Naming Binary Molecular Compounds

Binary molecular compounds are compounds that consist of exactly two nonmetal elements. Examples include HF, NO2, and P2O5. Naming binary molecular compounds is really quite easy. The first element is given its element name; the second is given its root (hydr, bor, carb, ox, fluor, etc.) followed by ide.

For example, HCl is hydrogen chloride, and H2Se is hydrogen selenide.

Greek Prefixes Specify the Number of Atoms of Each Element

To be unambiguous (N2O, NO, NO2, and N2O4 all exist), we use Greek prefixes to explicitly indicate how many of each element are present. You need to memorize at least the first six Greek prefixes:

1=mono 2=di 3=tri 4=tetra 5=penta 6=hexa

Beyond that, it's simply a matter of remembering the following four rules to make the names a little more readable:

• Rule 1: Drop mono for the first element

• Rule 2: Drop all prefixes if the first element is H

• Rule 3: Drop the second o in mono prior to a vowel

• Rule 4: Drop the a in prefixes ending in a prior to a vowel

Examples include:

N2S dinitrogen monosulfide(standard)

N2O3 dinitrogen trioxide(standard)

CO2 carbon dioxide - Rule 1

HCl hydrogen chloride - Rule 2

CO carbon monoxide - Rule 3

N2O4 dinitrogen tetroxide - Rule 4

Summary

In summary, memorize the 15 nonmetal element names and symbols, memorize the first 6 prefixes, learn the four rules, and practice.

YOU CAN DO IT!