Ch.2 - Atoms, Molecules, and Ions

Problem 45b

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Chapter 2, Problem 45b

The structural formulas of the compounds n-butane and isobutane are shown below. (b) Determine the empirical formula of each.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Empirical Formula

The empirical formula of a compound represents the simplest whole-number ratio of the elements present in that compound. It is derived from the molecular formula by dividing the subscripts of each element by their greatest common divisor. For example, the empirical formula for C6H12 is CH2, indicating that for every carbon atom, there are two hydrogen atoms.

Structural Formulas

Structural formulas depict the arrangement of atoms within a molecule, showing how the atoms are bonded to each other. They provide insight into the molecular geometry and can help identify isomers, which are compounds with the same molecular formula but different structural arrangements. Understanding structural formulas is crucial for determining the empirical formula accurately.

Isomers

Isomers are compounds that share the same molecular formula but differ in the arrangement of atoms, leading to different properties. For instance, n-butane and isobutane are structural isomers, meaning they have the same molecular formula (C4H10) but different structural formulas. Recognizing isomers is essential when calculating empirical formulas, as it affects the interpretation of the molecular structure.

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Isomers

Related Practice

Massspectrometry is more often applied to molecules than to atoms. We will see in Chapter 3 that the molecular weight of a molecule is the sum of the atomic weights of the atoms in the molecule. The mass spectrum of H₂ is taken under conditions that prevent decomposition into H atoms. The two naturally occurring isotopes of hydrogen are ¹H (atomic mass = 1.00783 amu; abundance 99.9885%) and ²H (atomic mass = 2.01410; abundance 0.0115%). (c) Which peak will be the largest, and which the smallest?

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Textbook Question

For each of the following elements, write its chemical symbol, locate it in the periodic table, give its atomic number, and indicate whether it is a metal, metalloid, or nonmetal: (g) arsenic.

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Textbook Question

For each of the following elements, write its chemical symbol, determine the name of the group to which it belongs (Table 2.3), and indicate whether it is a metal, metalloid, or nonmetal: (e) sulfur.

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Textbook Question

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

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Textbook Question

Ball-and-stick representations of benzene, a colorless liquid often used in organic chemistry reactions, and acetylene, a gas used as a fuel for high-temperature welding, are shown below. (a) Determine the molecular formula of each.

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Textbook Question

What are the molecular and empirical formulas for each of the following compounds? Write the molecular formula for the following compound.

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