How Common Are The Chemical Elements?

 

Chemistry Is Awesome!

 

Nobel Prizes 2020 (Chemistry and Physics and Medicine)

The Nobel Prize in Physics was awarded for major discoveries in black hole physics that are now mostly old news.  Past awards are listed here.

Penrose (who is still a leader in theoretical general relativity) won half for drawing the theoretical conclusion that black holes existed (subsequently born out by observations) from the equations of GR in 1965. Einstein didn't think that this conclusion could possibly be correct. Stephen Hawking was a collaborator with Roger Penrose on this work, but you have to be alive to qualify for the Nobel Prize and Hawking recently died.

Genzel and Ghez won for finding the black hole at the center of the Milky Way in the early 1990s.

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics 2020 with one half to Roger Penrose, University of Oxford, UK “for the discovery that black hole formation is a robust prediction of the general theory of relativity” and the other half jointly to Reinhard Genzel, Max Planck Institute for Extraterrestrial Physics, Garching, Germany and University of California, Berkeley, USA and Andrea Ghez, University of California, Los Angeles, USA “for the discovery of a supermassive compact object at the centre of our galaxy”.

Roger Penrose used ingenious mathematical methods in his proof that black holes are a direct consequence of Albert Einstein’s general theory of relativity. Einstein did not himself believe that black holes really exist, these super-heavyweight monsters that capture everything that enters them. Nothing can escape, not even light.

In January 1965, ten years after Einstein’s death, Roger Penrose proved that black holes really can form and described them in detail; at their heart, black holes hide a singularity in which all the known laws of nature cease. His groundbreaking article is still regarded as the most important contribution to the general theory of relativity since Einstein.

Reinhard Genzel and Andrea Ghez each lead a group of astronomers that, since the early 1990s, has focused on a region called Sagittarius A* at the centre of our galaxy. The orbits of the brightest stars closest to the middle of the Milky Way have been mapped with increasing precision. The measurements of these two groups agree, with both finding an extremely heavy, invisible object that pulls on the jumble of stars, causing them to rush around at dizzying speeds. Around four million solar masses are packed together in a region no larger than our solar system.

Using the world’s largest telescopes, Genzel and Ghez developed methods to see through the huge clouds of interstellar gas and dust to the centre of the Milky Way. Stretching the limits of technology, they refined new techniques to compensate for distortions caused by the Earth’s atmosphere, building unique instruments and committing themselves to long-term research. Their pioneering work has given us the most convincing evidence yet of a supermassive black hole at the centre of the Milky Way.

The Nobel Prize in Chemistry went to two women who, working together, developed CRISPR, the first and most important true gene editing technique, in 2011-2012. Past awards are listed here.

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Chemistry 2020 to Emmanuelle Charpentier Max Planck Unit for the Science of Pathogens, Berlin, Germany and Jennifer A. Doudna University of California, Berkeley, USA “for the development of a method for genome editing”

Emmanuelle Charpentier and Jennifer A. Doudna have discovered one of gene technology’s sharpest tools: the CRISPR/Cas9 genetic scissors. Using these, researchers can change the DNA of animals, plants and microorganisms with extremely high precision. This technology has had a revolutionary impact on the life sciences, is contributing to new cancer therapies and may make the dream of curing inherited diseases come true.

Researchers need to modify genes in cells if they are to find out about life’s inner workings. This used to be time-consuming, difficult and sometimes impossible work. Using the CRISPR/Cas9 genetic scissors, it is now possible to change the code of life over the course of a few weeks.

“There is enormous power in this genetic tool, which affects us all. It has not only revolutionised basic science, but also resulted in innovative crops and will lead to ground-breaking new medical treatments,” says Claes Gustafsson, chair of the Nobel Committee for Chemistry.

As so often in science, the discovery of these genetic scissors was unexpected. During Emmanuelle Charpentier’s studies of Streptococcus pyogenes, one of the bacteria that cause the most harm to humanity, she discovered a previously unknown molecule, tracrRNA. Her work showed that tracrRNA is part of bacteria’s ancient immune system, CRISPR/Cas, that disarms viruses by cleaving their DNA.

Charpentier published her discovery in 2011. The same year, she initiated a collaboration with Jennifer Doudna, an experienced biochemist with vast knowledge of RNA. Together, they succeeded in recreating the bacteria’s genetic scissors in a test tube and simplifying the scissors’ molecular components so they were easier to use.

In an epoch-making experiment, they then reprogrammed the genetic scissors. In their natural form, the scissors recognise DNA from viruses, but Charpentier and Doudna proved that they could be controlled so that they can cut any DNA molecule at a predetermined site. Where the DNA is cut it is then easy to rewrite the code of life.

