Elements above Uranium don't exist in nature b/c they have short half-lifes but elements below Uranium do.How?

Question

Elements above uranium in the periodic table do not exist in nature b/c they have short half-lives. There are many elements below Uranium that have equally short half-lives, but do exist in appriciable amounts in nature. How can you accont for this?

Answer 1

Not entirely true. Plutonium (atomic # 93) has a very long 1/2 life. Technetium (# 43) isn't found in nature. Many trans Uranium elements do have short 1/2 lives however. The simple explanation is that nucleii just get too big to be stable.

Answer 2

The isotopes with short half-lives that you are thinking of are produced by the decay of longer-lived isotopes. Since there is a small amount being produced all the time, the short half-life isn't as relevant. There is a equilibrium between the production from the long half-life isotope and the decay of the short half-life isotope. For the elements past Uranium, there are no sufficiently long lived, even larger, isotopes to produce them.

It should also be pointed out that some isotopes of Plutonium are rather long lived, but not on a geologic time scale. A half life of hundreds of thousands of years is not long when talking about billions of years.

Answer 3

those elements would ahve existed at the time of the Suns formation; however due to that being 5 million years ago they have almost all decomposed into lower atomic mass elements, such as Uranium, Lead and others. Uranium is still around at its half life is 710 million years, so a fairly substancial amount is still around. interesting - well to me anyway - almost all the lead on earth was once Uranium or other radioactive substances.

Answer 4

Isotopes. Some of them are unstable (example, carbon-14) but most of them are stable. There are two artifical elements, Technetium (At. # 43) and Promethium (At. # 61) with very short half lives, and they don't exist (very long) in nature.