c. There are several significant exceptions to the rules for the naming of anionic
radicals. The most important is the previously mentioned carbonate radical (CO3 -2).
Several others bear mentioning because you are likely to see them in medicine.
(1) Certain radicals are derived when hydrogen is removed from an acid to
form a charge group of atoms (radical). If one hydrogen is removed, the radical gets the
prefix "bi." This indicates that one hydrogen is missing.
(a) Example 1: When carbonic acid (H2CO3) gives up one hydrogen
ion, it loses a positively charged hydrogen atom. It becomes a radical HCO3 -1 and is
assigned the name bicarbonate. "Bi" indicates one hydrogen was removed.
(b) Example 2: H2PO4 -1 is called the biphosphate radical because it
was derived from phosphoric acid (H3PO4) by removing one hydrogen atom.
(2) Several radicals do not follow any of the above rules. Their names and
formulas must be memorized. Some of the most common are hydroxide (OH -1),
peroxide (O2 -2), and thiosulfate (S2O3 -2).
(3) Occasionally, metals with valences higher than +1 will form salts that
contain oxide or hydroxide ion. When these occur in the middle of the formula, they are
referred to as either oxy- or hydroxy-, respectively. Number prefixes are used to denote
the number of them.
1-13. NAMING SALTS
A salt is an ionic compound containing some cation other than hydrogen and
some anion other than hydroxide and oxide. Since the compound must be electrically
neutral, the total positive valence (from all of the cations) must equal the total negative
valence (from all the anions). This gives us a method for determining the valence of
any particular ion in the formula. The names for salts are made by writing the name of
the cation followed by the name of the anion. For example, CaCl2 has calcium as the
cation and chloride as the anion, so the compound is called calcium chloride. FeSO4
has sulfate as the anion, but we need to know whether the ion is ferrous ion or ferric ion.
This is easy for us to do: since we know the total negative valence (from sulfate) is -2,
the total positive valence (for iron) must be +2; therefore, it is ferrous ion. The
compound is ferrous sulfate.