Since Charpentier and Doudna discovered the CRISPR/Cas9 genetic scissors in 2012 their use has exploded. This tool has contributed to many important discoveries in basic research, and plant researchers have been able to develop crops that withstand mould, pests and drought. In medicine, clinical trials of new cancer therapies are underway, and the dream of being able to cure inherited diseases is about to come true. These genetic scissors have taken the life sciences into a new epoch and, in many ways, are bringing the greatest benefit to humankind.

The Nobel Prize in Medicine was awarded for discovering the hepatitis C virus.

Drs. Harvey J. Alter, Michael Houghton and Charles M. Rice on Monday received the prize for their discovery of the hepatitis C virus. The Nobel committee said the three scientists had “made possible blood tests and new medicines that have saved millions of lives.”

Many Dinosaurs (Maybe All) Were Warm Blooded

Analysis of the chemistry of dinosaur egg shells can reveal if the dinosaur was warm blooded (i.e. in a broad definition of "warm blooded" they had an internal body temperature consistently and significantly above that of the environment) or cold blooded.

Evolutionarily, dinosaurs are between reptiles (which are generally cold blooded) and birds (which are generally warm blooded), so there is no strong reason to favor one hypothesis over the other, particularly now that we known that many dinosaurs has something like feathers. The closest widely familiar bird, evolutionarily to the dinosaurs, is the chicken.

All dinosaur eggshells analyzed to date support the hypothesis that the dinosaurs involved were warm blooded, although some had more of a differential with respect to the environment than others.

The different dinosaurs varied in how much their body temperatures were higher than their environment. The Troodon samples were as much as 10 C warmer, while the Maiasaura were 15 C warmer. The Megaloolithus samples showed the smallest range of 3 C to 6 C warmer. 

"What we found indicates that the ability to metabolically raise their temperatures above the environment was an early, evolved trait for dinosaurs," Dawson, the lead author of the study that published last week in the journal Science Advances, said in a news release. 

Whether dinosaurs were cold or warm-blooded has been a long-running debate among paleontologists. A study from 2014 suggested they were neither, occupying a middle ground.

Via CNN. 

The 2014 study isn't necessarily inconsistent with this one, because it recognized the possibility of a middle ground between warm blooded and cold blooded, which the current study doesn't appear to (and may not have a way to distinguish).

Yes, Particle Physics Is That Weird

A new comic from xkcd accurately illustrates how weird particle collider physics is in a way that the average person can understand.

Alt text: 

The most delicious exotic fruit discovered this way is the strawberry banana. Sadly, it's only stable in puree form, so it's currently limited to yogurt and smoothies, but they're building a massive collider in Europe to search for a strawberry banana that can be eaten whole.

Actually, plain old organic chemistry is almost as remarkable. One of my most memorable high school experiences (while I was a high school student in New Zealand) was producing esters from noxious seeming chemicals in the lab that smelled exactly like familiar fruits and other smells, because those smells, at their most essential levels, are these chemicals.

For example, pineapple smell is partially allyl hexanoate and ethyl butyrate is a chemical in the smell of pineapple, strawberry and banana.

The Periodic Table Elements In Chinese

The world's most comprehensive English-Chinese character translation key for the Periodic Table of the elements is now available at the Language Log blog.

There are several instances where the Taiwanese representation and the People's Republic of China representation differ.  Mandarin Chinese seeks to represent all of the chemical elements with a single syllable.

New Finding Hints At Common Mechanism in Alzheimer's And Autism

The amyloid precursor protein is typically the focus of research related to Alzheimer's disease. However, recent scientific reports have identified elevated levels of the particular protein fragment, called, sAPP-α, in the blood of autistic children. The fragment is a well-known growth factor for nerves, and studies imply that it plays a role in T-cell immune responses as well.

From here.

Abnormal immune function has been noted in children with autism before, but no cause had previously been identified. The new study suggests that this protein that is already a biomarker for Alzheimer's disease may also be a biomarker for autism. Alzheimer's disease is the most well known form of geriatric dementia, although pre-clinical signs of it may start to manifest as early as young adulthood.

Autism is typically first diagnosed in preschool children and narrow definition autism is a characteristic subtype of developmental disability found in 1 in 110 children that disproportionately affects boys that is part of an "Autism spectrum" that is found in more children and at the milder end is sometimes described as a form of mere neurodiversity.

The research suggest that it may be possible in a few years to do a blood test for autism, allowing for earlier diagnosis, which could be helpful if earlier treatments have a better chance of being effective, and could also reduce the risk of misdiagnosis leading to inappropriate treatment.

Adding To the Fundamental Particle And Periodic Tables

The Periodic Table

The periodic table of the elements is old news (some interesting variant typographic representations of it exist, by the way), but I'll summarize it anyway.

Particles with the same number of protons bound together in a nucleus by the nuclear binding force have the same number of electrons in orbits around them, and as a result, have similar chemical properties. This group of similar atoms is called an "element" with a particular atomic number. Different elements can have different numbers of neutrons, which are called "isotypes" of the element. Apart from their mass per atom and their varying likelihoods of decaying into something else, isotypes of the same atom behave identically chemically.

