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Home , Albert Ghiorso, Edwin McMillan, Eric Scerri, Friedrich Ernst Dorn, History of chemistry, Karlsruhe Congress

J. Astrophys. Astr. (2020) 41:52 Ó Indian of

https://doi.org/10.1007/s12036-020-09674-3Sadhana(0123456789().,-volV)FT3](0123456789().,-volV)

REVIEW

The

SUSANTA LAHIRI1,2,* and ASHUTOSH GHOSH3,4

1Saha Institute of Nuclear , 1/AF Bidhannagar, Kolkata 700064, . 2Homi Bhabha National Institute, BARC Training School Complex, Anushaktinagar, 400094, India. 3Rani Rashmoni Green University, Tarakeswar, Hooghly, India. 4Department of , University of Calcutta, 92 Acharya Prafulla Chandra , Kolkata 700009, India. *Corresponding author. E-mail: [email protected]

MS received 2 September 2020; accepted 21 September 2020

Abstract. In this article, a historical overview of the development of the Periodic Table has been sketched. After Mendeleev published his Periodic Table in 1869, 55 more elements have been discovered. Of these 55 elements, 35 are radioactive; most of them never existed on earlier. The excitement of the discovery of these unstable elements has been emphasized in this article. In conclusion, the dynamicity of the Periodic Table and its future have been projected.

Keywords. Periodic Table———inert elements——superheavy elements.

1. Introduction but spreads over physics, biology, , molecu- lar , technology, and even . In fact, A search for ‘‘The Periodic Table’’ yielded the Periodic Table crossed the boundary between 13,00,00,000 entries in 0.48th of a . UNESCO science and humanities when historians and sociolo- declared the year 2019 as the International Year of the gists became interested in knowing the catalytic action Periodic Table (IYPT). According to IYPT ‘‘The of society for such a development in science. Periodic Table of chemical elements is one of the The chemical elements act as a bridge between most significant achievements in science’’. IYPT-2019 Earth and astronomical objects. Billions of years of was formed by the support of the International Union galactic history is embedded in the chemical elements. of Pure and Applied Chemistry (IUPAC) in associa- The Big Bang happened 13.77 billion years ago, and tion with the International Union of Pure and Applied just after 10-6 of a second, quark-to-hadron transition Physics (IUPAP), the European Association for took place, creating and . The deu- Chemical and Molecular Science (EuCheMS), the teron, and were created one second International Council for Science (ICSU), the Inter- after the Big Bang. Along the timeline, about 4.5 national Union of History and Philosophy of Science billion years ago, Earth, perfect for sustaining and Technology (IUHPS) and the International life as we know it, was born. Apart from plenty of Astronomical Union (IAU). The official partnership and in the form of water, Earth for celebrating 150 years of the Periodic Table of contained several elements like Si, Al, Fe, Ca, Na, K, chemical elements itself signifies that the impact of Mg, Ni in its crust, mantle and core (Lutgens and the Periodic Table is not only restricted to chemistry, Tarbuck 2000). One of the major sources of Earth’s internal heat is . The primordial radioisotopes, like 40K, 238U, 235U, 232Th, were pre- This article is part of the Topical Collection: Chemical sent from the birth of this planet. Interaction of cosmic elements in the : Origin and evolution rays with the upper atmosphere of Earth produced 52 Page 2 of 18 J. Astrophys. Astr. (2020) 41:52

