Chemistry / Unit 5: Chemical Names and Formulas
5.3 Naming Molecular Compounds
Notes
Molecular (covalent) compounds are made of two nonmetals. Use prefixes to show the number of each atom.
- Prefixes: 1 mono, 2 di, 3 tri, 4 tetra, 5 penta, 6 hexa, 7 hepta, 8 octa, 9 nona, 10 deca.
- Do not use "mono" on the first element: CO is carbon monoxide, not monocarbon monoxide.
- The second element ends in -ide. Drop a vowel before "oxide" when it doubles up: pentoxide, monoxide.
- Examples: $\text{N}_2\text{O}_4$ is dinitrogen tetroxide; $\text{SF}_6$ is sulfur hexafluoride; $\text{P}_4\text{O}_{10}$ is tetraphosphorus decoxide.
- Never use prefixes for ionic compounds.
Practice
What is the name of $\text{CCl}_4$?
Two nonmetals, so use prefixes; skip "mono" on the first element.
What is the formula of dinitrogen pentoxide?
di = 2 nitrogens, penta = 5 oxygens.
Which compound is named correctly?
Prefixes are used only for molecular compounds like $\text{SO}_3$. $\text{PCl}_3$ needs "trichloride."
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