thallous

Thallous is a technical adjective used in chemistry for compounds or ions containing thallium in the +1 oxidation state. The term distinguishes this lower oxidation state from thallic, which denotes thallium in the +3 state. A thallous ion is therefore written Tl⁺, while its compounds are often described more explicitly as thallium(I) compounds. The word appears chiefly in inorganic chemistry, chemical nomenclature, and discussions of coordination or crystal chemistry. In broader scientific and historical writing, it is associated especially with the toxic effects of soluble thallium(I) compounds. Although the distinction is chemically meaningful, modern technical literature often uses the more explicit “thallium(I)” notation. Thallous remains useful when readers need a direct adjective that identifies the oxidation state of thallium and contrasts with “thallic.”

Of or relating to thallium in the +1 oxidation state; containing thallium as the thallium(I) ion.

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Where does thallous come from?

Thallous was formed in English chemical terminology from the element name thallium and the suffix “-ous.” The element name thallium comes from Greek thallos, meaning “green shoot,” a reference to the green line in thallium's spectrum. In chemical usage, thallous became established alongside thallic to distinguish thallium's +1 and +3 oxidation states.

How thallous is actually used

This is specialized, formal terminology used primarily in inorganic chemistry. It is not interchangeable with “thallium” in general prose because it specifies an oxidation state rather than merely naming the element.

Easily confused with thallous

Words and phrases paired with thallous

What's the opposite of thallous?

Rhymes with thallous