The system used for naming chemical substances depends on the nature of the molecular units making up the compound. These are usually either ions or molecules; different rules apply to each. In this section, we discuss the simplest binary (two-atom) molecules.
Numbers in names
It is often necessary to distinguish between compounds in which the same elements are present in different proportions; carbon monoxide CO and carbon dioxide CO2 are familiar to everyone. Chemists, perhaps hoping it will legitimize them as scholars, have long used Latin and Greek roots to designate numbers within names; you will encounter all but the grayed-out ones frequently, and you should know them.
Binary compounds of non-metalsThese two-element compounds are usually quite easy to name because most of them follow the systematic rule of adding the suffix -ide to the root name of the second element, which is normally the more "negative" one.
SiO2 silicon dioxidePBr3 phosphorus tribromide
N2O5 dinitrogen pentoxide
HCl hydrogen chloride
GaAs gallium arsenide
CCl4 carbon tetrachloride
As noted above, there are some important exceptions:
H2O (water, not dihydrogen oxide)
H2O2 (hydrogen peroxide, not dihydrogen dioxide)
H2S (hydrogen sulfide, not dihydrogen sulfide)
NH3 (ammonia, not nitrogen trihydride)
NO (nitric oxide, not nitrogen monoxide)
N2O (nitrous oxide, not dinitrogen oxide)
CH4 (methane, not carbon tetrahydride)
