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Asked by 245drud47 to Anne, Florence, Mark, Neil, Sinead on 6 Nov 2015.
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Sinead Balgobin answered on 6 Nov 2015:
The rarest elements are the ones that are made in a lab- they don’t exist naturally on earth so when scientists make them, that’s all there is! They are also usually quite unstable, so they don’t last for very long before they turn into something else. Element 115 (which doesn’t have a proper name, only Ununpentium) has only been made about twice, and because it is so unstable it breaks down almost immediately so only 50 atoms have ever been measured. Which is so tiny I can’t even imagine how little that would weigh.
That’s a sort of cheat answer though, because I guess you are really asking what are the rarest ones you can already find on Earth? In that case I think Astatine and Francium hold that record. They are both very rare too, and were only discovered after being made in a lab, but they do exist naturally on Earth. Astatine is made for a very short time when Uranium breaks down (e.g. in a nuclear reactor). Francium is also made by the break down of another element, actinium, and scientists think that there is probably only ever 30 grams of it on the earth at any one time.
The rarest stable metal is Tantalum- apparently there are over 181 billion atoms of OTHER elements for every ONE atom of tantalum in the universe. It doesn’t break down quickly like astatine and francium.
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Mark Collins answered on 6 Nov 2015:
The hardest elements to find are those we create! A town in Germany Darmstadt they have a huge collider and they can collide and fuse large numbers of nuclei to create a new element, based on the great work already performed by other scientists we can predict what this element will be like and how it will be behave even if it only exists for a fraction of a second! This is great thing about science, the work we do is not only for us but it can be used generations from now! And to go back to the new element as we know what we are expecting, it can be easier to find it! There are other elements that are hard to find, some that are just plain rare like Tantalum and others that create really strong bonds with oxygen and other elements so they can remain hidden for many hundreds of years as we look for them. It is only through some great Chemistry and a lot of persistence we can separate these from their oxygen and see the element in its purest form! The next time you see some rocks, there may be rare elements bound within the rock! It is very exciting, chemistry is all around us at all times…we just need to find it.
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