Overview
This lecture covers how to name and memorize common polyatomic ions, including key rules for distinguishing between ions with similar names and using prefixes to determine their formulas.
What Are Polyatomic Ions?
- Polyatomic ions are groups of atoms bonded together with an overall charge.
- Examples include ammonium (NH₄⁺), sulfate (SO₄²⁻), chromate (CrO₄²⁻), chlorate (ClO₃⁻).
- There are 27 common polyatomic ions typically encountered in introductory chemistry.
Naming Rules and Patterns
- Ions ending in “-ate” have one more oxygen than their “-ite” counterparts.
- Example: Chlorate (ClO₃⁻) vs. Chlorite (ClO₂⁻).
- Bromate (BrO₃⁻) has one oxygen more than bromite (BrO₂⁻).
- Sulfate (SO₄²⁻) has one oxygen more than sulfite (SO₃²⁻).
- The rule also applies to nitrate/nitrite and iodate/iodite pairs.
Use of Prefixes: Per- and Hypo-
- The prefix “per-” indicates one more oxygen than the “-ate” form.
- Example: Perchlorate (ClO₄⁻) has one more oxygen than chlorate (ClO₃⁻).
- Perbromate (BrO₄⁻) > Bromate (BrO₃⁻).
- The prefix “hypo-” means one less oxygen than the “-ite” form.
- Example: Hypochlorite (ClO⁻) has one less oxygen than chlorite (ClO₂⁻).
Monatomic vs. Polyatomic Ions
- Ions ending in “-ide” (e.g., chloride, bromide, sulfide) are monatomic (single atom).
- Polyatomic ions typically end in “-ate” or “-ite”.
Memorization Tips
- Memorize the “-ate” versions of key polyatomic ions first.
- Use the “8 is bigger than ite” rule: “-ate” has more oxygen than “-ite”.
- Use prefixes “per-” (one more O) and “hypo-” (one less O) as needed.
Key Terms & Definitions
- Polyatomic ion — a charged group of covalently bonded atoms.
- Monatomic ion — an ion consisting of a single atom.
- -ate suffix — indicates a polyatomic ion with more oxygens.
- -ite suffix — indicates a polyatomic ion with one less oxygen than “-ate”.
- Per- prefix — one more oxygen than the “-ate” form.
- Hypo- prefix — one less oxygen than the “-ite” form.
Action Items / Next Steps
- Memorize the formulas and charges of the most common “-ate” polyatomic ions.
- Practice applying the “8 is bigger than ite” and prefix rules to related ions.
- Review any provided tables of polyatomic ions for upcoming quizzes or assignments.