Answer:
An atom that has an outer shell that is not full is more likely to be reactive than an atom that has a full outer shell.
Step-by-step explanation:
Atoms with filled outer shells are quite stable compared to atoms with partially filled outer shells.
Atoms with filled shells are are not reactive ordinarily unless they are stimulated. They have no unpaired electrons they could make them reactive.
Atoms with unfilled outer shells react by forming ionic or covalent bond with other electrons.
They form ionic bonds by donating the outermost (valence) electrons to another atom or receiving electrons from another atom to fill up their outermost shells.
They form covalent bonds with other similar atoms through sharing of outermost electrons.