Electrons have a tendency to achieve a full outer shell, often referred to as the octet rule, which states that atoms are most stable when their outermost energy level is fully occupied with eight electrons. This stability is associated with a lower energy state, and it is based on several factors:
Electrostatic forces: Electrons are negatively charged particles, and according to Coulomb's law, like charges repel each other. By achieving a full outer shell, atoms minimize electron-electron repulsion, resulting in a more stable arrangement.
Energy considerations: When an atom has a full outer shell, its electrons are in their lowest energy states, which corresponds to a more stable configuration. By filling the outer shell, an atom reduces its overall energy.
Ionization energy: Elements with incomplete outer shells have a lower ionization energy, which is the energy required to remove an electron from an atom. By acquiring additional electrons and completing the outer shell, atoms increase their ionization energy and become more difficult to ionize. This stability is due to the fact that removing an electron from a full shell would require a significant amount of energy.
Electron affinity: Atoms with incomplete outer shells have a higher electron affinity, which is the energy change that occurs when an atom gains an electron. By gaining electrons and completing the outer shell, atoms release energy and become more stable.
Noble gas configuration: The noble gases (group 18 elements) have full outer shells and are known for their exceptional stability and low reactivity. Other elements seek to achieve a similar stable configuration as the noble gases by acquiring or losing electrons.
It is important to note that the octet rule is a useful guideline for understanding the general behavior of atoms in forming chemical bonds. However, there are exceptions to the octet rule, particularly for elements with fewer than eight electrons in their valence shell, such as hydrogen (H), helium (He), and elements in the d- and f-blocks of the periodic table. These elements have different rules and may exhibit expanded or incomplete valence shells based on their electron configurations.