10Be, 14C, 26Al, 36Cl, etc. , interplanetary of many . , an expert in the dust from the asteroid belt, and cometary clouds (like , particularly the , Kuiper belt) injected many elements into Earth. Some described the discovery of the Periodic Table as a case nearby (SN) explosions might also have of ‘‘simultaneous discovery’’, or a collective phe- injected SN-produced like 182Hf, 146Sm, nomenon involving many individuals (Scerri 2015). etc. Therefore, all the elements known today (except The 1860 Congress, the first international some which were never present on our Earth or in the chemistry conference, was the indirect inspiration or Universe) were present since the beginning of Earth. source of the idea of a periodic system of elements. About 3.8 billion years before the origin of life on However, the similarities between chemical elements this Earth, 2.5 million years BP humans evolved in were observed by many scientists for a long time Africa and about 200000 years before Homo Sapiens earlier. For example, in 1827, German evolved in East Africa. Only 70000 years before Do¨bereiner started to work on chemical periodicity. Homo Sapiens evolved to a more elaborate structure He proposed ‘‘triads of elements’’, three elements of called cognitive revolution. The revolution similar properties, with the middle element’s atomic took place 12000 years BP. Permanent settlement weight (AW) approximately the average of those of the started from the time of agriculture revolution (Harari other two (e.g. Li, AW = 7; Na, AW = 23; K, AW = 39). 2015). What about elements? Did Homo Sapiens But he could not many known elements at that recognise the elements and their ? time by this series. The people of the Harappan civilization (2600 BCE) The was organized mainly on used and . and rings were the initiative of Kekule´ along with two colleagues. At common artefacts in Mohenjo-Daro, Shahr-i-Sokhta the time of the Congress, ’s (i.e. (3200–1800 BCE) and other old civilizations (Law are the smallest building blocks of chemical 2005). Three varieties of lead (PbO, PbCO3-PbSO4 and compounds) was widely accepted. However, there was PbS) were found at Harappa and these were used to much confusion about the relative atomic weights of make different varieties of pigment. The dancing the elements. The Congress was called to settle the figure of Mohenjo-Daro is a famous historical artefact. confusion regarding the concepts of ‘‘’’, ‘‘- The first in history were found in the seventh cule’’ and ‘‘equivalence’’. Well-known such century BCE in western (Harari 2015). Many as Bunsen, Cannizzaro, , Lothar elements including their uses were known from the Meyer, and many more attended the Congress. The beginning of civilization. For the rest of the elements, gathering of many chemists had a catalytic effect on humans had to wait many centuries, till science was the development of the periodic system of elements. developed and more elements were discovered by sci- According to Lothar Meyer, ‘‘the congress was very entists. is claimed to be the ‘‘first discov- useful, and undoubtedly helped to a large extent in the ered’’ element, in 1669 in Germany. development of the periodic system of the elements’’. In the universe, the lighter elements were created first, Mendeleev wrote, ‘‘the meeting produced a remark- and then the heavier elements. Hydrogen was created at able effect on the history of our science that I consider the time of the Big Bang; the deuteron was created just it a duty … to describe all the sessions ….’’. Alan one second after the creation of hydrogen. Interestingly, Rocke, a historian of chemistry at Case Western this order is not seen in the chronology of the discovery Reserve University, USA, described the 1860 Karl- of elements. The lightest element was unknown till sruhe meeting thus: ‘‘the result of the conference—the 1766, when Cavendish, a British and Periodic Table—came to fruition’’ (Mo¨nnich 2010; chemist, demonstrated the (hydro) Evert 2010). In the Karlsruhe Congress, an accurate forming (gene) gas, ‘‘hydrogen’’. The heavier form of list of atomic masses was made available by famous hydrogen, (in today’s terminology of Italian chemist Cannizzaro, which was the key factor hydrogen), was discovered in 1931 at Columbia behind the discovery of the Periodic Table. In fact, at University by the American physicist, chemist and least six scientists from different countries, with dif- Nobel Laureate . A timeline of the discov- ferent languages, came with the idea of the Periodic ery of elements is shown in Figure 1. Table over a span of nine years! UNESCO celebrated 2019 as 150 years of Men- The first significant advance towards the periodic deleev’s Periodic Table. Interestingly, Mendeleev alone system of the elements was published in 1862 by a cannot be credited for conceiving the idea of periodic French geology professor, Alexandre Be´guyer de properties of the elements; it simultaneously came to the Chancourtois. The three-dimensional arrangement of J. Astrophys. Astr. (2020) 41:52 Page 3 of 18 52

