Final answer:
An atom with a full valence shell is referred to as an inert or noble gas, which is stable and chemically unreactive. In contrast, atoms with incomplete valence shells are reactive and form bonds to achieve stability.
Step-by-step explanation:
An atom that is unlikely to react or create bonds due to having a full valence shell is known as an inert gas or a noble gas. These gases have complete outer shells, typically with eight electrons (or two in the case of helium), providing them with a stable electron configuration that is chemically unreactive. Atoms seek stability in their electron configurations, and a full valence shell represents the most stable state, according to the octet rule. This contrasts with atoms that have incomplete valence shells, which are generally highly reactive and form bonds to achieve stability.
For instance, atoms with just one or two valence electrons, such as alkali and alkaline earth metals, will readily lose these electrons to form positive ions or cations. In contrast, nonmetals with one or two electrons less than a full shell will tend to gain electrons, forming negative ions, or share electrons to create covalent bonds.