Chemical formula questions
Name: Lisa Malone
What is the chemical formula for ammonium dichromate? When are parentheses
used in writing chemical formulas?
Ammonium dichromate: (NH4)2Cr2O7
Parentheses are used when there are more than one polyatomic
"functionalities" in a molecule and the formula has to be written out.
The example above shows this. The ammonium ion (four hydrogens connected
to one nitrogen which has an overall charge of +1) charge has to offset
the -2 charge of the dichromate ion. Since two ammoniums are needed,
and there's already a 4 as a subscript, the parentheses are used and the
2 goes outside. Otherwise it would look like NH42. Sound confusing?
Maybe someone else can word this better...
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Update: June 2012