Which statement correctly distinguishes molecular formula from empirical formula?

Which statement correctly distinguishes molecular formula from empirical formula?

• A. Empirical formula shows the smallest whole-number ratio of atoms.
• B. Molecular formula gives the actual number of atoms in a molecule.
• C. The molecular formula is always a multiple of the empirical formula.
• D. The empirical formula is identical to the molecular formula for all compounds.

Answer: (B)

The key idea is the distinction between the actual counts of atoms in a molecule and the simplest whole-number ratio of those atoms. The molecular formula shows exactly how many atoms of each element are present in one molecule. For example, glucose has a molecular formula C6H12O6, revealing six carbons, twelve hydrogens, and six oxygens per molecule. The empirical formula, CH2O, gives only the smallest ratio of elements (1 C : 2 H : 1 O) and does not convey the real numbers in a molecule. This difference is why the statement stating that the molecular formula provides the actual numbers of atoms is the best choice. It captures the essential function of the molecular formula, whereas the empirical formula is about the simplest ratio, not the exact counts. Some compounds do have identical empirical and molecular formulas (when the numbers are already in the smallest whole-number ratio), while for others the molecular formula is a multiple of the empirical one (as with glucose, where C6H12O6 is 6 times CH2O). The empirical formula being identical to the molecular formula for all compounds is not correct.

The key idea is the distinction between the actual counts of atoms in a molecule and the simplest whole-number ratio of those atoms. The molecular formula shows exactly how many atoms of each element are present in one molecule. For example, glucose has a molecular formula C6H12O6, revealing six carbons, twelve hydrogens, and six oxygens per molecule. The empirical formula, CH2O, gives only the smallest ratio of elements (1 C : 2 H : 1 O) and does not convey the real numbers in a molecule.

This difference is why the statement stating that the molecular formula provides the actual numbers of atoms is the best choice. It captures the essential function of the molecular formula, whereas the empirical formula is about the simplest ratio, not the exact counts. Some compounds do have identical empirical and molecular formulas (when the numbers are already in the smallest whole-number ratio), while for others the molecular formula is a multiple of the empirical one (as with glucose, where C6H12O6 is 6 times CH2O). The empirical formula being identical to the molecular formula for all compounds is not correct.