Module 4: PART D: BINARY (IONIC) COMPOUNDS
The element written first in either the name or the formula is a metal. The element written second is a nonmetal. Salts are metallic and nonmetallic ionic compounds. There are no molecules of salts-just macro ionic lattices. Name the metallic element. If the metallic element has more than one ionic state, write a ROMAN NUMERAL after the elementís mane to indicate which charge state the metallic element is using to form the compound.
Drop the suffix off the nonmetalís name and add -ide which indicates the salt is binary
(exceptions: cyanide & hydroxide which are polyatomic ions).
No prefixes are used to indicate how many atoms are present in the formula.
NaCl Sodium Chloride (table salt)
Al2O3 Aluminum oxide
Fe2O3 Iron III oxide (rust)
To write the formula from the name of the salt use the following procedure:
(a) Write the symbols
(or formulas for radicals) of the ions represented
(a) Ca N
(b) Use the periodic chart to write the ion charge of each element (or polyatomic ion) as superscripts:
(c ) Find the L.C.M. (Least common multiple) of the positive and negative charge.
The LCM is the smallest number that both charges will decide into evenly. The LCM is the total electrons transferred. Therefore, it represents the total positive charge created by the metallic ions and the total negative charge created by the nonmetallic ions. This may be proved by drawing the dot structure of the compound showing all electrons transferred.
The LCM of +2 and -3 is 6, therefore 6 e-1 are transferred creating a total positive charge of +6, and the total negative charge of -6
†††††† --> 6e-1-->
Ca+2 ††††††††† N-3
(d (d) Divide the LCM by the positive charge, this dividend will represent the subscript behind the metallic ion in the formula.
+6 divided by +2 = 3; therefore half of the formula is: Ca3Nx
(e) Divide the LCM by the negative charge, this dividend will represent the number of nonmetallic ions in the formula.
-6 divided by -3 = 2; therefore the other half of the formula is: Ca3N2
Example: Potassium phosphide
K+1 P -3
† LCM: 3
Balance the chemical formula:
In addition to working the sample tests, you may want to practice on writing the names and formulas for Ionic Compounds.
On Corwin pages 188-9, questions 13 thru 42 are also good practice.
You must complete the online homeworks:
D. Binary Ionic Names:
D1. Binary Ionic Formulas: