Polyatomic Compounds O A polyatomic ion is two or more atoms COVALENTLY bonded together that now act as if they were a SINGLE atom. However, due to the way these atoms bond, all polyatomic ions have a CHARGE. O This COVALENT bond holds the polyatomic ion together and then because it has a charge, it forms IONIC bonds with other ions.

Polyatomic Compounds O If the polyatomic ion is positive, it forms a bond with a negative ION (ANION) or negative polyatomic ion. O If the polyatomic ion is negative, it forms a bond with a positive ION (CATION) or positive polyatomic ion. O Most polyatomic ions end with “ATE” or “ITE”. The only exceptions are AMMONIUM and HYDROXIDE. *These can be found on your periodic table.

Atoms in a polyatomic atom are joined together by a covalent bond.

Polyatomic Nomenclature 1. Positive ions are always written first. 2. Usually end in “ate” or “ite”. 3. No prefixes. 4. Charges are crossed and written as a subscript to balance the ions charges. 5. A parenthesis may be placed when a subscript is needed. 6. The subscript is written outside the parenthesis.

Most Common Polyatomic Ions

Ex. Sodium and Phosphate Symbols: Na and PO 4 Charges: (+1) (-3)  Na +1 + PO 4 -3 Crisscross: Na 3 (PO 4 ) 1 = Na 3 PO 4 (Simplify when possible) Chemical Name: Sodium Phosphate Chemical Formula: Na 3 PO 4 Common Uses: Food preserve

Closure

Homework O Polyatomic Compounds: Names and Formulas Worksheet O Quiz: Nomenclature of Polyatomic Compounds – W4, D4