Key Polyatomic Ions to Know for General Chemistry GCC Chemistry
First, and most importantly, MEMORIZE these 16 polyatomic ions…
2+ Cation 1+ Cations 0 1– Anions 2– Anions 3– Anions
– 2– 3– Hg2 2+ mercury(I)* NH4 + ammonium CN cyanide SO4 sulfate PO4 phosphate
+ – 2– H3O hydronium NO3 nitrate CO3 carbonate
– 2– OH hydroxide CrO4 chromate
– 2- N3 azide Cr2O7 dichromate
– 2– CH3COO O2 peroxide
– or C2H3O2 acetate
– MnO4 permanganate
– ClO3 chlorate
*In the diatomic mercury(I) ion, each mercury atom has lost one electron (for a charge of 2+ for the diatomic pair)
(Please see the next page for other polyatomic ions you need to know)
…and THEN use these three patterns to help you learn many more ions than you have memorized:
Pattern 1. Naming based on “ate”. Whenever a polyatomic anion ending in “-ate” has oxygens in it (“oxyanions”), there may be derivatives of that anion with a different number of oxygens. When this happens, the charge does not change. The regular pattern for naming these is as follows:
Change in # oxygens Prefix & Suffix becomes Example: Example: Example: chlorine based oxyanions nitrogen based oxyanions sulfur based oxyanions – +1 oxygen per- -ate ClO4 perchlorate – – 2- Starting at “-ate” -ate ClO3 chlorate NO3 nitrate SO4 sulfate – – 2- -1 oxygen -ite ClO2 chlorite NO2 nitrite SO3 sulfite – – -2 oxygens hypo- -ite ClO or OCl hypochlorite
Pattern 2. Group relationships. Often, elements within a group have the same number of oxygens in their “-ate” oxyanion (though charges are different). A notable exception to this pattern is nitrate, which has only three oxygens, even though others in its group have four:
Group 14 Group 15 Group 16 Group 17 Period “-ate” oxyanions “-ate” oxyanions “-ate” oxyanions “-ate” oxyanions 2- – 2 CO3 carbonate NO3 nitrate 2- 3- 2- – 3 SiO3 silicate PO4 phosphate SO4 sulfate ClO3 chlorate 3- 2- – 4 AsO4 arsenate SeO4 selenate BrO3 bromate 2- – 5 TeO4 tellurate IO3 iodate
Pattern 3. Hydrogen-containing polyatomic anions. When hydrogen is added to a polyatomic anion to make a new anion, it increases the charge by +1:
2– 2– 3– CO3 carbonate SO4 sulfate PO4 phosphate – – 2– HCO3 hydrogen carbonate HSO4 hydrogen sulfate HPO4 hydrogen phosphate (or bicarbonate**) (or bisulfate**) – H2PO4 dihydrogen phosphate
** The International Union of Pure and Applied Chemistry has recommended that use of the names bicarbonate and bisulfate be discontinued.
Remember: For simple MONOatomic anions…when a single atom becomes an anion by gaining one or more electrons, it takes an “-ide” ending to show that it is now a monoatomic anion, for example: N is nitrogen but N3- is nitride, O is oxygen but O2- is oxide, F is fluorine but F- is fluoride, H is hydrogen but H– is hydride.