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Four isotopes of astatine were subsequently found to be naturally occurring, although much less than one gram is present at any given time in the Earth's crust. Neither the most stable isotope, astatine-210, nor the medically useful astatine-211 occur naturally; they are usually produced by bombarding bismuth -209 with alpha particles .
World Book Encyclopedia, Exploring Earth. HyperPhysics, Georgia State University, Abundance of Elements in Earth's Crust. Eric Scerri, The Periodic Table, Its Story and Its Significance, Oxford University Press, 2007 "EarthRef.org Digital Archive (ERDA) -- Major Element Composition of the Core vs the Bulk Earth". earthref.org
The abundance of the chemical elements is a measure of the occurrences of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction (in commercial contexts often called weight fraction), by mole fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases), or by volume fraction.
Neodymium is a fairly common element in the Earth's crust for being a rare-earth metal. Most rare-earth metals are less abundant. Neodymium is classified as a lithophile under the Goldschmidt classification, meaning that it is generally found combined with oxygen. Although it belongs to the rare-earth metals, neodymium is not rare at all.
Lanthanum is the strongest and hardest base among the rare earth elements, which is again expected from its being the largest of them. [34] Some lanthanum(II) compounds are also known, but they are much less stable. [17] Therefore, in officially naming compounds of lanthanum its oxidation number always is to be mentioned.
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A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...