Which rule states that atoms are most stable when their valence shell is full and that this can be achieved by bonding with other atoms?

• A. Octet rule
• B. Metals
• C. Atomic radius
• D. Ionization energy

Answer: (A)

Atoms are most stable when their outermost electron shell is filled. This leads to the octet idea: having eight electrons in the valence shell gives a configuration similar to noble gases, which are particularly stable. To reach that full shell, atoms tend to gain, lose, or share electrons through bonding with other atoms. When they share electrons, covalent bonds form and help complete the valence shell; when they transfer electrons, ionic bonds do the job, giving each participating atom a full outer shell. The octet rule is a useful guide for understanding why many elements form the typical bonding patterns you see in molecules and compounds. Some elements, like hydrogen and helium, achieve stability with two electrons, but the general emphasis is on filling the valence shell to attain a stable arrangement. The other terms describe types of elements or measured properties—metals are a class of elements, atomic radius is about size, and ionization energy is the energy required to remove an electron—rather than a rule about attaining stability through a full valence shell.