IUPAC Name and Formula of Anions Introductory Chemistry Tutorial
- An anion is a negatively charged ion.
- An anion can be composed of:
⚛ one atom (monoatamic anion)
⚛ more than one atom (polyatomic anion)
- The formula of a monoatomic(1) anion is made up of two parts:
Formula of Monoatomic Anion symbol of element charge as a superscript(2) to the right of the symbol E x-
Note the charge on the anion is given with the number first followed by the minus sign.
Ex- NOT E-x
- The charge on a monoatomic anion of a non-metal element can be determined from its location in the periodic table of the elements.
The table below gives the symbol of non-metal elements and the charge of the respective anions:
Groups of the Periodic Table Group 14
Period 2 C
Period 3 P
Period 4 Se
Period 5 I
Charge on Anions in Group 4- 3- 2- 1-
Hydrogen (H), period 1, can also form an anion with a charge of 1-
- The name of a monoatamic anion is made up of three parts:
(i) modified name of the element
(ii) "ide" substituted for the end of the name
(iii) charge on the anion given in parentheses (x-)
Acceptable IUPAC Name
of Monoatomic Anion
prefix ide (charge on anion) modified name of element ide (x-)
Note there is no space between the modified name of the element and the "ide" suffix nor is there a space between the "ide" and the parentheses enclosing the charge on the anion:
elemide(x-) NOT elem ide(x-) NOT elemide (x-)
Note that the charge in parentheses (x-) may be omitted if there is no ambiguity in the name.
- The name of the element present in the anion is modified by removing the end of the element's name.
Examples of the ends of non-metal element names that get removed are:
removable ending Non-metal Examples Element Name Modified Name ine fluorine fluor chlorine chlor bromine brom iodine iod ium selenium selen ogen hydrogen hydr nitrogen nitr on carbon carb orus phosphorus phosph ur sulfur sulf ygen oxygen ox
- You may be expected to know the name and formula of some polyatomic anions(3), especially those derived from inorganic acids, as shown in the table below:
Inorganic Acid Polyatomic Anions Derived from Acid Acceptable Name (4) Formula Acceptable Name (5) Formula nitric acid HNO3 nitrate NO3- nitrous acid HNO2 nitrite NO2- carbonic acid H2CO3 hydrogencarbonate HCO3- carbonate CO32- sulfuric acid H2SO4 hydrogensulfate HSO4- sulfate SO42- sulfurous acid H2SO3 hydrogensulfite HSO3- sulfite SO32- phosphoric acid H3PO4 dihydrogenphosphate H2PO4- hydrogenphosphate HPO42- phosphate PO43- phosphorous acid H3PO3 dihydrogenphosphite H2PO3- hydrogenphosphite HPO32- phosphite PO33- perchloric acid HClO4 perchlorate ClO4- chloric acid HClO3 chlorate ClO3- chlorous acid HClO2 chlorite ClO2- hypochlorous acid HClO hypochlorite OCl-
Note that in the accepted abbreviated "hydrogen names"(6) of anions there is no space between the word "hydrogen" and the rest of the name:
hydrogencarbonate NOT hydrogen carbonate
- You may be expected to know the name and formula of this polyatomic anion derived from an inorganic base (7):
hydroxide : OH-