Besides Technetium and Promethium, my periodic table says everything before Uranium (Atomic #92) is found in nature (on earth). Everything after isn’t. I figured since Promethium is in the Lanthanoid series, it isn’t unusual that it isn’t in nature (since most of them are rare). But Technetium is between Molybdenum and Ruthenium, which are a lot more common.
So is there a reason there isn’t any (with few exceptions dealing with radiation) on earth?
And the atomic number probably has very little to do with it’s rarity I know, but my point is that there are only two exceptions and I’d like to know why there are.
Promethium also has no stable isotopes. At #43 and #61, these elements are moderately unusual in having such low atomic numbers with no stable isotopes. A few more elements below 92, such as Astatine and Francium are present in such minute quantities as to effectively not exist - they have very short half lives and small amounts are presumably present as decay products in radioactive ores at any given time, but it would be far to much trouble to attempt to measure or isolate them. Webelements.com estimates the quantity of either of these elements in the Earth’s crust at any point as < 30 grams.
Technetium is the first element to have been artificially produced, hence the name.
As you can see, with the exception of Promethium, the ‘rare earths’ are more common than gold, platinum, tungsten, silver, tin (!), lead (!!) and a whole host of others. (though they are many magnitudes rarer than iron, nickel, etc)
Which is pretty much why we’ve stopped calling them that and changed it to the Lanthanides.
Yeah yeah, but why? What makes technetium’s nucleus unstable? Quarks? Strings? Bongs? Why? How?
It’s almost redundant to say that it doesn’t exist in abundance because it isn’t stable. Because it has a short half-life it decays. But why does it have a short half-life? And how many books of calculus do I have to master in order to understand the answer?
Most nuclides (nuclide:isotope:twin) are unstable. The element chlorine, for example, has something like eight isotopes, of which only one is stable and seven radioactive. IIRC, tin has eight stable isotopes, the most of any single element.
Nothing beyond bismuth is stable; the existing quantities of them all derive from the breakdown of the three radioactive isotopes with half-lives greater than 100 million years: Thorium-232 and Uranium-238 and -235. But similar breakdown sequences occur farther down the periodic table, notably a sequence of five or six rare-earth-element nuclides that break down one into the other.
As it happens, technetium and prometheum have no stable isotopes, and their longest-lived radioactive nuclide does not have a long enough half-life for any of it to have survived to the present.
Interestingly, the moderately common element indium is almost totally radioactive – it has only two “stable” isotopes, in 95:5 proportions, but intriguingly, the more common one is radioactive, but with a half-life in the quadrillions of years. About 3.2x10[sup]16[/sup] years from now, indium will be vanishingly rare.
Here’s a really simple answer, and I’m sure a nuclear physicist can give you a better one. Every atom is made up of at least one positively charged proton (called an atomic nucleus), around which smaller, negatively charged electrons revolve. The atomic number of an element tells you how many protons are in the nucleus. An atom of technetium, for example, which has an atomic number of 43, has 43 protons in its nucleus. However, as I mentioned, protons have positive charges, and two particles with alike charges repel each other. Keeping the nucleus together are particles without an electrical charge called neutrons. However, an atom like technetium isn’t able to have a configuration that keeps the protons’ charges from affecting each other. So, the nucleus is weak, and protons will tend to be forced out of the nucleus, and then you don’t have technetium anymore, but another atom.
twin) are unstable. The element chlorine, for example, has something like eight isotopes, of which only one is stable and seven radioactive. IIRC, tin has eight stable isotopes, the most of any single element.