is dependent on their relative . , FRS, professor at Oxford and an English chemist, published a Periodic Table with 57 known elements in 1864 (in 1864 Newlands had included only 24 elements). Odling was one of the attendees at the Karlsruhe Congress and was a great follower of Cannizzaro. Unfortunately, Odling failed to convince the chemist community about his Periodic Table and possibly under frustration he gave up this mere clas- sification of the elements and concentrated on more fundamental science, by his own judgement (Scerri 2015). An unconventional and unique periodic chart of the elements was published in 1867 by a German-Amer- ican , Gustavus Hinrichs, professor of , chemistry and modern languages at the University of Iowa in the US (Wikipedia 1). The word ‘‘unique’’ can be applied to Hinrichs in multiple ways. Wisdom and thinking on a periodic system of the elements was mainly concentrated in Europe. Hinrichs Figure 1. Timeline of the discovery of a few chemical in that is the first one outside Europe who joined elements. this school. Moreover, he is probably the only one who arranged the system in a circular way and included similar elements in a group in the form of the periodicity of elements presented by him is spokes on a bicycle wheel (Scerri 2013). The ele- known as ‘‘telluric screw’’. In this arrangement, the mental groups described by Hinrichs were highly atomic weights of the elements were plotted on the rational. For example, he correctly placed Cu, Ag and outsideofacylinder.Onecompleteturncorre- Au in one group; even Mendeleev neglected this spondedtoanatomic-weightincreaseof16,andthe aspect in his earliest table of 1869. element obtained after the complete turn of the It would be nice if we could refer to Mendeleev’s cylinder was similar to the element before turning the Periodic Table with the prefix ‘‘finally’’: ‘‘Finally, cylinder. The telluric screw did not explain the Mendeleev published his Periodic Table correcting all similar properties of all the elements known at that the shortcomings of other Periodic Tables’’, and so on. time. Nevertheless, it was the first attempt to develop But it did not happen. One German chemist, Lothar the Periodic Table. Meyer, published his Periodic Table in 1870, only a John Alexander Newlands, a British chemist, was few months after Mendeleev published his first ver- the first person to arrange the elements in the order of sion of the Periodic Table. Both Mendeleev and their masses and ultimately published the Periodic Lothar Meyer were unaware of each other’s work Table in 1865. Newlands’s Periodic Table (Figure 2) though both of them were students of Bunsen. The is based on the ‘‘law of octaves’’, according to which peer community gave credit to both Lothar Meyer and every eighth element in the table is similar to the Dmitri Mendeleev for conceiving the idea of the corresponding first element. Newlands arranged the Periodic Table. Both of them were awarded the Davy then known elements into seven groups with eight of the Royal Society (London) in 1882 ‘‘for rows in his table. Unfortunately, the society and the their discovery of the periodic relations of the atomic peer community were not ready to accept the periodic weights’’. properties of chemical elements at that time. His The world celebrated 150 years of Mendeleev’s contribution was recognized much later, when, in Periodic Table, despite the fact that Mendeleev (in 1887, The Royal Society conferred the Russian Dmitry Ivanovich Mendeleyev) has not dis- on him. covered a single element. All he did was to make a There are at least two forgotten heroes who for- table and put the elements in the small squares of the mulated the Periodic Table in their own way—keep- table. Mendeleev took nine years from the Karlsruhe ing the central theme the same, periodicity of elements Congress to publish the first Periodic Table in 1869 52 Page 4 of 18 J. Astrophys. Astr. (2020) 41:52

Figure 2. Newlands’s Periodic Table, 1866.

(Figure 3). But by that time, many versions of the Table looks like a repetition of the idea conceived by Periodic Table had been published by many scientists. his predecessors with incremental development. But it The basis of earlier Periodic Tables was the relative is the opposite. It is a leap in science which has atomic mass, what Cannizzaro provided on the last covered almost all disciplines and has inspired great day of the Karlsruhe Congress. Mendeleev’s Periodic scientists over the years, decades and centuries since. Table, which he named ‘‘Periodic Table of the UNESCO described Mendeleev’s Periodic Table as ‘‘a Chemical Elements’’, was also based on the relative unique tool, enabling scientists to predict the appear- atomic mass of the elements. In 1869, he arranged all ance and properties of on the Earth and in the the then known 63 elements by increasing atomic rest of the Universe’’. In 1905, Mendeleev received weight in several columns. the highest award of the Royal Society, the Copley In 1871, Mendeleev formulated the ‘‘law of peri- Medal, ‘‘for his contributions to chemical and physical odicity’’ and published an improved version of the science’’. Mendeleev was elected a foreign member of Periodic Table (Figure 4). Mendeleev’s Periodic the Royal Society, the National Academy of Sciences,

Figure 3. First Periodic Table published by Mendeleev in 1869. J. Astrophys. Astr. (2020) 41:52 Page 5 of 18 52

Figure 4. Periodic Table published by Mendeleev in 1871.

