Polyatomic Ions
Many of the ionic compounds we deal with in chemistry are called binary
compounds. They are called this because they consist of two different elements. In the
case of an ionic compound, one element is a monatomic cation, and the other, a
monatomic anion. NaCl, or sodium chloride, is a classic example. In class we have
learned how to write formulas and names for these types of compounds.
Ionic compounds can also be formed from polyatomic ions as well. A polyatomic ion
is an ion that is formed from a group of two or more nonmetal elements. The entire
group carries a specific charge and acts as one unit. A classic example of a compound
that contains a polyatomic ion is blackboard chalk, or calcium carbonate. The formula
for chalk is CaCO3, and consists of the monatomic cation calcium, Ca2+, and the
polyatomic anion CO32-, which is given the name carbonate. The entire CO3 carries the –
2 charge, and acts as a group just as Cl- does in sodium chloride.
Unfortunately, the only way to learn the polyatomic ions is by memorization and
practice. We will divide this exercise up into two parts. The first set of ions you must
know for Test III.. You are responsible for the second set by the time of our next quiz in
Nov after test III. This set can be found on page 127 of your text.
Polyatomic ions you need you need to know – Round I
Name
Formula
ammonium
NH4+
acetate
C2H3O2cyanide
CNhydroxide
OHoxalate
C2O42sulfite
SO32sulfate
SO42nitrite
NO2nitrate
NO3carbonate
CO32perchlorate
ClO4chlorate
ClO3chlorite
ClO2hypochlorite
ClOphosphate
PO43Phosphite
PO33=