Two ways that an atom can achieve a stable electron configuration
1) By gaining or losing electrons: An atom can achieve a stable electron configuration by either gaining or losing electrons to fill its outermost energy level. For example, if an atom has 7 electrons in its outermost energy level (valence shell) and it gains one electron, it will have a stable configuration of 8 electrons. This process is known as electron gain or loss, and it occurs through chemical reactions such as ionization or bonding.
2) By sharing electrons: Another way an atom can achieve a stable electron configuration is by sharing electrons with other atoms through covalent bonding. In a covalent bond, atoms share electron pairs to achieve a full outer shell. This allows each atom to have a stable configuration by filling their valence shells with shared electrons. For example, in a water molecule, the oxygen atom shares two electrons with two hydrogen atoms to achieve a stable configuration of 8 electrons.