Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Chemical formula questions 
Name:  Lisa Malone
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: 1999
Question:
What is the chemical formula for ammonium dichromate? When are parentheses used in writing chemical formulas?


Replies:
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...

-Joe Schultz


Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory