Key Concepts: Valence Electrons & Reactivity

Core Definitions

• Valence Electrons: Electrons in the outermost energy level; determine an element's chemical behavior.
• Octet Rule: Atoms tend to gain, lose, or share electrons to have 8 valence electrons (stable).
• Alkali Metals (Group 1): Have 1 valence electron; very reactive, easily lose 1 electron.
• Halogens (Group 17): Have 7 valence electrons; very reactive, easily gain 1 electron.
• Noble Gases (Group 18): Have 8 valence electrons (full outer shell); very stable and unreactive.
• Reactivity Trends: Metals become more reactive going down a group; nonmetals become more reactive going up.