A Headache
• FeCl2 would be called iron chloride.
• FeCl3 would be called …...
• ??????
Binary Compounds
(A Headache)
• FeCl2 would be called iron chloride.
• FeCl3 would be called iron chloride.
• BUT .... two different substances cannot
have the same name.
• Since iron has two possible valences
(multiple valences) the name must reflect
which valence is being used.
One Solution
• FeCl2 is called iron(II) chloride
• FeCl3 is called iron(III) chloride
This method of naming compounds is
called the Roman Numeral (or Stock or
IUPAC) system.
• NOTE: The Roman numeral refers to the
valence of the first element.
Roman Numeral System
•
•
•
•
•
•
PbI2
lead(II) iodide
CO
carbon(II) oxide
CO2
carbon(IV) oxide
FeBr2 iron(II) bromide
UCl4
uranium(IV) chloride
MgCl2 magnesium chloride
(no multiple valences involved here.)
Another Solution
You can also use the Prefix System - adding
a prefix to the name of the last element
indicating how many atoms of that element
appear in the formula:
• CO
carbon monoxide
• CO2
carbon dioxide
• Note: “mono” and “penta” used with oxide
are contracted to monoxide and pentoxide.
Examples - Prefix System
•
•
•
•
•
SO3
SnO2
UO3
P2O5
N 2O 3
sulphur trioxide
tin dioxide
uranium trioxide
phosphorus pentoxide
dinitrogen trioxide
(nitrogen compounds sometimes
use two prefixes)
Writing Formulae
involving Multiple Valences
The Roman numeral gives the valence to
use for the first element; the second
element will never have more than one
possible valence - taken from the negative
oxidation number. Apply the cross-over
technique:
• lead(IV) chloride
• tin(II) oxide
PbCl4
SnO
Writing Formulae
involving Multiple Valences
The prefix system tells you the number of
atoms represented in the final formula.
Use the possible valences of the first
element and the valence of the second to
determine the formula that matches the
information given by the prefix in the
name:
• carbon disulphide
• phosphorus trioxide
CS2
P2O3
Practice Time !!!
Now you can work on the second
nomenclature practice page.