USA, and the Royal Swedish Academy of Sciences. in Mendeleev’s Periodic Table. (ii) 1898–1905: The major reason for this is that Mendeleev not only 1898 is the most remarkable year in the history of classified the known elements in his table, but also science, radioactivity was discovered. Simultane- indicated some blank places where then undiscov- ously two elements, radium and polonium, took ered elements could be placed along with their place in the Periodic Table. Inspired by Curies, physical and chemical properties (Figure 5). In 227Ac was discovered in pitchblende, 222Rn and Mendeleev’s own words: ‘‘We must expect the dis- 234Pa were discovered from radium and covery of many yet unknown elements—for exam- respectively. (iii) British physicist ple, elements analogous to and — Henry Moseley changed the concept of periodicity whose atomic weights would be between 65 and 75.’’ of elements. According to him periodicity is Had he not indicated the undiscovered elements with dependent on not on atomic mass. correct relative atomic weights, then his Periodic Mendeleev’s Periodic Table was promoted to the Table would not at all have received any additional modern Periodic Table with this new concept. attention. Instead, today Mendeleev’s Periodic Henry Moseley predicted two stable elements still to Table is one of the wonders of science. He was not be discovered. The discovery of Hf and Re between awarded (though he was nominated 1923–25 can be definitely viewed as Moseley twice, in 1906 and 1907), but celebrity scientists inspired discovery (iv) The discovery of rest of the have received the Nobel Prize by filling in the gaps or elements, Fr, Tc, At, Pm, all trans-uranium actinides the blanks in Mendeleev’s Periodic Table. Only a (except Es and Fm) and all trans-actinides elements few all-time great scientists have secured a place in were discovered by charged particle or -in- the Periodic Table, Mendeleev is one of them. His duced reactions in accelerators or reactors. Fre´de´ric name is in the same row with , Einstein, Fermi Joliot and Ire´ne Curie paved the way for artificial and Lawrence. transmutation (v) Interestingly two elements Es and The elements discovered after the publication of Fm were discovered in the debris of the first Mendeleev’s Periodic Table are shown in Figure 6. hydrogen bomb fall out. In Table 1, the discovery A careful look at Figure 6 will help one to classify of post-Mendeleev elements have been classified. the timeline of the discovery of the elements after The evolution of Mendeleev’s Periodic Table to the first publication of the Periodic Table: today’s Periodic Table is an exciting story of evolu- (i) 1869–1898: 15 elements were discovered. These tion of science, technology, humanity, scientific frus- discoveries can be designated as ‘‘Mendeleev tration and ambition, and above all, the story of great inspired’’ or inspired by the prediction of elements people. The history of discovery of each element is the 52 Page 6 of 18 J. Astrophys. Astr. (2020) 41:52

Figure 5. Chemicals used by Mendeleev kept in the Chemistry Department, St. Petersburg University, . Inset at left: Gallery where Mendeleev addressed his students. Inset at right: Mendeleev’s classroom (Photo: S. L.).

Figure 6. The elements discovered after Mendeleev published his first Periodic Table.

Table 1. Various stages of discovery of post-Mendeleev elements.

Period Elements discovered 1869–1898: Mendeleev inspired Sc, Ga, Ge, Ne, Ar, Kr, Xe, Pr, Nd, Sm, Gd, Ho, Tm, Yb, Eu 1898–1905: inspired Ra, Po, Ac Rn, Pa 1923–1925: Moseley inspired Hf, Re 1937–2010: Frederic Joliot and Fr, Tc, At, Pm, Np, Pu, Am, Cm, Bk, Cf, Md, No, Lr, Rf, Db, Sg, Bh, Hs, Mt, Ds, Irene Curie inspired Rg, Cn, Nh, Fl, Mc, Lv, Ts, Og 1952–1953: Bomb product Es, Fm

history of scientific perfection, patience and hard historical aspects have been summarized here to give work. It is impossible to depict each discovery in the readers the essence of the Periodic Table—a show of limited pages of the journal. Only some selected excellence. J. Astrophys. Astr. (2020) 41:52 Page 7 of 18 52

