HELP explain when the “mono-prefix is and is not used when naming molecular compounds. Include the name of the compound CO as part of your explanation.
The Correct Answer and Explanation is :
In naming molecular compounds, the “mono-” prefix is used to indicate the presence of a single atom of an element. However, its use follows certain rules of convention:
When “mono-” is not used:
- First Element: If there is only one atom of the first element in the compound, the “mono-” prefix is typically omitted. For example, in the compound CO (carbon monoxide), there is one atom of carbon and one atom of oxygen. Since carbon is the first element, “mono-” is not used for it. The compound is named carbon monoxide instead of “monocarbon monoxide.”
- Simple Covalent Compounds: In some cases, particularly in well-known simple covalent compounds, “mono-” is not used for historical reasons. For example, nitrogen dioxide (NO₂) does not use “mono-” for nitrogen, even though there’s one nitrogen atom.
When “mono-” is used:
- Second Element: When the second element in a compound has only one atom, the “mono-” prefix is used. In CO, the second element is oxygen, which has one atom, so “mono-” is added to form “monoxide,” meaning one oxygen atom.
- Clarifying the Number of Atoms: When the second element has multiple possibilities in its number of atoms (as in CO and CO₂), the prefixes ensure clarity. In CO₂, for example, “di-” is used to show there are two oxygen atoms, naming it carbon dioxide.
Summary with Example (CO):
- CO is named carbon monoxide. The “mono-” is not used for carbon because it is the first element, but it is used for oxygen to indicate there is one oxygen atom. This systematic approach prevents ambiguity and follows the rules of IUPAC nomenclature for binary molecular compounds.