The structural formulas of the compounds \(n\) -butane and isobutane are shown below. (a) Determine the molecular formula of each. (b) Determine the empirical formula of each. (c) Which formulas-empirical, molecular, or structural-allow you determine these are different compounds?

Molecular formulas show the actual number of atoms of each element in a molecule. Empirical formulas show the simplest whole number ratio of atoms of each element in a compound. Structural formulas, on the other hand, indicate how the atoms are arranged and bonded to each other in a molecule. Therefore, structural formulas provide more information about the molecule than molecular and empirical formulas.

Here are the structural formulas for n-butane and isobutane: n-butane: H H H H | | | | C-C-C-C | | | | H H H H isobutane: H H H | | | H-C-C-C-H | | H H We can count the atoms of each element to determine their molecular and empirical formulas.

From the structural formulas, we can easily count the number of carbon and hydrogen atoms in each compound: For n-butane: 4 carbon (C) atoms and 10 hydrogen (H) atoms Therefore, its molecular formula is: \(C_4H_{10}\) For isobutane: 4 carbon (C) atoms and 10 hydrogen (H) atoms Therefore, its molecular formula is: \(C_4H_{10}\) Both compounds have the same molecular formula.

Since both compounds have the same molecular formula, their empirical formulas will also be the same. Their empirical formula will be the simplest whole number ratio of carbon and hydrogen atoms: Dividing both numbers of atoms by their greatest common divisor, which is 2, we obtain 2 and 5. Therefore, the empirical formula of both n-butane and isobutane is: \(C_2H_5\)

Now that we have determined the molecular and empirical formulas for n-butane and isobutane, we can see that these formulas are the same for both compounds, so neither molecular nor empirical formulas can be used to differentiate between them. However, the structural formulas of both compounds are different, indicating that they have different arrangements and bonding patterns of atoms. Thus, the structural formula is the one that allows us to determine that n-butane and isobutane are different compounds. In summary: (a) Molecular formula for n-butane and isobutane: \(C_4H_{10}\) (b) Empirical formula for n-butane and isobutane: \(C_2H_5\) (c) The structural formula allows us to determine that n-butane and isobutane are different compounds.