Kaplan Nursing Entrance Practice Exam

How is a molecule defined?

1. Single atom

2. Collection of cells

3. Two or more atoms combined

4. Any large compound

The correct answer is: Two or more atoms combined

A molecule is defined as two or more atoms that are chemically bonded together. This definition encompasses a wide variety of substances, including elements (like O2, which consists of two oxygen atoms) and compounds (like H2O, which is made up of two hydrogen atoms and one oxygen atom). The focus is on the interaction between atoms that results in a stable configuration due to chemical bonds, distinguishing a molecule from simply a single atom or a collection of cells. In the context of the other choices, a single atom refers to elements in their purest form, which do not form molecules by themselves unless they bond with other atoms. A collection of cells relates to biological structures rather than molecular chemistry, as cells are a higher level of organization in living organisms. Lastly, describing a molecule as any large compound is misleading, since not all compounds are large; some molecules consist of just two atoms. Therefore, identifying a molecule as two or more atoms combined gives a precise understanding of its fundamental nature in chemistry.