According to Wikipedia there were 72 known elements in 1919. Another 29 were found by 1955; almost one per year. By 2008 we hit number 117. Only 16 new elements found in 53 years; less than one new element every three years on average. Obviously, scientific progress doesn’t happen at regular intervals but it’s clear the rate of new discoveries is slowing.
On the one hand the tools of scientific investigation are improving. On the other, all the readily apparent elements and some of the not so apparent ones have already been discovered. So how many new elements can we expect to find in the next 50 years? Only a handful? Is there anyway of estimating just how many total elements the universe may possess?
I’m far too sleepy to write anything substantial, but you may want to read about the island of stability. We may (a big may) get a sudden surge of new elements.
What you are seeing are paradigm changes in the nature of understanding of physics. (Stealing the term from Khun.) Initially there wasn’t even a complete theory about what an element was. The theory of chemistry evolved, and the general idea of element versus compund became understood, and the elements become known. It was the creation of the periodic table that led to the clue that there might be fundamental underpinning laws of physics that gave rise to the elements. And this gave us the understanding that atomic number - the number of protons in the nucleus - was the determining parameter. At this point we had a list of elements that had been identified, and the periodic table, that had some holes in it: undiscovered but now predicted elements. Some elements are insanely rare, and it takes a lot of work to find them. But in the sense that we had a very comprehensive theory that both predicts their existence, and predicts to very fine detail their physical charaterisitcs, science was pretty well placed. But science still requires verification and validation. As a pure example of Popperian science, these are theories that are falsifiable. If the element, when finally refined and measured, differed from the prediction, there would be a massive problem for the theory. So it is very very valuable to search out each and every element, no matter how insanely rare. So far the theory has always been right. But find something that doesn’t fit, and you probably get a free trip to Stockholm.
However the list is open ended. It starts at 1 (Hydrogen) but in principle has no upper limit. But atomic physics does provide a limit - as the nucleus gets bigger it gets more and more unstable. To the point where the chance of the nucleus remaining in existance for more than a tiny fraction of a second is very slim. These elements are made in nuclear accelerators, and are often only detected as a few individual atoms. The biggest we find in nature is Uranium.
The deal is: an element isn’t discovered until you actually have some and have measured it.
So, we had the easy elements, well known before the advent of chemistry. The elements that were discovered as chemistry become a hard science. The elements that were predicted by the periodic table, and slowly filled in by chemists. And the transuranic (elements heavier than Uranium) that were created with the atomic age. Initially easy ones, like Neputunian and Plutonium. And how harder and harder ones to create. One that have shorter and shorter half lives, and take some serious technology to detect. As mentioned above, there is a theoretical prediction that at a given atomic number the nuecleus will become somewhat more stable. But it is a long way out, and we don’t have the technology to make atoms that big yet.
In general we have discovered all the elements that exist. The insane transuranics are more a side show of high energy physics. But since they are elements, we count them, and you hear about the discoveries. But these discoveries are not unexpected. They are much more “yay we finally worked out how to make some” than Eureka moments. We knew what the elements were going to be a very long time ago. However until you have some in your lab, and can prove you had it and measured it - you don’t get to name it - and the element resides in the periodic table as a number only.
Except that we can’t measure the properties of the 110-plus elements, at least not in the same sense that we can measure hydrogen or iron. These super-high artificially created elements only last a tiny fraction of a second, far too short to measure any of their chemical bulk physical properties. We can study their nuclear properties, but those aren’t predicted by the periodic table. As far as chemistry goes, we finished discovering new elements quite some time ago, because all of the new ones can’t really be said to have chemical properties.
I couldn’t tell from the wiki article: are there any genuinely stable elements among those not yet synthesized from the island of stability? If not, do any have long half-lives? Would they all be highly radioactive?
Well, as an example, ununquadium-298 ([sup]298[/sup]114) is predicted to have a half-life of the order of 10 minutes. It’s unlikely to replace aluminium in the drinks-can industry.
