Multivalent Metals  Some metals can have more than one valence number and are able to form more than one type of ion.  Example: Iron has a valence of 2 or 3 and so can become either the ion Fe +2 or Fe +3.

 When naming these ionic compounds, the name must include a Roman numeral after the metal name to indicate the ion type.  Example: Fe 2 O 3 is iron III oxide  FeO is iron II oxide

Polyatomic Ions BFF’s

Polyatomic Ions  Polyatomic ions are groups of atoms that tend to stay together and carry an overall ionic charge.  The group of atoms acts like a single ion.

B.F.F’s  POLYATOMIC ATOMS ARE BEST BUDDIES They are ALWAYS TOGETHER!!!!

 Polyatomic ions can combine with other ions (like the single atoms from earlier in the lesson) to form polyatomic compounds.

Polyatomic Ions

WRITING FORMULAS FOR POLYATOMIC COMPOUNDS  Since polyatomic ions have charges, they will form ionic compounds just like regular ions.  To form a polyatomic compound, follow the exact same steps used with simple ionic compounds studied earlier.

 Example: Chalk is made up of calcium and carbonate. What is the formula of chalk? Always write the positive ion first followed by the negative ion. Use the Cross-over rule again.

 Why are brackets needed here? Because (CO 3 ) is a separate unit, the brackets mean that there are 2 (CO 3 ) ions in this compound  We can reduce it to lowest terms: Ca(CO 3 )

NAMING POLYATOMIC COMPOUNDS  Follow these rules:  The metal ion is named first. Use the name found on the periodic table.  Name the non-metal ion second, using the name from the chart above. The ending of polyatomic ions is never changed!!!

The Exception!!!  ***Ammonium is the only polyatomic which is a positive ion and it follows the same rules as other positive ions.

 Try the examples on your hand-out!