2. Filling the gaps: 1869–98 The inertness towards any is the striking property of the newly discovered gas. Lord The puzzle: Lord Rayleigh, an English Rayleigh continued his research with the physical physicist, was working on the accurate re-determina- properties of this gas. The 1904 tion of the density of different present in . was awarded to Lord Rayleigh for his investigations After working with oxygen, his attention turned to of the of the important gases and for his nitrogen. He isolated nitrogen gas from the air, using a discovery of , a component of air, which was method suggested by his friend—another British che- undiscovered till Rayleigh and Ramsay’s experiment. mist—Sir . Lord Rayleigh took a ser- Side by side, his colleague Ramsay’s attention was ies of data and just before disposing his work on the drawn to some unknown spectral lines, that came out density measurement of nitrogen, he thought to repeat from a gas obtained when uranium containing the experiment. But this time, nitrogen would be pre- were heated with dilute sulfuric . At first, Ramsay pared directly from , not from air. He again thought that this gas was argon. Careful observation of obtained a series of valuable observations but surpris- this spectrum lines revealed its resemblance with the ingly the density of nitrogen was less than what was reference line, which had been first observed in the observed in the previous method. The difference was solar spectrum during an eclipse of the sun in 1868 in small in magnitude, one part in thousand. This small India. Shortly after due deliberation, it was established difference is generally ignored in any experiment, or that the new line is of a new element, ‘‘helium’’. It has the average result is reported or at the best reported as been found that from the specific heat data (ratio of uncertainty of the experiment. But Lord Rayleigh was specific heat at constant volume to that of constant confident that it was not an experimental error. The ) that the helium, like argon, is also monoa- density of nitrogen obtained from air is slightly higher tomic in and it is equally inert like argon. than it is obtained from ammonia. The two alternative Therefore, the discovery of helium and argon led to explanations of the discrepancy might be: (i) the establishing the family of inert gas elements. atmosphere derived nitrogen contains a heavier gas, Looking at the Periodic Table, Sir Ramsay had a hitherto unknown or (ii) the ammonia derived nitrogen feeling that there must be at least three other elements is in a dissociated state. His friend and colleague in the series. He and his assistant collected and William Ramsay was in favour of the first explanation. investigated the gases evolved from numerous min- The dissociated state of nitrogen may be unstable. erals kept at the British Museum, various British and Therefore, Rayleigh kept the nitrogen sample for eight Scottish springs, meteorites, etc. They even months, and repeated the experiment. The result was made an expedition to the spa village of Pyrenees in the same. The nitrogen derived from ammonia was to collect the gases from the hot springs. A slightly lighter than the atmospheric nitrogen. series of fractional of all the gases col- The next task was to identify the unknown heavier lected from different parts of the world resulted in gas in atmospheric nitrogen. The task was carried out mere frustration. Only some of the collected fraction by Ramsay and Rayleigh, initially independently, and showed spectral lines of helium and argon, those later in concert. Both of them adopted multiple already discovered. methods in search of this unknown gas. One of the The entire years 1896 and 1897 were spent on methods is schematically presented in Figure 7. collecting 15 of argon gas. From this 15

