Overview
This lecture covers the systematic naming of binary molecular compounds (molecules made of two nonmetal elements) using IUPAC conventions, focusing on the correct use of prefixes and naming order.
Binary Molecular Compound Naming Rules
- Binary molecular compounds contain exactly two different nonmetal elements.
- Naming follows IUPAC (International Union of Pure and Applied Chemistry) rules for consistency.
- Only elements to the right of the periodic table "staircase" (nonmetals) are considered.
- The typical naming template includes: [prefix] [name of first element] [prefix] [base of second element + "-ide"].
- Do not use the "mono-" prefix for the first element if only one atom is present.
- Always use a prefix for the second element, including "mono-" if only one atom is present.
- Combine vowels in prefixes (e.g., "mono" + "oxide" becomes "monoxide") to avoid double vowels.
- The order of elements is typically the more electropositive (leftmost) element first.
Naming Examples
- CO: Carbon monoxide (not monocarbon monoxide).
- CO₂: Carbon dioxide (not dicarbon dioxide).
- OCl₂: Oxygen dichloride.
- NO: Nitrogen monoxide.
- NO₂: Nitrogen dioxide.
- N₂O: Dinitrogen monoxide (also called nitrous oxide).
- N₂O₅: Dinitrogen pentoxide (accept "pentaoxide" but usually simplified to "pentoxide").
Writing Formulas from Names
- Sulfur hexafluoride: SF₆.
- Boron trihydride: BH₃.
- Tetraphosphorus decoxide: P₄O₁₀.
Common Naming Mistakes & Corrections
- H₂S is commonly called hydrogen sulfide, but IUPAC name is dihydrogen monosulfide.
- "Monooxygen monochloride" should be "oxygen monochloride"; omit "mono-" for the first element.
Key Terms & Definitions
- Binary molecular compound — a compound with exactly two different nonmetal elements.
- IUPAC — international body standardizing chemical nomenclature.
- Prefix — denotes the number of atoms (e.g., mono-, di-, tri-, tetra-, penta-).
- Electropositive — a measure of an atom's ability to give up electrons; more electropositive elements are named first.
Action Items / Next Steps
- Practice naming and writing formulas for binary molecular compounds.
- Prepare for next lecture on naming ionic compounds (metal cations and nonmetal anions).