Answer: The atom would become ionized and stable.
Explanation:
An atom can have utmost 8 electrons in its valence shell. A full valence shell means the atom has gained noble gas configuration which is the most stable configuration. An atom is said to be ionized when it gains or loses electrons. Here, with extra electrons, the atom would become a negative ion.
Thus, If an atom gains some extra electrons so that its valence shell becomes full, the atom would become ionized and stable.