Yes, the chemical formula \(\text{NH}_3\) is an empirical formula, and it is also its molecular formula. This situation arises because the ratio of nitrogen to hydrogen atoms in ammonia cannot be simplified further, meaning the compound’s actual composition and its simplest ratio are exactly the same. Understanding why this is the case requires looking at the fundamental definitions of the two main types of chemical formulas used in chemistry: the empirical formula and the molecular formula.
Defining the Empirical Formula
The empirical formula represents the smallest whole-number ratio of atoms of each element in a compound. It is often called the simplest formula because the subscripts for each element have been reduced as far as possible by dividing by their greatest common factor. This formula is determined experimentally, usually from the percent composition by mass of the elements found in a sample of the substance. For a compound like water (\(\text{H}_2\text{O}\)), the ratio of hydrogen to oxygen is 2:1, which is already the simplest whole-number ratio, so its empirical formula is also \(\text{H}_2\text{O}\). The empirical formula provides limited information about the actual structure, but it is fundamental to understanding the compound’s elemental proportions.
The Role of the Molecular Formula
In contrast to the empirical formula, the molecular formula shows the exact number of atoms of each element present in a single molecule of a compound. It provides a complete picture of the molecule’s composition, indicating the actual count of atoms rather than just the ratio. The relationship between the two formulas is straightforward: the molecular formula is always an integer multiple of the empirical formula. In many cases, the molecular formula is identical to the empirical formula. However, for other compounds, the formulas differ significantly. For instance, the sugar glucose has a molecular formula of \(\text{C}_6\text{H}_{12}\text{O}_6\). When the subscripts in the glucose formula are divided by the greatest common factor of six, the result is the empirical formula \(\text{CH}_2\text{O}\).
Analyzing Ammonia (\(\text{NH}_3\))
The ammonia molecule is composed of one nitrogen atom covalently bonded to three hydrogen atoms, making its molecular formula \(\text{NH}_3\). To determine the empirical formula, one must check if these subscripts can be reduced by dividing them by a common whole number greater than one. The ratio of nitrogen to hydrogen atoms is 1:3, and there is no common factor that can divide both 1 and 3 to yield smaller whole numbers. Since the formula \(\text{NH}_3\) cannot be mathematically simplified, it satisfies the definition of the empirical formula. Therefore, ammonia is a compound where the empirical formula and the molecular formula are identical.