if technetium is manmade then how did Mendeleev left gaps for it?
Answers
Explanation:
Technetium long tantalised chemists because it could not be found. We now know that all its isotopes are radioactive and any mineral deposits of the element had long disappeared from the Earth’s crust. (The longest lived isotope has a half life of 4 million years.) Even so, some technetium atoms are produced as uranium undergoes nuclear fission and there is about 1 milligram of technetium in a tonne of uranium. Claims in the 1920s to have found this element, or at least to have observed its spectrum, cannot be entirely discounted.
Technetium was discovered by Emilio Segrè in 1937 in Italy. He investigated molybdenum from California which had been exposed to high energy radiation and he found technetium to be present and separated it. Today, this element is extracted from spent nuclear fuel rods in tonne quantities.
MENDELEEV HAD LEFT GAPS FOR FUTURE ELEMENT PREDICTIONS