Electrons arrange themselves around atoms in concentric "shells." For elements 1-118, there are up to four subshells (S, F, D, and P) for each of the seven periods. An additional shell (G) is theoretized to exisst for elements of atomic number greater than 118. Hydrogen and helium have only the S shell. Atoms 3-18 (Lithium to Argon) have both S and P shells, and the P shell is the outer shell. Elements 19-54 (Potassium to Xenon) also also have the D shell. Elements 55-118 (all discovered elements from Cesium on up) also have an F shell. The chemical properties of elements are determined mostly by the number of unfilled positions in the outermost (a.k.a. valence) shell.

For example, all elements with full valence shells are noble gases that are extremely unreactive chemically; those with just one electron vacancy in their outermost P shells are highly reactive halogens. Alkali metals have one electron in their outermost S shell, and Alkali earth metals have full outermost S shells. Ordinary transition metals are filling their outermost D shells. The inner transition metals (lanthanides (lanthanoids) and actinides (actinoids)) are in the process of filling their outermost F shells. The post-transition metals, metalloids and non-metals are in the process of filling their outermost P shells.

Some isotypes are unstable and their neutrons have a particular likelihood of decaying into a proton and additional decay products (beta decay), or jettisoning a group of nucleons together (alpha decay), because the nuclear binding force isn't sufficient to hold them together is a stable way. The resulting new number of protons turns the old isotype of one element into an isotype of another element with a lower atomic number. Atomic nuclei can be split in other ways too, which is called nuclear fusion and emit energy if the binding energy of the larger atom is larger than the binding energy of the smaller atom. Atomic nuclei can also be forcibly joined at high energy and if the binding energy of the resulting atom is less than the binding energy of the joined atom nuclear fusion releases atomic energy.

Generally speaking, binding energy per nucleon declines through iron (atomic number 26), and increases thereafter. So, atoms heavier than iron can be split to create nuclear energy, while atoms lighter than iron can be fused to create nuclear energy.

All elements beyond 94, plutonium, do not occur in nature (the last two elements to be discovered in nature were francium discovered in 1940 and plutonium which was synthesized in 1940 but discovered in nature in 1971), although only artificially synthesized examples produced in 1939 or later of the twenty four elements 95-118 and element 93 (neptunium) exist. Elements with atomic numbers greater than 82 (lead), as well as technetium (43) and promethium (61), have no stable isotopes and neither technetium nor promethium are found in nature although they have been synthesized.

There is no generally accepted theoretical limit to the maximum atomic number that a synthetically made atom can form. No chemist or physicist seriously doubts, for example, that we can create element 119.

There is some argument over what chemical properties the heavier synthetic elements would have, particularly beyond atomic number 138, and there is a great deal of interest in locating "islands of stablity" consisting of synthetic elements that are metastable relative to the elements that came before them in the vicinity of atomic number 126, although no one really expects to discover any more completely stable isotypes, in addition to the 255 known stable isotypes of elements greater than 82. Another 84 isotypes are found in nature but have observed radioactivity.

In general, the higher the atomic number an element has the less stable its isotypes, and isotypes tend to be less stable as they acquire more or fewer neutrons than the most stable isotype of an element. Reasoning extrapolating the causes of this growing instablity in fundamental physics have hypothesized that the maximum atomic number may be 130-173. "The light-speed limit on electrons orbiting in ever-bigger electron shells theoretically limits neutral atoms" to an atomic number of approximately 137 in a Bohr model of an electron, although considering the Dirac equation which takes into account relativistic effects, it might be able to have as many as 173 electrons coherently around an atom. Nuclei with more protons than this might be possible only as electrically charged ions, as they couldn't maintain their full electron shells.

But, the issue is largely academic because as the table of nuclides (i.e. isotypes) indicates, atoms with more nucleons become more unstable anyway. No isotype of atomic number 106 or greater has a half life of as much as a day. All but 905 of about 3000 experimentally characterized isotypes have half lives of less than an hour.

The 2400 well characterized isotypes with half lives of less than one hour are all synthetic, as are 556 isotypes with half lives of more than one hour. The longest lived isotype of atoms of atomic number 118, for example, are a bit less than a millisecond (i.e. 10^-3 second). Heavier isotypes would decay more quickly.

Fundamental Particles

The known synthetic elements, all made up of ordinary protons and neutrons, last much longer than any of the unstable fundamental particles (i.e. second or third generation fermions, W bosons and Z bosons), the longest lived of which, the muon, has a mean lifetime of about 10^-6 seconds (although in fairness, accurate estimates for muon neutrinos and tau neutrinos are not available). No hadron other than a proton or a neutron lasts longer than about 10^-8 seconds.

