True or False? Stable atoms have their outer electron shells completely filled.

• A. True
• B. False
• C. Only in gases
• D. Only in solids

Answer: (A)

Stable atoms indeed typically have their outer electron shells completely filled. This concept is rooted in the understanding of atomic structure and the octet rule, which states that atoms tend to be most stable when they have eight electrons in their valence shell. Atoms achieve stability through various means, such as forming bonds with other atoms to either share or transfer electrons, allowing them to complete their outer shell.

For example, noble gases, which are elements in Group 18 of the periodic table, naturally possess filled outer shells and exhibit very low reactivity. In contrast, elements with partially filled outer shells tend to be more reactive as they seek to either gain, lose, or share electrons to fill their valence shells.

The other choices indicate conditions that are not universally applicable to the stability of atoms. Stability through a filled outer shell is not confined to gases or solids; it applies to atoms across different states of matter. Therefore, the assertion that stable atoms have their outer electron shells filled aligns perfectly with the principles of atomic theory.