Naming Binary Molecular Compounds

Binary molecular compounds are composed of only two elements. Examples are H2O, NO, SF6 etc. . Naming these binary compounds is a little bit more involved than naming salts. Why is this so? Molecular compounds are more difficult to name because the atoms combine through covalent and not ionic bonds. Therefore we cannot use the electrical neutrality rule for these compounds. Most molecular compounds are made from nonmetals.

Sometimes these compounds have generic or common names (e.g., H2O is "water") and they also have systematic names (e.g., H2O, dihydrogen monoxide). The common name must be memorized. The systematic name is more complicated but it has the advantage that the formula of the compound can be deduced from the name.

Simple binary compounds consist of only a few atoms. Systematic naming of these compounds follow the rules:

  • The elements , except for H, are are written in order of increasing group number (e.g., NO not ON)
  • The number of atoms of a given type is designated by a prefix such as di- , tri-, tetra- etc. (The exception to this rule is for the first atom: if the first atom is "mono" then no prefix for it is given.) (e.g., NO is nitrogen monoxide not mononitrogen monoxide)

 Compound  Systematic name
 Common name
(if it has one)
 NF3 nitrogen trifluoride   
 NO  nitrogen monoxide  nitric oxide
 NO2  nitrogen dioxide  
 N2O  dinitrogen monoxide  laughing gas
 N2O4  dinitrogen tetraoxide  
 PCl5  phosphorous pentachloride  
 SF6  sulfur hexafluoride  
 S2F10  disulfur decafluoride  
 H2O  dihydrogen monoxide water 
 H2S  dihydrogen monosulfide  hydrogen sulfide
 NH3  nitrogen trihydride  ammonia
 N2H4  dinitrogen tetrahydride  hydrazine
 PH3  phosphorous trihydride  phosphine

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C101 Class Notes
Prof. N. De Leon