Most "exotic" atoms, such as muons hydrogen, are as unstable as their exotic component, although in principle, anti-hydrogen made up entirely of antiparticles, ought to be more stable so long as it is kept away from ordinary matter.

Fourth generation quarks (conventionally labeled t' and b') would presumably be significantly heavier than the top quark (about 174 GeV) and they are experimentally excluded for the b' below 199 Gev and for the t' below 256 GeV, would presumably have a half life of quite a bit less than 7*10-25 seconds and thus would presumably not hadronize, and presumably, like the top quark, the t' would almost always and instantly decay to a W+ boson and a bottom quark, while the b' would almost always and instantly decay to a W- boson and a top quark (with the antiparticles, of course, experiencing the reverse reaction).

Thus, in a collider, a t' looks just like a top quark decay with additional very energetic W+ and W- boson decays (although not energetic enough to give rise to t' and anti-t' pairs), and a b' looks just like a top quark decay with an additional very energetic W- boson decay (although not energetic enough to give rise to t' and anti-t' or b' and anti-b' pairs). Neither the t' nor the b' would give us anything more interesting than these decays, although W bosons of these energies might be expected to produce fourth generations leptons as well.

If the t' to t quark mass ratio were similar to the t quark to c quark mass ratio, one would expect the t' quark to have a mass of 20 TeV; the b quark to s quark ratio would imply a t' quark mass of 7 Tev; the s quark to u quark mass ratio would imply a t' quark mass of about 3.5 Tev; the tau to muon mass ratio would imply a t' mass of about 3 TeV. The ratio of c quark mass to u quark mass, or of muon to electron mass would suggest an even greater t' mass.

Of the b/c, c/s, and s/d mass ratios, none are smaller than a factor of about 3, so one would expect a b' mass of not less than about 522 GeV and much heavier masses on the order of 1 TeV or more would be plausible given expectations for the t' mass.

The lower experimental bound on a tau prime (i.e. fourth generation lepton) mass is about 100 GeV, which is about 55 times the tau mass, and d/s/b type mesons appear to tend to be within an order of magnitude of mass of their same generation charged lepton, so a mass in the high hundreds of GeV would not be particularly unexpected.

These values are not updated for the latest 2011 LHC bounds, which are higher. LHC puts a lower bound on the b' mass of 385 GeV, and the puts a reasonably expected t' mass values, if there is a t' quark, higher.

One possibility that could explain the thus far observed three and only three generations of fundamental fermions rule in particle physics is that there are deep reasons that prohibit particles that decay faster than W boson, a bound that the top quark already approaches and that any heavier quark would likely exceed.

Another possibility would be that there is some fundamental limit on the amount of energy that a W boson can hold. For example, the combination of the short lifetime of a W boson and its high mass translates into a maximum amount of kinetic energy or wavelength for the W boson (does a W boson or Z boson or gluon have a frequency in the way that a photon does?), that might be on the order of c (3*10^8 m/s) times the half life of a W boson (3*10^-25 s), which would be about 10^-18 meters, which is the approximate effective range of the weak force.

We know that a Z boson can give rise to a top/antitop pair with a combined mass of 348 GeV which far exceeds the 90 GeV of the Z boson rest mass. But, perhaps at some point there is a limit, and if that limitation is less than the correct mass for fourth generation fermion if there was one, then that limit would prevent fourth generation fermions from arising.

Honestly, the greatest bound on fourth generation fermions, in my mind, is the fact that we have seen Z boson decays energetic enough to produce top/antitop pairs, but have not seen any evidence of a fourth generation neutrino in the Z boson decays, which would seem to be energetically permitted up to 173-174 GeV neutrinos. All previous experience leads us to think that generations of fermions come in fours, and a 173 GeV or heavier neutrino would be so far outside the range of what we would expect given the experimental bounds on the first three generations of neutrinos, that it would seem to rule out a fourth generation of fermions entirely, and at least, would seem to rule out a fourth generation of fermions with masses low enough to be experimentally detected any time in the next century or so. The conventional statement of the experimental limitation on fourth generation neutrino mass from precision electroweak measurements is 45 GeV, which is still 2*10^6 times the approximate bound on third generation neutrino mass, when no other one generation mass increase of the same kind of fermion increases by even a factor of 10^3. (Of course, this limitation wouldn't apply to a sterile neutrino that doesn't interact with the weak force, for example, because it is is a right handed, non-antiparticle.)

If we knew the true laws of quantum mechanics better and knew they existed, we probably wouldn't care that much about finding the t' or b' or a fourth generation charged lepton experimentally. The stakes have more to do with learning the rules of the game by extending the available patterns than they do with finding that incredibly hard to create, anti-social and extremely ephemeral particles themselves. But, since we have lots of question marks about how the Standard Model functions at high energy levels, we look anyway.