Chemical Nomenclature: Part II
The nomenclature work that you have done so far is all that is needed if only one binary
compound of the two elements exists. Many combinations of two elements, however, can result in
more than one compound. For example, iron and chlorine react to produce both FeCl2 and FeCl3,
which have demonstrably different properties, and so the name iron chloride is ambiguous.
Whenever two or more compounds of the same two elements are possible, one of two approaches
to modifying the name is used. Both approaches are valid, although one may be more appropriate
with a particular compound than the other. Very few compounds are named using both
approaches.
Oxidation States and the Stock System
The first of these approaches taken when two or more different compounds of the same elements
exist is the oxidation state approach, also called the Stock system (after the chemist A.T. Stock). It
can be rationalized in the following simple discussion, which is a brief summary of a more
elaborate discussion we will take up later.
The oxidation state of an element in a compound is denoted by placing a Roman numeral after the
name of the element. Oxidation states are given if and only if they are necessary to make the
name unambiguous.
Example. In the case of sodium chloride, oxidation states are unnecessary because only one
binary compound of these two elements is known to be +1. It is always +1 and nothing else. In
the case of iron chloride, oxidation states should be used. For FeCl2, the correct name is iron (II)
chloride, and, for FeCl3, the correct name is iron (III) chloride. The oxidation state of elemental
iron is iron(0); that of Fe2+ is iron (II); and that of Fe3+ is iron (III). The iron in FeCl2 or FeO is
also iron (II), while that in FeCl3 or Fe2O3 is iron (III).
Calculation of the oxidation state of an element when it is combined in a compound or ion has
many different approaches. It usually depends on who is teaching it and how they first learned it
themselves from their teachers. It can be done by the application of one definition and a few
general properties of some of the common elements. The definition is as follows:
The sum of the oxidation states of all the elements in a compound is zero; the sum of the
oxidation states in an ion (positively or negatively-charged species) is equal to the net charge on
the ion.
The properties of the elements used to determine oxidation state are, in order of precedence:
♦ The oxidation state of the alkali metals (Group 1) in compounds is normally 1+
and the oxidation state of the alkaline earths (Group 2) is normally 2+. (There
are virtually no exceptions.)
♦ The oxidation state of oxygen in compounds is normally 2-. (The only
significant exceptions are the peroxides, such as H2O2 and Na2O2, in which the
oxygen is in the 1- oxidation state.)
♦ The oxidation state of hydrogen in compounds is normally 1+. (The only
significant exceptions are the saline hydrides, such as LiH, in which hydrogen
is in the 1- oxidation state.)
1
♦ The oxidation state of the halogens in compounds is normally 1-. (The only
significant exceptions are those compounds of the halogens which also include
oxygen, such as NaClO4.)
♦ The oxidation state of most other elements in chemical compounds can vary,
and is obtained by difference using the definition and the general properties of
these common elements. Most of the transition metals have several different
oxidation states.
♦ Transition elements that have only one valence such as Ag1+, Sc3+, Y3+, Zr4+,
Tc7+, or Cd2+ do not need brackets indicating their charge. Putting them in is
not incorrect but it would be a chemical social faux paus.
Example. To name the compound NiO2, first name the elements: nickel oxygen. Second, change
the ending: nickel oxide. Third, calculate the oxidation state of nickel: 0 (compound) = x + 2 (2-);
0 = x - 4;x = 4+. This gives the name: nickel (IV) oxide. The oxidation state of oxygen need not
be specified.
Example. To name the compound V2O5, first name the elements: vanadium oxygen. Second,
change the ending: vanadium oxide. Third, calculate the oxidation state of vanadium:
0 = 2x + 5 (2-); 0 = 2x - 10; 10 = 2x; x = 5+.
This gives the name: vanadium (V) oxide.
There is an older nomenclature for compounds with variable oxidation state traceable to
Lavoisier, in which the higher oxidation state of an element is designated by an -ic ending on the
element name and the lower by an -ous ending, as vanadous oxide (VO) and vanadic oxide
(V2O3). Since this system fails when more than two oxidation states are known for the same
element, and the numeric oxidation state designated by -ic or -ous endings changes from element
to element, it is obsolete. Modern chemists no longer use it for binary compounds, although traces
of it still remain in the nomenclature of less simple compounds. Some commercial manufacturers,
however, still label their products in the old way.
The older method was made up based on the few metals that were known in the past. The name
also is derived from the old name of the elements.
Element
Fe
Cu
Sn
Au
Hg
Pb
Sb
New Name
Iron
Copper
Tin
Gold
Mercury
Lead
Antimony
Old Name
Ferrum
Cuprum
Stannum
Aurum
Hydroargentum
Plumbum
Stibbum
2
Possible valences
2+, 3+
1+, 2+
2+, 4+
1+, 3+
1+, 2+
2+, 4+
3+, 5+
The "ous"-"ic" System
As you can see above these metals only had two possible valences. A system that distinguishes
between only two is fine and that is what the "ous"-"ic" system did.
