Overview
This lecture covers the names, formulas, and patterns of common polyatomic ions, highlighting how to memorize and distinguish between them for chemistry courses.
Introduction & Importance
- Memorizing polyatomic ions is essential for writing formulas, balancing equations, and success in chemistry.
- Polyatomic ions are ions with multiple atoms; monoatomic ions have only one atom.
Naming Patterns & Examples
- Polyatomic ions ending in "ate" have one more oxygen than those ending in "ite".
- Monoatomic ions usually end in "ide" and typically lack oxygen.
- Adding hydrogen to a polyatomic ion changes the name (e.g., hydrogen sulfate, dihydrogen phosphate).
- Prefixes indicate oxygen count: "per" (one more O), "hypo" (one less O).
Common Polyatomic Ions
- Nitrate (NO₃⁻), Nitrite (NO₂⁻), Nitride (N³⁻)
- Sulfate (SO₄²⁻), Sulfite (SO₃²⁻), Sulfide (S²⁻)
- Phosphate (PO₄³⁻), Phosphite (PO₃³⁻), Phosphide (P³⁻)
- Chloride (Cl⁻), Chlorite (ClO₂⁻), Chlorate (ClO₃⁻), Perchlorate (ClO₄⁻), Hypochlorite (ClO⁻)
- Corresponding patterns hold for bromine (Br) and iodine (I) ions.
Hydrogen-Containing Polyatomic Ions
- Hydrogen carbonate (HCO₃⁻)/Bicarbonate
- Hydrogen sulfate (HSO₄⁻)/Bisulfate, Hydrogen sulfite (HSO₃⁻)/Bisulfite
- Hydrogen phosphate (HPO₄²⁻), Dihydrogen phosphate (H₂PO₄⁻)
- Each added hydrogen increases the charge by +1.
Other Important Polyatomic Ions
- Hydroxide (OH⁻), Ammonium (NH₄⁺)
- Acetate (C₂H₃O₂⁻), Oxalate (C₂O₄²⁻)
- Chromate (CrO₄²⁻), Dichromate (Cr₂O₇²⁻)
- Permanganate (MnO₄⁻), Thiosulfate (S₂O₃²⁻)
- Cyanide (CN⁻), Thiocyanate (SCN⁻)
Special Cases & Exceptions
- Some ions with "ide" endings (e.g., cyanide, hydroxide) are polyatomic.
- Oxygen has several ion forms: Oxide (O²⁻), Peroxide (O₂²⁻), Superoxide (O₂⁻)
- Azide (N₃⁻) differs from Nitride (N³⁻)
- Borate (BO₃³⁻), Hydronium (H₃O⁺)
- Pyrophosphate (P₂O₇⁴⁻) is important in biochemistry.
Key Terms & Definitions
- Polyatomic ion — an ion composed of two or more atoms bonded together.
- Monoatomic ion — an ion consisting of a single atom.
- "Ate"/"ite" — suffixes indicating the number of oxygen atoms; "ate" has more than "ite."
- Hydrogen carbonate — HCO₃⁻, also called bicarbonate.
- Hydroxide — OH⁻, a polyatomic ion with oxygen and hydrogen.
- Ammonium — NH₄⁺, a polyatomic cation.
- Thiosulfate — S₂O₃²⁻, a sulfur-containing polyatomic ion.
- Per, hypo — prefixes to indicate more or fewer oxygens.
Action Items / Next Steps
- Memorize the names and formulas of common polyatomic ions, focusing on patterns and exceptions.
- Practice writing formulas from given names and vice versa.
- Complete any assigned quizzes or worksheets on polyatomic ions.