Figure 7. A simple pictorial presentation of argon discovery. 52 Page 8 of 18 J. Astrophys. Astr. (2020) 41:52 fraction, after concentrating the gas, they were able to benefit to humankind. Immediately, the scientific find the new of a new element, community showed unprecedented enthusiasm in (the hidden one). The gas was forty times heavier than Ro¨ntgen’s discovery. Just three months after, the hydrogen, implying the atomic weight 80. On June French physicist Henri discovered radioac- 1898, the team of Ramsay announced another new tivity. By the time, a young Polish lady, Marie Sklo- gas, that has a lower than argon and dowska, joined Professor ’s laboratory in named the element as . In September 1898, Paris. Marie decided to work on uranic rays for her another new gas was discovered, by liquefying air, doctoral degree. The properties of uranic rays were till and fractionation of its components like argon, kryp- that time only qualitative. Curies wanted to measure , etc. The gas was named ‘’ or the ‘stranger’. radioactivity quantitatively by using the property of The group measured the ratio of the specific heats, of air by uranic ray. She undertook the study refractivity, densities, compressibility and the vapour on the of uranium compounds, and extended of all these gases. From all these observa- this study to other substances, including tions, they concluded that helium, neon, argon, kryp- compounds. It was found that the activity of a com- ton, and xenon are monatomic. In general terms, they pound is directly proportional to the amount of uranium concluded that these gases show a regular trend in or thorium present in the compound (Figure 8). their properties, and they fill the gaps in the Periodic The important conclusion of Marie Curie’s Ph.D. Table. , defended in June 1903, is that the radioactivity A quote from the Nobel lecture of Ramsay will help is an atomic property, which implies that the atom is to understand the colossal task, the tasks that he carried no more indivisible, and therefore, it is a milestone in out to discover and measure the physical parameters of fundamental physics. Madame Curie along with her these inert gases: ‘‘Amounts of neon and helium in air husband Pierre Curie received the Nobel Prize (shared have since been measured; the former is contained in air with Henry Becquerel) for this path-breaking discov- in the proportion of 1 volume in 81,000; the latter, 1 ery in physics. volume in 245,000; the amounts of krypton and xenon The Curie couple had some unexpected observations are very much smaller – not more than 1 part of krypton for some minerals, like pitchblende or chalcolite. These by volume can be separated from 20,000,000, of air; and minerals showed much greater activity than what was the amount of xenon in air by volume is not more than 1 expected, from the stoichiometric composition of ura- part in 170,000,000’’. nium present in the . To get rid of this puzzle, Marie The difficulty of discovery was not only the pres- prepared synthetic chalcolite (crystallized of ence of these gases in minuscule amount, but one has and uranium) from pure products, and the to imagine that there was no existence of a single measured activity of this synthetic product was con- member of this inert gas family. Even Mendeleev’s sistent with the uranium content. The Curie couple prediction excluded these elements. Sir Ramsay has to assigned the high activity of natural pitchblende again reconstruct the mental picture of the Periodic to another hitherto unknown element which has much Table and successfully discover all the elements. higher radioactivity compared to uranium. To prove the Sir William Ramsay was awarded the Nobel Prize concept, Marie and Pierre Curie, the all-time great in 1904 ‘‘in recognition of his services in the discov- , started the painstaking pure classical ery of the inert gaseous elements in air, and for chemistry experiments in a makeshift laboratory (Fig- determination of their place in the periodic system.’’ ure 9). Madame Curie continued the experiment alone after the untimely demise of Pierre Curie in 1906. Finally, in 1910, Madame Curie could isolate a few 3. Filling the gaps: 1898–1905, Marie Curie milligrams Ra from of pitchblende, and determine inspired its atomic weight accurately for which she received the second Nobel Prize. The entire work of Marie and Pierre The next part of the story has been told millions of Curie from 1898 to 1910 should be viewed in one string. times by millions of people in millions of context. Figure 10 and Figure 11 presents schematically Cur- However, the story of the discoveries by the Curies is ies’s experiment, and how they discovered polonium once again important in the context of development of and radium. Each step of this chemical separation was the Periodic Table. repeated innumerable times and the radioactivity pre- In November 1895, Wilhelm Ro¨ntgen discovered sent in each fraction was measured after each step of X-rays—the discovery that conferred the greatest chemical separation. J. Astrophys. Astr. (2020) 41:52 Page 9 of 18 52

