Chemical Formulas & Chemical Compounds Writing and Naming Formulas For Ionic Compounds with Polyatomic ions

Objective Learn how to write and name compounds with polyatomic ions

Ionic Compounds containing Polyatomic ions Some ionic compounds contain polyatomic ions. Groups of atoms that are covalently bonded and have a charge.

Polyatomic Ions Most polyatomic ions are anions Most of these are oxyanions –Contain oxygen Sometimes a group of elements can form more than one oxyanion

Common Polyatomic ions

What’s up with the ate and ite? Ex: PO 4 -3 and PO 3 -3 The greater number of oxygen atoms – ends in “ate” (PO 4 -3 phosphate) The fewer number of oxygen atoms – ends in “ite” (PO 3 -3 phosphite)

Name these Polyatomic ions NO 3 -1 SO 4 -2 SO 3 -2 NH 4 +1 this is the only polyatomic cation

Write formulas with polyatomic ions Look at the ions and balance their charges, create the formula. (The easiest way to balance charges is to criss cross them) If there is more than one polyatomic ion in the formula put ( ) around it and the subscript for the polyatomic ion on the outside of the ( ). Ex: Mg +2 PO 4 -3 Mg 3 (PO 4 ) 2

Write formulas with polyatomic ions Mg +2 PO 4 -3 Mg +2 (PO 4 ) -3 Mg 3 (PO 4 ) 2

Try another one K +1 NO 3 -2 K +1 (SO 3 ) -2 K 2 (SO 3 ) 1 you don’t need to write the ( ) or #1 K 2 SO 3

Write these formulas Li +1 NO 3 -1 Mg +2 SO 4 -2 Ca +2 SO 3 -2 Na +1 PO 4 -3 Al +3 HCO 3 -1

Naming Ionic Compounds with Polyatomic Ions Just like in monatomic ionic compounds, NAME THE CATION WITH THE ELEMENTS NAME NAME A MONOATOMIC ANION BY CHANGING THE ENDING TO “ide” The polyatomic ion has its own name and that DOES NOT CHANGE Ex: Li +1 NO 3 -1 LiNO 3 lithium nitrate

Naming Ionic Compounds with Polyatomic Ions Ca(HCO 3 ) 2 This compound comes from the Ca +2 ion and the HCO 3 -1 ion Ca(HCO 3 ) 2 calcium hydrogen carbonate Just name the parts. No Name Changes

You Try NH 4 NO 3 (Hint: this compound has two polyatomic ions) Sr 3 (PO 4 ) 2 Zn(NO 2 ) 2 MgCO 3 Answers will be given in class