Why do some compounds have the same empirical and molecular formulae?

Some compounds have the same empirical and molecular formulae because their molecular formula is the simplest whole number ratio of atoms.

In chemistry, the empirical formula of a compound represents the simplest whole number ratio of atoms of each element in the compound. It is the most reduced version of the compound's formula. On the other hand, the molecular formula represents the actual number of atoms of each element in a molecule of the compound.

For some compounds, the molecular formula is already in its simplest whole number ratio. This means that the empirical formula and the molecular formula are the same. For example, the molecular formula for water is H2O, which is also its empirical formula. This is because the ratio of hydrogen to oxygen atoms in a water molecule is 2:1, which is the simplest possible ratio.

However, for other compounds, the molecular formula is not in its simplest whole number ratio. For example, the molecular formula for glucose is C6H12O6, but its empirical formula is CH2O. This is because the ratio of carbon to hydrogen to oxygen atoms in a glucose molecule is 6:12:6, which simplifies to 1:2:1.

Therefore, whether a compound's empirical and molecular formulae are the same depends on whether the molecular formula is already in its simplest whole number ratio. This is determined by the specific arrangement and bonding of atoms in the compound. It's important to remember that while the empirical formula provides information about the ratio of atoms, it does not provide information about the compound's structure or the arrangement of its atoms.