Naming Ionic Compounds
Changing Chemical Formula into Compound Name:
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use these two rules:
o 1st element (the metal) – write down the elements full name
o 2nd element (the non metal) - start with the elements name, then change the ending
with “ide”
** this is just like you learned for molecular compounds
except you are not worried about the numbers of an element
examples:
NaCl – sodium chloride
CaCl2 – calcium chloride
Mg3N2 – magnesium nitride
PbO – lead oxide
Changing Compound Name into Chemical Formula:
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this is harder because you must balance out the electronic charges to zero!
use these rules:
o write down the symbols for the elements in the order they appear in the compound
name – the metal will always be first and the non metal second
e.g. calcium chloride…. write down CaCl
o figure out the ionic charge of each element from the periodic table – normally metals
have a positive charge and non metals have a negative charge
e.g. Ca has a +2charge and Cl has a -1charge
o add a number to the elements so that the total charge of the compound equals zero
e.g. one atom of Ca with a total charge of +2 needs two atoms of Cl to give a 2 charge (2 x -1) so the balance of +2 and -2 is zero → so its CaCl2
examples:
potassium iodide – KI
barium chloride – BaCl2
aluminium sulphide – Al2O3
sodium sulfide – Na2S
BUT some elements have more than one ion charge → e.g. Fe, Cu, Pb
in order to show clearly which ion is being used in the chemical formula a Roman numeral is
added in brackets behind the metal e.g. iron (II) oxide or FeO is a compound containing Fe2+
and O2- and iron (III) oxide or Fe2O3 is a compound containing Fe3+ and O2-