Atoms achieve stability by having a completely filled outermost electron shell (also called the valence shell). This is often referred to as following the octet rule, which states that atoms are most stable when they have 8 electrons in their outer shell (like the noble gases).
Ways atoms achieve stability:
- By gaining electrons (to form anions):
- Nonmetals like chlorine or oxygen gain electrons to complete their octet.
- Example: Cl gains 1 electron → Cl⁻.
- By losing electrons (to form cations):
- Metals like sodium or magnesium lose electrons to empty their outer shell, exposing a stable inner shell.
- Example: Na loses 1 electron → Na⁺.
- By sharing electrons (to form covalent bonds):
- Two atoms share pairs of electrons so both can complete their octet.
- Example: In H₂O, oxygen shares electrons with hydrogen.
- By forming metallic bonds:
- Metal atoms share a “sea of electrons” that makes them stable and conductive.
Key Idea: Stability is reached when atoms have electron arrangements similar to the nearest noble gas configuration.