actinium

noun

ac·​tin·​i·​um ak-ˈti-nē-əm How to pronounce actinium (audio)
: a radioactive trivalent metallic element that resembles lanthanum in chemical properties and that is found especially in pitchblende see Chemical Elements Table

Examples of actinium in a Sentence

Recent Examples on the Web
These examples are automatically compiled from online sources to illustrate current usage. Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
Since 2015 a working group at the International Union of Pure and Applied Chemistry has been refereeing a debate over which elements should go in the third column of the table: lanthanum and actinium (elements 57 and 89) or lutetium and lawrencium (71 and 103). Stephanie Pappas, Scientific American, 14 May 2024 Those protons smashing and staying put creates the right kind of actinium through a process called spallation. Sarah Scoles, Scientific American, 13 Feb. 2024 For years, scientists have produced this species of actinium by waiting for thorium (element 90, with one extra proton than actinium) to decay. Sarah Scoles, Scientific American, 13 Feb. 2024 The lanthanide and actinide series — those two rows floating by themselves, named after their first members, lanthanum and actinium — are isolated like that as a concession to limited space. Bill Andrews, Discover Magazine, 26 June 2019 Other theorists have predicted that hydrides such as calcium hydride or actinium hydride should superconduct at close to room temperature—and at a pressure considerably less than that needed for CSH. Robert F. Service, Science | AAAS, 26 Aug. 2021

Word History

Etymology

borrowed from French, from Greek aktīn-, aktís "ray, beam" + -ium -ium; so called from its radioactivity — more at actin-

First Known Use

1900, in the meaning defined above

Time Traveler
The first known use of actinium was in 1900

Dictionary Entries Near actinium

Cite this Entry

“Actinium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/actinium. Accessed 7 Nov. 2024.

Kids Definition

actinium

noun
ac·​tin·​i·​um ak-ˈtin-ē-əm How to pronounce actinium (audio)
: a radioactive metallic element found especially in pitchblende see element

Medical Definition

actinium

noun
ac·​tin·​i·​um ak-ˈtin-ē-əm How to pronounce actinium (audio)
: a radioactive trivalent metallic element that resembles lanthanum in chemical properties and that is found especially in pitchblende
symbol Ac
see Chemical Elements Table

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