Final answer:
Greek prefixes are used when naming molecular compounds to indicate the number of atoms; this is not the case for naming ionic compounds, transition metals, or polyatomic ions, except when the ion name inherently includes a prefix.
Step-by-step explanation:
Greek prefixes are used when naming molecular compounds. These prefixes indicate the number of each type of atom present in the compound. Examples of such prefixes include mono-, di-, tri-, tetra-, etc. When naming simple binary molecular compounds, the less electronegative element is named first, and then the second element's name is followed by the '-ide' suffix, incorporating the appropriate numerical prefix to specify atom count.
When naming ionic compounds, the Greek prefixes are not used; instead, the name begins with the metal (the cation) followed by the nonmetal (the anion), changing its ending to '-ide'. With transition metals that can have multiple oxidation states, the specific charge of the metal ion is indicated in the compound's name using Roman numerals. For example, FeCl2 is iron(II) chloride, not using prefixes.
Polyatomic ions follow similar naming rules to other ionic compounds without the use of prefixes. However, some polyatomic ions themselves contain numerical prefixes as part of their name, such as the sulfate (SO4^2-) and phosphate (PO4^3-) ions.