CPR Assignment 2: Nomeclature
Naming Compounds

Before we attempt to name a compound we must first distinguish if a compound is ionic or molecular by identifying the types of elements that make up the compound.
Ionic compounds are made when a metal combines with a non-metal.
Molecular compounds are composed of a non-metal plus another non-metal.

Naming Ionic Compounds
  • The positively charged element (cation) is named first and retains it's name. (example: NaCl Sodium Chloride)
  • The negatively charged element (anion) is written last, but the end of it's name is replaced by -ide. (example: NaCl Sodium Chloride)
  • In compounds containing polyatomic ions, the cation is named first an anion last, and both retain their original names. (example: NaOH = sodiumhydroxide)
  • Cations followed by Roman numerals in parenthesis must be named using the Stock method. Roman numerals indicate that the metal (positive element) has more than one possible oxidation number and is a direct description of the metal's the oxidation. (example: Iron (II) Fluoride is pronounced Iron Two Flouride, and the Roman numeral tells us that the Iron in this case has an oxidation of 2+. Iron (III) Fluoride is pronounced Iron Three Flouride, and has an oxidation of 3+)
  • Multi-oxidated metals can also be named using the older common name method. This method uses the element name's old latin root and changes the ending to -ous for the lower charge, and -ic for the higher charge. (example: Iron (II) Flouride would now be called Ferrous Flouride, Iron (III) Flouride turns into Ferric Flouride)Some latin prefixes include : Iron (Ferr-), Lead (Plum-), Tin (Stann-), and Copper (Cupr-).


Naming Molecular Compounds
  • The element to the left of the periodic table is named first and remains unchanged.
  • The ending of the second element must be changed to -ide
  • Greek prefixes are used to determine the number of atoms of each element. Mono=1 (usually ommitted), di=2, tri=3, tetra=4, penta=5, hexa=6, hepta=7, octa=8, nona=9, deca=10. (example: CO2 carbon dioxide N2O5 dinitrogen pentoxide)

Nomeclature Examples
MgBr2 Magnesium Bromide
In this ionic compound Magnesium is positively charged, so it is written first. Bromide is named last because it is negatively charged. Notice that the original name of this element is Bromine, but we have changed the -ine to -ide, but Magnesium remains untouched.
CS2 Carbon Disulfide
In this molecular compound Carbon is named first because it can be found closer to the left on the periodic table. It's name remains, but it is possible to call it Monocarbon because there is only one atom of carbon. Since there are 2 Sulfur atoms, and because it comes last, we change the name to Disulfate.
Fe2O3 Iron(III) Oxide
Since this is an ionic compound Iron is first, as it is positively charged, and has the Roman numeral 3 because the Iron in this case has a charge of 3+. Oxygen is negatively charged and has been changed to Oxide.
FeO Iron(II) Oxide
Another ionic compound: Iron is written fist because it is a cation, and in this case the Roman numeral tells us that is has a charge of +2. Oxygen is once again changed to Oxide.
N2O5 Dinitrogen Pentoxide
Since Nitrogen is to the left of Oxygen, it is written first, and it's name is changed to Dinitrogen because there are 2 Nitrogen atoms in the compound. Because there are 5 oxygen atoms and because it is to the right of Nitrogen, we express Oxygen as Pentoxygen in this molecular compound
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