stock system name for CrO3 Is it Chromium (VI) trioxide or Chromium (VI) oxide?
The correct answer and explanation is :
The correct Stock system name for CrO₃ is Chromium (VI) oxide, not Chromium (VI) trioxide.
Explanation:
- Stock System Naming:
- In the Stock system, the oxidation state of the metal is written in Roman numerals within parentheses after the element name.
- Chromium can exhibit multiple oxidation states, but in CrO₃, it has an oxidation state of +6 (since oxygen is typically -2 and there are three oxygens, the total charge is -6, requiring chromium to be +6 for neutrality).
- Thus, the cation is Chromium (VI).
- Oxide vs. Trioxide:
- “Oxide” is the preferred term for compounds containing only metal and oxygen in systematic nomenclature.
- “Trioxide” is a molecular naming convention used primarily for covalent compounds, such as SO₃ (Sulfur trioxide) or N₂O₃ (Dinitrogen trioxide).
- Since CrO₃ is an ionic compound (a metal combined with oxygen), it follows the ionic nomenclature, making Chromium (VI) oxide the correct name.
- Comparison with Other Chromium Oxides:
- Cr₂O₃ is named Chromium (III) oxide.
- CrO₂ is named Chromium (IV) oxide.
- CrO₃ follows the same pattern, making Chromium (VI) oxide its correct name.
- Common Mistake:
- The term “trioxide” is sometimes mistakenly used because CrO₃ contains three oxygen atoms.
- However, systematic IUPAC naming for metal oxides does not use prefixes like “mono-“, “di-“, or “tri-” unless necessary for clarity (such as with non-metal oxides).
Thus, the correct Stock system name is Chromium (VI) oxide.