Key Concepts: Monatomic & Diatomic Gases

Core Definitions

• Monatomic Gas: A gas made of single atoms (e.g., noble gases: He, Ne, Ar, Kr, Xe, Rn).
• Diatomic Gas: A gas made of molecules with two atoms bonded together.
• Seven Diatomic Elements: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂ — remember HONClBrIF.
• Noble Gases: Monatomic; full outer shells make them stable and unreactive.
• Diatomic in Equations: Always write diatomic elements as molecules (e.g., O₂, not O) in chemical equations.
• Most Abundant Gas: Nitrogen (N₂) makes up about 78% of Earth's atmosphere.