Writing Formulas and Names for Ionic Compounds

I can write the name and formula for a binary ionic compound.  A binary ionic compound is a compound made up of two types of elements ( a metal and a non-metal)  Examples include sodium chloride (NaCl) and Iron (III) oxide (Fe 2 O 3 )  Ionic formulas show the ratio of positive ions to negative ions in the substance.  The ratio must be just right so that the total positive charge will balance the total negative charge. The sum of the charges must equal zero.

Writing Formulas  1. Look up the charge (oxidation number) of the cation and the anion.  2. If the sum of the charges is zero, write the symbol for the metal followed by the symbol for the nonmetal.  3. If the sum of the charges is not zero, use a subscript on either or both elements to balance the charge. Always write the symbol for the metal first.  Examples  Write the formula for magnesium chloride, aluminum oxide and sodium sulfide  MgCl 2, Al 2 O 3, Na 2 S

Writing Names, when given the formula  1. Write the name of the cation.  2. Write the name of the anion, but drop the standard ending and add “ide”.  Examples: Write the name of NaF, Ca 3 N 2, K 2 S  Sodium fluoride, Calcium nitride, potassium sulfide

Writing formulas with transition metals, given the name.  1. The name will include a roman numeral. The Roman numeral is the charge on the cation.  2. Look up the charge on the anion.  3. If the sum of the charges is not zero, use subscripts on either or both elements to balance the charge.  Examples: Write the formula for Copper (II) oxide and Iron(III) Chloride  CuO, FeCl 3

Writing names transition metals, when given the formula.  1. Write the name of the cation (transition metal)  2. You MUST use a Roman numeral that represents the charge in the name except-  A. Zinc, Cadmium- always use 2+  B. Silver- always use 1+  C. Scandium, Yttrium- always use 3+  3. For all other transition metals, use the charge on the anion(s) to determine the charge of the transition metal. The sum of the charges must equal zero!  4. Write the name of the anion, but drop the standard ending and add “ide”.  Ex: PbCl 2, CuO Fe 2 O 3  Lead (II) chloride, Copper (II) oxide Iron (III) oxide

Writing formulas with POLYATOMIC IONS  Polyatomic ion- a charged group of atoms that are chemically bonded together.  OH -1 hydroxide  SO 4 -2 sulfate  CO 3 -2 carbonate  Use the charge on cation and anion to determine the subscript for each element or polyatomic ion.  Sodium hydroxide  Aluminum sulfate  Potassium carbonate If you need to add a subscript to a polyatomic ion, use a parenthesis, ex: Magnesium hydroxide- Mg(OH) 2

Writing names of compounds that contain polyatomic ions.  Write the name of the cation, usually the metal.  Exception- Ammonium- NH 4 +1 is the only polyatomic cation  Write the name of the anion, usually the polyatomic ion.  Use the chart to find name and formulas for polyatomic ions.  Examples:  (NH 4 ) 2 SO 4  Al(OH) 3  Cu(OH) 2