Chemical Nomenclature 2
Multivalent Elements (elements with more than 1 valence)
Many elements in the periodic table can bond using electrons from lower levels to become stable. For example, iron
can have a 2+ or 3+ oxidation number, so you can have FeCl2 or FeCl3. Writing chemical formulas would be the same as
other binary compounds once you know which oxidation number to use, but obviously iron chloride is not good enough for a
name as it does not specify a specific formula and we must distinguish these two compounds since they have distinctly different
chemical properties. If an element has more than one possible oxidation number, it is indicated on the periodic table and the
most common oxidation number is in bold. Several different methods can be used to distinguish multivalent elements:
1. The Stock System (named after Alfred Stock and is most preferred and can be used for all multivalent elements)
Rules for Naming Compounds Using the Stock System For Multivalent Elements
1. Write the name of first element as before.
2. Write the valence of multivalent element as a capitalized roman numeral in brackets right after name leaving no space.
3. Write the name of other element with "ide" ending as before.
e.g.
FeCl2 is iron(II) chloride as iron has a 2+ valence
FeCl3 is iron(III) chloride as iron has a 3+ valence
2. The "Ous-Ic" System (only be used for certain metal multivalent elements that have historical industrial value)
This system relies on the Latin name of the multivalent element, but the ending of the Latin name is changed to ous for
the lower oxidation number and ic for the higher oxidation number. Here are the Latin names and valences you have to know.
English Name
Latin Name
Valances
iron
ferrum
2,3
copper
cuprum
1,2
lead
plumbum
2,4
tin
stannum
2,4
mercury
mercurum
1,2
e.g.
FeCl2 is ferrous chloride as iron has a 2+ valence
FeCl3 is ferric chloride as iron has a 3+ valence
3. The Prefix System (can only be used for non-metal multivalent elements)
Rules for Naming Molecules Using the Prefix System For Multivalent Elements
1. Add the appropriate prefix to name of either the first, second or both elements to indicate the number of atoms of that
element present in compound.
2. Write the name of second element with "ide" ending.
Number
Prefix
Number
Prefix
1
mono
5
penta
2
di
6
hexa
3
tri
7
hepta
4
tetra
8
octa
e.g.
CO carbon monoxide
CO2 carbon dioxide
e.g.2.
N2O4 dinitrogen tetroxide
Note that mono is never used for the first element and if the second element is oxygen and prefix for oxygen ends in
"a" or "o", the "o" or "a" is dropped. Also, notice that you don’t reduce the formula in this case because the non-metals bonded
to non-metals create molecules which are distinct particles so you must express this correctly as it represents the exact number
of atoms present. Ionic bonds can be reduced because the result is a crystal that just keeps growing so we can only express the
ratio of atoms. Finally, note that only the first element is used to determine if a special name is used; that is, our system is
based on the classification of the first element even if the second element is multivalent. Our system could have relied on the
second element, but the first element was chosen and we can flip-flop between methods or this becomes confusing. The second
element’s oxidation number is just determined using its family number as before.
Prepared by K. Zuber