‘radium emanation’ was vapour of thorium. Within a year, Rutherford changed his view and was in favour of the third possibility that the gas is a hitherto unknown new element. They had estimated a rough value of the atomic weight of the gas which was far less than thorium or radium. So radium emanation was first identified by Rutherford as a new element (afterwards named as ). Therefore, Rutherford is the true discoverer of radon (Rayner-Canham and Rayner-Canham 2004). Later, Ramsay and his co- worker isolated radon and determined its density, and Figure 8. The which the Curies used to radon became the heaviest of all known gases. At the measure radioactivity by ionizing the gases with the emitted same time, it was inert to chemical reactions. Rn was radioactivity. The instrument is kept at the Muse´e Curie, accommodated as the heaviest member of the inert Paris, France (Photo: S.L.). gases. Interestingly Rutherford himself gave the credit of discovery to Curies. Nevertheless, the discovery of To discover the two elements Po and Ra, to fill in Rn gave the concept of half-life, a decay and b decay, just two squares of the Periodic Table, Madame Curie etc. All these helped Rutherford investigate into the handled a huge amount of radioactivity, and as a result disintegration of elements, for which he was awarded succumbed to aplastic anaemia, caused due to pro- the in 1908. longed exposure to radiation. This history of the was first identified in 1913 by K. Periodic Table is also the history of highest level of Fajans and O. Go¨hring during the study of 238U decay humanity and sacrifice. chain. In the year 1917/18, two groups, and In 1900, , a Germany physicist, Lı`se Meitner from Germany and F. Soddy from Great reported that a gas is emitted from thorium and radium Britain, independently discovered another long-lived compounds, which is radioactive. He named this gas isotope of protactinium in 235U chain (Wikipedia 2). as ‘‘radium emanation’’. ‘‘Radium emanation’’ Figure 12 and Figure 13 show the respective protac- became a popular term to describe the biological tinium in 238U and 235U decay series. effects of radium. In the early , radium was inhaled to treat , and it was believed that radium emanation was actually responsible for killing 4. Moseley: Transition of Mendeleev’s Periodic cancerous cells (Saudermann 1911). Ernest Ruther- Table to modern Periodic Table ford became interested in characterizing radium emanation. He proposed two possibilities, either (i) Rutherford proved by his famous experiments on the this gas is fine dust particles of the radioactive sub- scattering of a-particle on foil that the mass of stances or (ii) a vapour from . It the atoms are concentrated in the nucleus which is was easily proved experimentally that the emanation positively charged and surrounded by negatively was not dust. Therefore, Rutherford concluded that the charged to make an atom electrically neutral.

Figure 9. Madame Curie’s laboratory (Muse´e Curie, Paris, France). Everything is kept unchanged except the table top – which was contaminated with huge amount of radioactivity, therefore, changed (Photo courtesy: S. L.). 52 Page 10 of 18 J. Astrophys. Astr. (2020) 41:52

Figure 10. The first part of Curies’ experiment. They failed to separate the active substance from . They wrote in their diary (1998) ‘‘we obtained a substance whose activity is about 400 times greater than that of uranium. If the existence of this new is confirmed, we propose to call it polonium from the name of the country of origin of one of us.’’

He also determined the number of positive charges on verification of this hypothesis by suitable experiments. the nucleus of gold and some other elements by a- As the results of determining the positive charge of the scattering experiments and noticed that the experi- nucleus by a-scattering experiments were not very mentally determined charges are approximately half accurate, Moseley looked for other means. At that of the atomic weight of the elements. Hence Ruther- time it was known that X-rays, produced in the ford concluded that the atomic weight should have a , are of two types: the continuous part relation with the positive charge in the nucleus and due to slowing down/stoppage of electrons and is usually higher is the atomic weight, higher is the featureless, and the few peaks having very high positive charge. He discussed this hypothesis with a intensity depending upon the metal used in the anti- new student, Henry Moseley who wanted to do Ph.D. . Moseley decided to take the photographs of under his supervision and assigned him the job of these peaks that appeared in X-rays for different J. Astrophys. Astr. (2020) 41:52 Page 11 of 18 52

Figure 11. Schematic presentation of Madame Curie’s experiment for isolation of milligram amount of radium from tons of pitchblende. The Nobel Prize was conferred to her in 1911 for isolation of radium metal, this being the first time that the distinction had been conferred upon a previous prize winner.

