What does cobaltous mean?
Cobaltous is a technical adjective used in chemistry to identify a compound or ion containing cobalt in the +2 oxidation state. It is equivalent in meaning to “cobalt(II)” and describes cobalt as divalent, with each cobalt atom formally associated with a two-positive charge. Familiar examples include cobaltous chloride, cobaltous oxide, and cobaltous sulfate. The word is especially useful because different compounds can contain the same element while giving that element different oxidation states and properties. Cobaltous must therefore be distinguished from cobaltic, which denotes cobalt in the +3 state, and from the unqualified word cobalt, which names the element without specifying its chemical combination. In modern technical writing, cobalt(II) is often clearer and more explicit than cobaltous, but the older adjective remains established in chemical nomenclature. The word belongs primarily to formal scientific and industrial contexts rather than everyday speech.
adjectiveDenoting a compound or ion in which cobalt has the +2 oxidation state, also called divalent cobalt.
- Relating to or containing cobalt in the +2 oxidation state.
"The electrolyte contained a cobaltous salt, providing a steady supply of Co²⁺ ions."
"Cobaltous chloride is used as a starting material for preparing other cobalt compounds."
"The analyst tested the solution for cobaltous ions."
Cobaltous is chemistry’s precise way of saying “cobalt with a +2 charge”—and the ending “-ous” is not its name.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does cobaltous come from?
Cobaltous was formed from cobalt with the adjectival suffix -ous and was developed in chemical usage to distinguish divalent cobalt from cobaltic compounds. Cobalt entered English from German Kobalt, a miners’ term associated with Kobold, meaning “goblin,” in reference to troublesome ores that yielded undesirable arsenic compounds. Kobold and the related word goblin also reflect this historical tradition.
How cobaltous is actually used
This is a formal, specialized chemical term, typically used attributively in the names of compounds. It should not be used as a general synonym for “cobalt-containing,” because several cobalt compounds have cobalt in other oxidation states.
Easily confused with cobaltous
Cobalt alone names the chemical element, whereas cobaltous specifically denotes cobalt in the +2 oxidation state.
Cobaltous denotes cobalt with an oxidation state of +2, while cobaltic denotes cobalt with an oxidation state of +3.