8-3 Names and Formulas for Ionic Compounds

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8-3 Names and Formulas for Ionic Compounds

• P.221-227

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Objectives

• Write formulas for ionic compounds and oxyanions
• Name ionic compounds and oxyanions

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Key Terms

• Polyatomic ion
• Oxyanion

• Formula unit
• Monoatomic ion
• Oxidation number

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Formulas for Ionic Compounds

• A formula unit simplest ratio of ions
  representing a compound
• ALL ionic compounds are written as formula units
  (not the case for covalent compounds)

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Monoatomic Ions

• Monoatomic ions contain a single element
• Be2, Na, Fe3
• Notice the charge on the elements!

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Polyatomic Ions

• Polyatomic ions have more than one element, with
  a net charge
• SO42-, NH4, NO2-, C2H3O2-
• Treat like a single unit, not individual ions

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Naming Binary Ionic Compounds

• Step 1 Name the cation first and the anion
  second.
• Step 2 Monoatomic cations use the element name.
• Step 3 Monoatomic anions use the ion name with
  the ide ending.
• Step 4 For d-block cations you must write the
  cation charge as a roman numeral in parentheses.
• Step 5 If the compound contains a polyatomic
  ion, just use the name of the ion.

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Naming Binary Ionic Compounds

• Example
• NaCl Sodium Chloride
• FeO Iron (II) Oxide
• NH4Cl Ammonium Chloride

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Writing a Chemical Formula from the Name

• Step 1 Write the element symbol for name of the
  ion
• Step 2 Write the charge of the ion
• Step 3 If the total charge equals zero, you are
  done. If the total charge does not equal zero,
  you must change the subscripts so that the total
  charge equals zero (drop-n-cross).

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• Writing a subscript for a polyatomic ion put a
  parenthesis around it with the subscript on the
  outside of the parenthesis
• Example Cr(SO4)2

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• Example Barium Fluoride
• Step 1 Ba F
• Step 2 Ba2F-
• Step 3 Total charge 1
• Step 4 BaF2

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• Example Iron (III) Sulfate
• Step 1 Fe SO4
• Step 2 Fe3SO42-
• Step 3 Total charge 1
• Step 4 Fe2(SO4)

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• Example Beryllium Oxide
• Step 1 Be O
• Step 2 Be2O2-
• Step 3 Total charge 0 ? BeO

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Homework

• P.227 35-36,38-39
• P.237 74-79