H2O vs OH2
Name: George N.
Date: 2001 - 2002
A fellow teacher asked me a question a student inquired
of him. I hope you can help us out. The question was "Why is the
formula for water H2O and not OH2?"
It is conventional to write the more electropositive element in a compound
first and the more electronegative element last -- so NaCl rather than ClNa.
Having said that sometimes it is not all that clear, for example iodine
monochloride is written ICl rather than ClI. I doubt that any chemist would
be confused if you wrote OH2 rather than H2O.
Hi, George !!
During the development of the chemistry
there were a number of symbols used
by the chemists. Nowadays, the modern
way to write the water is H2O.
The positive charged ion remains on the
left side and the negative charged ion
remains on the right side of the molecule.
So, instead of SO4H2, you set down H2SO4.
Water is represented by H2O.
It is all a matter of convention. For simple molecules such as water, the
convention is to list the more electropositive elements first and the more
electronegative elements later - H2O, NaCl. This basic principle is also
used for ionic compounds in which the anion and/or cation are composed of
many atoms - LiClO4, NH4Cl. Other conventions are used, however. Organic
compounds are usually listed as carbon, then hydrogen, followed by all the
other elements in alphabetical order of element symbol.
Any chemist will, however, recognize OH2 as water. In fact, any chemist
will also be able to give examples of situations in which it would make
sense to write the formula for water as H2O.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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Update: June 2012