Ions may also be polyatomic, that is, they may contain more than one atom. These atoms are covalently bonded to one another. The structure of three polyatomic anions and a polyatomic cation are shown below.
The corresponding -ite ions have the same overall charge but have one fewer oxygens.
Other polyatomic -ate ions result from combination of H+ an anion (O2– or CO3 2–).
CO32–
carbonate
NO3–
nitrate
SO42–
sulfate
PO43–
phosphate
carbonate
NO3–
nitrate
SO42–
sulfate
PO43–
phosphate
Nitrate, sulfate and carbonate and phosphate are examples of oxoanions. Oxoanions have a central atom surrounded by either three or four oxygen atoms. The oxygen of the structural element =O is referred to as an oxo group.
Chemists usually represent oxoanions either by their formulae or by their name.
Note that the names of the oxoanions
Chemists usually represent oxoanions either by their formulae or by their name.
Note that the names of the oxoanions
- contain all (for example, carbon) or part (for example, sulf) of the name of the central element.
- end in -ate.
Contrast this with the names of the monatomic anions that end in -ide (Cl– is chloride, for example).
nitrite is NO2–
sulfite is SO32–
sulfite is SO32–
Other polyatomic -ate ions result from combination of H+ an anion (O2– or CO3 2–).
Hydroxide (usually written OH–) results from H+ combining with O2–. It may be more appropriate to write HO–.
In hydrogencarbonate (HCO3–) the extra hydrogen is also bonded to one of the oxygens that was negative in CO32– .
In hydrogencarbonate (HCO3–) the extra hydrogen is also bonded to one of the oxygens that was negative in CO32– .