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Chemical Formulas & Chemical Compounds
Writing and Naming Formulas For Ionic Compounds with Polyatomic
ions
ObjectiveLearn 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: PO4-3 and PO3
-3
• The greater number of oxygen atoms – ends in “ate” (PO4
-3 phosphate)
• The fewer number of oxygen atoms – ends in “ite” (PO3
-3 phosphite)
Name these Polyatomic ions
• NO3 -1
• SO4 -2
• SO3-2
• NH4+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 PO4-3 Mg3 (PO4)2
Write formulas with polyatomic ions
Mg+2 PO4-3
Mg+2 (PO4)-3
Mg3 (PO4)2
Try another one
K+1 NO3-2
K+1 (SO3)-2
K2 (SO3)1 you don’t need to write the ( ) or #1
K2 SO3
Write these formulas• Li+1 NO3 -1
• Mg+2 SO4 -2
• Ca+2 SO3-2
• Na+1 PO4-3
• Al+3 HCO3-1
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 NO3 -1 LiNO3
lithium nitrate
Naming Ionic Compounds with Polyatomic Ions
• Ca(HCO3)2
• This compound comes from the Ca+2 ion and the HCO3
-1 ion
• Ca(HCO3)2
• calcium hydrogen carbonate
• Just name the parts. No Name Changes
You Try• NH4 NO3 (Hint: this compound has two polyatomic ions)
• Sr3(PO4)2
• Zn(NO2)2
• MgCO3
Answers will be given in class