What is Promethium atom?

     

Promethium is a chemical element with the symbol Pm and atomic number 61.  All of its isotopes are radioactive; it is extremely rare, with only about 500-600 grams naturally occurring in Earth's crust at any given time.  Promethium is one of only two radioactive elements that are followed in the periodic table by elements with stable forms, the other being lanthanide.  Promethium shows only one stable oxidation state of +3.

     In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium(60) and samarium (62);  this was confirmed in 1914 by Henry Moseley, who, having measured the atomic numbers of all the elements then known, found that atomic number 61 was missing.

     In 1926, two groups claimed to have isolated a sample of elements 61;  both "disciveries" were sooon proven to be false.  In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not generally recognized.