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 Polyatomic Ions

 

Polyatomic Ions-A polyatomic ion is a molecule made up of 2 or more atoms that bears ionic groups, that is, a molecule with a charge.

Oxyanions- Negative polyatomic ions with oxygen

Prefix Suffix Example Names
Per- (more than) -ate (largest #) ClO4- perchlorate
  -ate (large #) ClO3- chlorate
  -ite (smaller #) ClO2- chlorite
Hypo- (less than) -ite (smallest #) ClO- hypochlorite

Other important polyatomic ions (from-http://www2.pvc.maricopa.edu/tutor/chem/chem130/nomenclature/polyatomicion.html)

 Tips to memorize your polyatomic ions.

Determining the charge of a polyatomic ion

Polyatomic ions exist because the atoms contained in them with stable electron configurations. These are even number of electrons. If the total of the group numbers of the atoms is odd, it will need an odd number of electrons to make the total even. Therefore if the total is an odd #, the charge of the ion is 1- (phosphate is the only 3- you need to know).  If the total of all the group numbers is even then the charge is also even. The charge would be 2-. 

 

Common Polyatomic Ions

+1 CHARGE -1 CHARGE -2 CHARGE -3 CHARGE -4 CHARGE
ion name ion name ion name ion name ion name
NH4+ ammonium H2PO3- dihydrogen phosphite HPO32- hydrogen phosphite PO33- phosphite P2O74- pyrophosphate
H3O+ hydronium H2PO4- dihydrogen phosphate HPO42- hydrogen phosphate PO43- phosphate    
Hg22+ mercury(I) HCO3- hydrogen carbonate CO32- carbonate PO23- hypophosphite    
    HSO3- hydrogen sulfite SO32- sulfite AsO33- arsenite    
    HSO4- hydrogen sulfate SO42- sulfate AsO43- arsenate    
    NO2- nitrite S2O32- thiosulfate        
    NO3- nitrate SiO32- silicate        
    OH- hydroxide C22- carbide        
    CH3COO- acetate C2O42- oxalate        
    CrO2- chromite CrO42- chromate        
    CN- cyanide Cr2O72- dichromate        
    CNO- cyanate C4H4O62- tartrate        
    CNS- thiocyanate MoO42- molybdate        
    O2- superoxide O22- peroxide        
    MnO4- permanganate S22- disulfide        
    ClO- hypochlorite            
    ClO2- chlorite            
    ClO3- chlorate            
    ClO4- perchlorate            
    BrO- hypobromite            
    BrO2- bromite            
    BrO3- bromate            
    BrO4- perbromate            
    IO- hypoiodite            
    IO2- iodite            
    IO3- iodate            
    IO4- periodate            
    AlO2- aluminate            
    N3- azide      

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