What is a molecule?

A molecule is defined as the smallest unit of a compound that retains all the chemical properties of that compound. When atoms bond together, they form molecules, which can consist of two or more atoms. This unique arrangement allows the molecule to exhibit the specific characteristics of the compound it represents, such as its reactivity, phase, and behavior in chemical reactions.

For example, a water molecule (H2O) consists of two hydrogen atoms and one oxygen atom bonded together. This specific combination results in the properties of water we recognize, such as its liquid state at room temperature and its ability to dissolve many substances. Understanding this definition is crucial for recognizing how compounds behave and interact in various chemical processes.

In contrast, a molecule does not simply refer to a single element, which would be the focus of the first choice, nor does it represent electron clouds or collections of particles outside an atom, as noted in the other options. Each of those alternatives fails to capture the essence of what constitutes a molecule in terms of its relationship as the fundamental unit of a compound.