shows the simplest whole-number ratio of atoms, while the molecular formula shows the actual number of each type of atom present in a molecule.
Detailed Explanation
Here's a breakdown of the differences:
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Empirical Formula: This formula represents the simplest whole number ratio of elements in a compound. It's derived by reducing the subscripts in the molecular formula to their lowest common denominator. It tells you the relative proportions of each element, but not necessarily the actual number of atoms in a single molecule.
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Molecular Formula: This formula indicates the exact number of each type of atom present in a single molecule of a compound. It's a whole number multiple of the empirical formula.
Examples to Illustrate the Difference
Let's consider a few examples:
| Compound | Molecular Formula | Empirical Formula | Explanation |
|---|---|---|---|
| Water | H2O | H2O | The simplest ratio of H to O is 2:1. The molecule is H2O. |
| Glucose | C6H12O6 | CH2O | The ratio of C:H:O is 6:12:6, which simplifies to 1:2:1. |
| Hydrogen Peroxide | H2O2 | HO | The ratio of H:O is 2:2, which simplifies to 1:1. |
| Benzene | C6H6 | CH | The ratio of C:H is 6:6, which simplifies to 1:1. |
| Diethyl Ether | C4H10O | C2H5O | The ratio of C:H:O is 4:10:1, which simplifies to 2:5:0.5. Since empirical formulas require whole numbers, one should double it to make the smallest integers. You also cannot have a decimal in the ratio, making the result C4H10O |
Key Takeaways
- The empirical formula is derived from the molecular formula.
- The molecular formula is a whole-number multiple of the empirical formula. This multiple can be 1 (as with water).
- Different compounds can have the same empirical formula but different molecular formulas (e.g., acetylene and benzene both have the empirical formula CH). This means knowing only the empirical formula isn't enough to identify the compound uniquely.
- The molecular formula provides more specific information about the actual composition of a molecule.
In summary, the empirical formula provides the simplest ratio of elements in a compound, while the molecular formula provides the actual number of atoms of each element in a single molecule of that compound.
