What do you call a molecule that consists of a single atom?

A molecule that consists of a single atom is referred to as a monoatomic molecule. Monoatomic molecules typically consist of noble gases, such as helium, neon, argon, krypton, xenon, and radon, which exist as individual atoms due to their stable electron configurations. This stability prevents them from readily forming bonds with other atoms, resulting in the existence of these elements in their atomic state under normal conditions.

In contrast, polyatomic molecules contain two or more atoms bonded together, while diatomic molecules specifically consist of two atoms, which can be of the same element (like O2) or different elements (like CO). The term homogeneous molecule is not a defined term in this context and does not accurately describe any typical molecular structure. Hence, the identification of a monoatomic molecule captures the essence of the question regarding single-atom structures effectively.