Ionic Compounds Naming/Formula Writing Polyatomic ions Chapter 4.2 Ionic Compounds Naming/Formula Writing Polyatomic ions

Polyatomic Ions A polyatomic ion is a group of atoms, usually of different elements, that together have an overall charge. Example: NO3- Nitrate SO42- Sulfate PO43- Phosphate

NOTICE: They are part of ionic compounds The name of a polyatomic ion usually has the ending –ate or –ite Polyatomic ions usually have a negative charge except ammonium which is NH4+ *****see the list of all of polyatomic ions*****

Naming Rules 1. Name the metal. a) If the metal is multivalent, use a roman numeral in brackets after the metal name to indicate the charge of the ion. b) If NH4 is present write its name ammonia 2. Name the non-metal a) Write the name of the negative polyatomic ion as it is shown on your list OR b) Write the name of your non-metal and change the ending to -ide

Examples – Name the following compounds LiOH Mg3(PO4)2 Al2(SO3)3 NH4S

Examples – Naming compounds with multivalent metals and polyatomic ions Fe2(SO3)3 CuOH Mn(PO3)3 NiCO3 You must mathematically determine the charge on the metal

Writing the formula of an Ionic compound with a polyatomic ion Rules Write the symbol of the metal/polyatomic ion with its ion charge as a superscript Write the symbol of the non-metal/polyatomic ion with its ion charge as a superscript Criss cross the charges so that they become subscripts for the opposite element and remove + or – signs Use brackets around polyatomic ions if there is more than one ion after criss crossing Simplify the subscripts if possible.

Example of formula writing Potassium nitrate Magnesium sulfate Ammonium phosphite

Examples of formula writing Copper (II) sulfite Chromium (VI) hydroxide Cobalt (III) permanganate

Homework Worksheet “Polyatomic Ions Naming and Formula Writing”