A SUGGESTED CONVENTION FOR THE REPRESENTATION OF IONIC SUBSTANCES STANLEY G. SUNDERWlRTH Colorado State University, Fort Collins, Colorado
THErepresentation of ionic compounds by suitable formulas often confuses the beginning student of chemistry. I t is possible that some of this confusion is due to lack of uniformity among instructors in presenting ionic formulas. This could especially be true in the larger colleges where a student may have several instructors during a school year, possibly even more than one for the same course. The following conventions supply a systematic representation of ionic compounds. These conventions are not original with the author; they summarize ideas from several textbooks of general chemistry.' 1. For compounds which are known to exist primarily as ions in the solid state, nse a coefficient in front of the ions, which should be separated by a comma. Examples:
2. For ionic compounds in solution, use a coefficient in front of the ions and separate them with a plus sign. Examples: Ca++
+ 2N03-;
Na+
+ OH-
The solution of calcium nitrate in water would then be written .
. .
~ - - -
~~~
3. For compounds which are known t,o be primarily covalent, use the molecular convention. Examples: CO?; NHI
4. For the solution of covalent compounds which form ions in solution, use the molecular form on the left and the convention for ions in solution on the right. Example: &SOa
-
2Hf
+ SO.--
-
A neutralhation reaction would then he written: 2Na+
+ 2 0 H + 2H+ + S
O 4
2Na+
+ SO4-- + 2H,O
5. A precipitate which is known to be ionic should be written in the ionic form used for solids. Example: Ba++ +2C1-+2H+ +SO4---Ba++,SO+--4
+ 2H+ + 2CI-
6. Weak acids and bases should be written in the molecular form even in aqueous solution. Example: Alt+
3NOa-
+ 3NH*OH
-
AI(OH)a 4
+ 3NH,+ + 3NOr-
Notice that aluminum hydroxide is written in the molecular form.
It is realized that these rules will not meet with the annrnval of all inst,n~rt.ors. Nnr will t,hev arrnunt fnr
JOURNAL OF CHEMICAL EDUCATION
