Question

What can we tell about a compound when we know the empirical formula? What additional information is conveyed by the molecular formula? By the structural formula? Explain in each case.

Short answer

In summary, an empirical formula indicates the simplest whole number ratio of elements in a compound, but it does not reveal the molecular structure or exact number of atoms in a molecule. Molecular formulas provide the precise number of atoms of each element in a molecule, but they do not show the structural arrangement. Finally, structural formulas display the arrangement of atoms, bonds, and functional groups, which yields comprehensive information about the compound's structure, shape, stereochemistry, and reactivity. For example, glucose has an empirical formula of CH_2O, a molecular formula of C_6H_12O_6, and a specific structural formula that includes a six-carbon cyclic molecule with strategically placed hydroxyl groups (-OH).

Step-by-step solution

Empirical Formula

The empirical formula of a compound represents the simplest whole number ratio of the elements that make up the compound. From the empirical formula, we can tell the simplest proportion of the elements in the compound. However, the empirical formula does not reveal the exact number of atoms of each element present in the molecule or the actual structure of the molecule. For example, the empirical formula for glucose is CH_2O. This tells us that there is a 1:2:1 ratio of carbon, hydrogen, and oxygen atoms. However, we cannot deduce the molecular structure or the exact number of atoms in one molecule from this information.

Molecular Formula

The molecular formula of a compound provides additional information beyond the empirical formula. A molecular formula states the exact number of atoms of each element found in a single molecule of the compound. Using the previous example, the molecular formula of glucose is C_6H_12O_6. This tells us that each glucose molecule contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. The molecular formula can also be found as a multiple of the empirical formula. However, the molecular formula still does not reveal the structural layout or arrangement of atoms in the molecule.

Structural Formula

The structural formula of a compound provides the most information about a compound. It depicts the arrangements of atoms in the molecule, including the type and location of bonds between the atoms and any functional groups present. It is a graphical representation of the compound's molecular structure. Returning to the example of glucose, the structural formula shows that glucose is a six-carbon cyclic molecule with specific configurations of hydroxyl groups (-OH) strategically placed within the structure. The structural formula reveals information about the compound's overall shape, stereochemistry, and reactivity. In conclusion, the empirical formula provides information about the simplest whole number ratio of elements in a compound, while the molecular formula conveys the exact number of atoms of each element in the molecule. The structural formula displays the arrangement of atoms and bonds in the molecule, providing the most comprehensive information about the compound.