Key Concepts: Writing Correct Formulas

Core Definitions

• Chemical Formula: Uses element symbols and subscripts to show the composition of a compound (e.g., H₂O).
• Cation: A positively charged ion formed when an atom loses electrons.
• Anion: A negatively charged ion formed when an atom gains electrons.
• Criss-Cross Method: Use the charge of each ion as the subscript of the other to write formulas.
• Polyatomic Ion: A group of atoms bonded together that carry a charge (e.g., SO₄²⁻, NH₄⁺).
• Neutral Compound Rule: The total positive charge must equal the total negative charge in a formula.