This may be a dumb question but what really seems bizarre to me is why are all the natural elements Hydrogen to Uranium found on the Earth? With the chaotic disbursement of chemical elements by supernova throughout the cosmos it seem a remarkable coincidence that all of the elements on the periodic table could wind up on our planet, you would think a few would be missing or would be out there in space totally missing our solar system.
In addition could any of the man made elements like Einsteinium say be manufactured by a natural process even in theory? What has man done in the creation of these elements what mother nature cannot reproduce?
It’s not much of a coincidence at all, if you make the reasonable assumption that the gas and dust that coalesced to form the Earth was fairly well-mixed and characteristic of the natural distribution of elements in the universe. Note the the small, rocky planets like Earth were not large enough to retain much of the most common, lighter elements (like hydrogen and helium). Those planets that were large enough held onto these elements became the gas giant planets.
Sure, the transuranic elements could be created in a supernova. However, because of their relatively short half-lives, they don’t last long after the event that created them.
What man has done is to construct nuclear reactors, and devices that can bombard lighter elements with neutrons.
There were actually two elements (#43 technetium and #61 promethium) with low atomic numbers below that of uranium that were not found on earth. That was because they have no stable isotopes and none with long half lives.
I believe that none of the elements from #84 polonium on have stable isotopes, but either they are long-lived or they eventually appear as decay products of uranium and its decay products. Some of the isotopes of uranium (especially U-238) have half lives in the billions of years and so are constantly replenishing the ones below it. Beyond that, there are no long-lived elements, although #94 plutonium gets is relatively long-lived, which, I think, is why nuclear waste is so hard to deal with and why there are continual schemes for reprocessing it to use as reactor fuel leaving only relatively short lived decay products. But this is not the place to get into that argument.
This is actually fairly close to what I’d have said.
There are 78 stable elements found in nature, a small fraction of a couple of them being made up of relatively long-lived radioactive isotopes (carbon-14, rubidium-87, potassium-40, etc.). The most massive of these is Bismuth, element 83.
Then there are three elements that occur in nature with extremely long-lived “metastable” nuclides:
[ul][li]Thorium (AtomicNumber90) is naturally almost completely Th-232, with a half-life of 14 billion years, so weakly radioactive that it is safe to use as thorium-white paint.[/li][li]Uranium (AN92) has three natural isotopes: U-238 (99.3%) with a half-life of 4.5 billion years, U-235 (0.7%) with a half-life of 713 million years, and U-234 (0.0054%), with a half-life just under a quarter million years, an example of a relatively short-lived isotope that occurs naturally only because it is a breakdown product of a metastable isotope (U-238).[/li][li]Indium (AN49), not usually thought of as a radioactive element and mostly non-toxic, has two isotopes. The rarer, In-113 (4.3%) is stable, not radioactive. The more common one, however, In-115 (95.7%), is metastable with a half-life four orders of magnitude greater than the age of the universe (4.4x10[sup]14[/sup] years).[/ul][/li]
As our resident psychohistorian notes, technetium (AN43) and promethium (AN61) do not occur in nature in more than trace amounts, since they have no stable or metastable nuclide, nor are they a breakdown product of a metastable nuclide. (Promethium has been observed in the spectra of some stars, where it is presumably produced by natural bombardment of atoms neighboring it on the periodic table.)
The elements with atopic numbers 84-89, 91, and 93-94 occur in nature in varying small concentrations. Though they have neither stable nor metastable isotopes, they are stages in the breakdown of uranium or thorium (and neptunium [AN93] and plutonium [AN94] occur in trace amounts due to neutron capture by U-238 and beta decay.
The elements above plutonium are not known to occur in nature (except that an isotope of californium has been observed briefly in the spectra of supernovae).