The lower valence metal had its named changed to end in "ous" while the higher valence metal
had its names changed to end in "ic".
Example:
Fe2+
Cu1+
Sn2+
Au1+
Pb2+
Sb3+
Hg1+
ferrous
cuprous
stannous
aurous
plumbous
stibbous
mercurous
Fe3+
Cu2+
Sn4+
Au3+
Pb4+
Sb5+
Hg2+
ferric
cupric
stannic
auric*
plumbic
stibbic
mercuric**
* Chemistry trivia time: In the James Bond movie Goldfinger who was the villian? Auric
Goldfinger
What was the license plate number on Goldfinger's Rolls Royce?
What was the name of Goldfinger's business establishment?
Enterprises
AU3
Auric
** Mercury's name was changed because hydroargentous and hydroargentic would be just to
much to handle.
This system work's quite well with elements possessing 2 possible valences. The problem lies in
the fact that a few elements have more than two valences. Vanadium has 4 possible valences
(5+, 4+, 3+, and 2+) and manganese has 5 (7+, 6+, 4+, 3+, and 2+). Using the "ous"-"ic" system
we could only name the first two lowest valences. It is for this reason that the Stock system is in
prominent use today.
Stop here and do Nomenclature Exercise #5
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Counting in Greek
This approach is used when naming compounds that are made up of non-metal elements only. The
numeric or numbering approach is used when the oxidation state approach either does not
unambiguously name the compound . We can't use it with non-metal to non-metal compounds.
Example: NO2 and N2O4, both of which exist, could both be named nitrogen(IV) oxide.
In either case, the alternative naming approach is to give the numbers of atoms of each element in
the molecule, using Greek prefixes.
The first ten Greek prefixes are:
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca
The prefix nona is Latin rather than Greek. The Greek prefix, used only in very specialized
chemical nomenclature, would be ennea.
Example. The compound CO is carbon mono oxide, or carbon monoxide; CO2 is carbon di oxide,
or carbon dioxide; and SO3 is sulfur tri oxide, or sulfur trioxide.
Stop here and do Nomenclature Exercise #6
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Nomenclature Exercise #5 - Creating Formulas for the Transition Metals
Using the IUPAC formulas below come up with correct names
1.
ScCl3
16.
PtO2
2.
Cr(NO3)6
17.
Zn3P2
3.
MnO
18.
Sn(HSO4)4
4.
Fe(MnO4)2
19.
Au2O3
5.
CoF3
20.
Bi3(BO3)5
6.
Ni3(PO4)2
21.
NiN
7.
CuCl2
22.
TiO2
8.
ZnO
23.
VSO4
9.
GeS2
24.
Cr(H2PO4)3
10.
AgCl
25.
W(MnO4)4
11.
Cd3N2
26.
UO2
12.
SnF2
27.
Pu2O5
13.
Sb(ClO3)5
28.
Fe(HCO3)3
14.
Pb(SO4)2
29.
Al2O3
15.
HgI
30.
CuBr
5
Given the names below provide the correct IUPAC formulas.
1.
Chromous chloride
16. Chromium (II) sulphate
2.
Ferric nitrate
17. Manganese (IV) phosphide
3.
Plumbic hydroxide
18. Iron (III) sulphide
4.
Cobaltous bisulphate
19. Cobalt (II) dichromate
5.
Nickelic borate
20. Nickel (III) nitride
6.
Cuprous sulphate
21. Copper (I) cyanide
7.
Cupric monohydrogen phosphate
22.
Zinc carbonate
8.
Mercurous bromide
23.
Cadmium phosphate
9.
Bismuthic carbonate
24.
Mercury (II) iodide
10. Stannous bicarbonate
25.
Gold (III) permangante
11. Mercuric oxide
26.
Platinum (II) acetate
12. Plumbous chloride
27.
Vanadium (V) chromate
13.
28.
Aluminum biphosphate
14. Plumbic nitrate
29.
Uranium (V) nitrate
15. Stannic bisulphate
30.
Silver hydroxide
Bismuthous fluoride
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Nomenclature Exercise #6 - Creating Formulas for Non-metal to Non-metal Compounds
Using the names below come up with the correct formulas.
1.
Carbon dioxide
8. Dinitrogen tetraoxide
2.
Bromine monoxide
9. Chlorine trifluoride
3. Iodine monochloride
10.
Phosphorus pentachloride
4. Antimony trifluoride
11.
Bromine monofluoride
5. Bromine dioxide
12.
Dinitrogen pentoxide
6. Carbon monosulphide
13.
Carbon tetraiodide
7. Phosphorus tribromide
14.
Tellurium dioxide
Given the formulas below provide the correct names.
1. SiC
8. CS2
2. SiO2
9. CO
3. SbBr3
10. BrF5
4. IBr
11. SbCl3
5. SiCl4
12. IF5
6.
N2O
13. SO2
7.
CSe2
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