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Unit Information
Nomenclature and formula writing corresponds to chapter 6 in the text Foundations of College Chemistry by Hein and Arena.
Hints
  • In nearly all cases, the more positive element/ion is given first in the formula.
  • Organic formulas are often written in a manner to simplify drawing the structural formula.  As a result, many organic anions are written first.
  • Anions that are derived from elements have their endings changed to -ide.
  • Covalent compounds are made of two elements and none can be a metal.
  • Covalent compounds use the prefixes to indicate the number of each element in the compound.
  • Inorganic acids have formulas that begin with H.
  • Organic acids have formulas that contain COOH
  • Acids that are derived from elements begin with the prefix hydro-.
  • Acids derived from polyatomic ions that end in -ate use the suffix -ic.
  • Acids derived from polyatomic ions that end in -ite use the suffix -ous.
  • HCN is hydrocyanic acid.  It is the only polyatomic ion derived acid that uses hydro-.
  • Ionic compounds are named by naming the cation and then the anion.
  • If the cation in an ionic compound is a polyatomic ion, Group 1 through 3, Group 13, Zn, Cd, or Ag − no Roman numeral is needed to indicate charge.
  • Ammonia is the compound NH3, ammonium is the polyatomic ion NH4+.
Mercury Ions
Mercury has two oxidation states, or charges.  They are mercury (I) and mercury (II).  While this may imply that the corresponding symbols for these ions are Hg+ and Hg2+ respectively, this is not the case.  The mercury (I) ion is found as Hg22+ which at first glance seems impossible.  However, the "2+" charge for a mercury (I) ion is possible because there are two mercury ions linked together.  Therefore, the total charge of two mercury ions is +2, making the value for each ion a +1.
Polyatomic Ions
There are some tricks for certain polyatomic ion "families."  Take a look at the examples below:
per- root -ate periodate IO4-    
root -ate iodate IO3- sulfate SO42-
root -ite iodite IO2- sulfite SO32-
hypo- root -ite hypoiodite IO-    
The above examples should show you the relationship between certain prefix/suffix combinations and the number of oxygens in the corresponding polyatomic ion.  The charge does not change, only the number of oxygens.  As is the case with sulfate (and many others), not all four ions exist, although it is possible to predict the name and charge.
There is another rule for ions that begin with the prefix "bi" or the word "hydrogen."  Firstly, in this context the two are synonyms of each other.  This means that bicarbonate and hydrogen carbonate refer to the same ion.  The relationship for the ion carbonate is shown below: 
carbonate CO32- bicarbonate/hydrogen carbonate HCO3-  
sulfate SO42- bisulfate/hydrogen sulfate HSO4-  
The addition of a hydrogen (+1 ion) will raise the charge by 1.  In the case of carbonate, its original -2 charge, when added to the +1 of hydrogen, becomes a -1 (+2 + -1) ion.

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Last update: Monday, June 21, 2010