So for all practical purposes it can be said that every element that can be “discovered” – found in nature – already has been. Beginning with americium (AN95) and from there on up, elements are not ‘discovered’ but ‘created’ by bombardment of heavy nuclei in cyclotrons, linacs, and similar high-energy-ohysics devices. Even the ‘island of stability’ is not expected to produce no stable or metastable nuclides, only ones whose half-life, though short, is long enough to identify the resulting element.
The upper limit has to be the number of protons in the universe, right? A priori there cannot be an element with more protons than exist. This site estimates 10^78 protons in the universe. But where is the physical limit you describe? Could there be an element with a million protons? Do we even know?
Black holes and neutron stars impose a limit long before you get to the number of protons in the universe.
But either there’s some nuclear bonding principle we’re missing, or atoms with more than about 300 nucleons are just very unstable. I suppose anything is possible for some fraction of a second, though.
In the nucleus, protons and neutrons are held together by the “strong nuclear force”, which is very strong but operates only at very small distances. IANAphysicist, but I presume that the reason that all elements at the upper (heavier) end of the periodic table are unstable is that their nuclei are large enough so that the electric charge of the protons, which tends to make them repel each other, overcomes the strong nuclear force. (That is, the protons on opposite sides of the nucleus are so far away from each other that the strong nuclear force attracting them to each other is weaker than the electric charge repelling them from each other.) The heaviest elements so far “discovered” (or, more accurately, created) are so unstable that they break down into lighter elements within unimaginably minute fractions of a second. So the limit you are speaking of has, for all practical purposes, already been reached. (Unless the “island of stability” proves real, in which case a limited number of much heavier elements might be possible.)
Ok…I haven’t thought about Chemistry for many Muons, but I remember being told that radioactivity was because large atomic nuclei grew too big that the strong nuclear force (or was it the weak nuclear or both) weakened at the distance and so it could no longer bind the atom together.
I had always been under the impression that many elements were formed in the earth through various means, during its formation or evolution. I don’t recall being taught this, so maybe I just always assumed so.
I recently saw where all the elements were created in stars, and the earth and everything on it, came from star stuff.
If elements were formed in the stars, how did they get in the earth in certain areas? For instance, how did the gold created in the stars stuff, which then formed earth, come to be found only in certain parts of the earth?
Maybe I am missing something here, so please enlighten me.
It’s simplistic. I found some Wikipedia links that don’t look too hard for a general reader. (I’ve found some Wiki pages that are a real slog - I think the page on “charge” is one such.)
I think it’s sad that element 114 wasn’t more stable. If superheavy elements don’t work out where will Star Fleet get their various kinds of unobtanium?
For one thing, remember that the Earth was liquid when it formed, with all of these things melted, and they tended to separate out by density. This would lead to all of the heavier elements being stuck down in the core (which, for the most part, they are), but volcanoes still stir things up a bit, and asteroid impacts also leave some core material (from the core of the asteroid) near the surface (in fact, over half of the nickel mined in the world comes from a vein resulting from a single asteroid impact, long ago).
Vulcanism and plate tectonics. Crust is melted, then depending on how things cooled the various element precipitated out at different temperatures/locations, forming veins of ore. They’ve been cycled through the heat of the earth.
In addition to plate tectonics and volcanism, you have two other major influences on the distribution of things in the Earth.
First, crystallization works to collect some materials into discrete chunks. The old salt crystal on a string science experiment is a good example - as water evaporates, the salt crystallizes onto existing salt crystals on the string. Rather than forming small crystals everywhere, you get one big crystal. Granite is a good example of this happening in rock - the longer the granite took to cool, the larger we expect the white and black crystals to be.
Second, many of the resources on the Earth are believed to have been laid down by specific processes at specific times. Iron was once distributed in a dissolved state throughout the oceans. As oxygen was produced by plant life, it oxidized the iron, which settled at the bottom of the oceans. The result is iron-rich deposits in certain places. Coal seams are probably the result of dense layers of dead vegetation that did not decompose.