http://www.ck12.org Chapter 7. Chemical Nomenclature
7.2 Molecular Compounds
Lesson Objectives
- Describe the difference between an ionic compound and a molecular compound.
- Name a molecular compound given its formula.
- Write the correct formula for a molecular compound given its name.
Lesson Vocabulary
- binary molecular compound
Check Your Understanding
Recalling Prior Knowledge
- Describe the relationships between the following: atom, element, molecule, and compound.
Inorganic chemical compounds can be broadly classified into two groups: ionic compounds and molecular com-
pounds. In the last lesson, we learned that the structure of all ionic compounds is an extended three-dimensional
array of alternating positive and negative ions. Since ionic compounds do not take the form of individual molecules,
they are represented by empirical formulas. Now we will begin to examine the formulas and nomenclature of
molecular compounds.
Molecular Compounds
Molecular compounds are chemical compounds that take the form of discrete molecules. Examples include such
familiar substances as water (H 2 O) and carbon dioxide (CO 2 ) (Figure7.5). These compounds are very different
from ionic compounds like sodium chloride (NaCl). Ionic compounds are formed when metal atoms lose one or
more of their electrons to nonmetal atoms. The resulting cations and anions are electrostatically attracted to each
other. You will learn more about ionic chemical bonding in the chapter,Ionic and Metallic Bonding.
So what holds the atoms of a molecule together? Rather than forming ions, the atoms of a molecule share their
valence electrons in such a way that a bond forms between pairs of atoms. In a carbon dioxide molecule, there are
two of these bonds, each occurring between the carbon atom and one of the two oxygen atoms.
Larger molecules can have many, many bonds that serve to keep the molecule together. In a large sample of a given
molecular compound, all of the individual molecules are identical.