elements and compared them to see if these peaks are related to the positive charge of the nucleus. By per- fecting the photographic methods, he could determine the frequency of the emitted X-ray very precisely. He started with an anticathode made of aluminium and examined the X-ray spectra of thirty-eight ele- ments—from aluminium to gold. He made the fol- lowing observations: (I) X-rays of different elements are different. (II) The heavier the element, the shorter is the wavelength and higher is the penetrating power of the emitted X-ray. 234 238 (III) When the numbers of the elements, represent- Figure 12. Short-lived Pa (6.7 h) is a part of U decay series. ing their position in Mendeleev’s table is 52 Page 12 of 18 J. Astrophys. Astr. (2020) 41:52

capable of accomplishing such a remarkable piece of work. The law of Moseley confirmed in a few days the conclusions of my efforts of twenty years of patient work.’’ Arrhenius in 1915 nominated him for Nobel Prize in Chemistry as well as in Physics. But in the same year (1915) he died in war at his 27 years of age.

5. Filling the gaps: 1923–1925, Moseley inspired

In Moseley’s Table, there were rooms for elements with atomic numbers of 43, 61, 72, 75, which were 231 235 Figure 13. Long-lived Pa (32 ka) is a part of U unknown at that time (Figure 14). In 1914, the ele- decay series. ment 72, laid vacant by Moseley and also predicted by Mendeleev was reported as one of the rare earth ele- plotted with the inverse of the square roots of ments. But was much disturbed by this the vibration frequencies of their X-rays, a claim, because it was contradictory to his proposal on straight line is obtained. the electronic structure of an atom. The f-orbital can (IV) He concluded ‘‘There is in the atom a funda- accommodate only 14 electrons, so there is no place to mental quantity which increases by regular accommodate another rare earth element. He instruc- steps as we pass from each element to the next. ted his colleagues George von Hevesy and Dirk Coster This quantity can only be the charge on the at the University of Copenhagen to search for the central positive nucleus.’’ missing element predicted by Moseley in Zr ores, as it With these observations, in 1912, Moseley at his 25 would resemble . Finally, in 1923, element years of age, discovered that the positive charge in the 72, was discovered by George von Hevesy and Dirk nucleus, i.e. the atomic numbers of the elements are Coster. To honour Niels Bohr, the element was named more fundamental than atomic weight—a break- as —Hafnia is the old name of Copenhagen, through fundamental discovery in science. He pre- the birth place of Niels Bohr. Discovery of , pared a new table on the basis of atomic numbers. At element 75, was announced by Walter Noddack and that time the known element with the highest atomic Ida Tacke of Berlin in 1925. number, 92, was uranium. So from his table, it became obvious that no more than 92 elements from hydrogen (atomic number 1) to uranium (atomic number 92) can 6. Fre´de´ric Joliot-Curie and Ire`ne Curie be accommodated. His discovery also helped the proper placing of the elements which was considered They have not discovered any new element. But the anomalous in Mendeleev’s Periodic Table. For history of the Periodic Table would be incomplete if example he determined that the atomic number of the contributions of Fre´de´ric and Ire`ne Curie are not to be 19 and figured out that it should be discussed. In February 1934, Fre´de´ric Joliot and Ire`ne placed before argon although their atomic weights are Curie published a half of a page paper in Nature in reverse order. Similarly, he corrected the positions wherein they claimed the first artificial transmutation of and , and and . In the and production of new -emitting radioisotope Mendeleev’s Periodic Table, positions of the ‘‘rare 13N produced by the a-induced reaction on earth’’ were rather baffling. In Moseley’s Table, these (10B ? 4He = 13N?n) (Joliot and Curie 1934). Simi- 15 elements could be fitted unambiguously with the larly, they also produced 30P and 27Si by the nuclear atomic numbers from 57 to 71. In this context, after reactions—27Al ? 4He = 30P?n and 24Mg ? 4He = the untimely death of Moseley, the quote of the 27Si? n respectively. They were awarded the Nobel French scientist, Georges Urbain of the University of Prize in 1935 in Chemistry ‘‘in recognition of their Paris (who did remarkable work on the separation and synthesis of new radioactive elements’’. Ire`ne and identification of ‘‘rare earth’’ elements) is worthy to Fre´de´ric’s discovery not only conferred the greatest mention, ‘‘I had been very much surprised when I benefit to humankind by paving the way for the pro- visited him at Oxford to find such a very young man duction of radioisotopes for clinical use, it also opened J. Astrophys. Astr. (2020) 41:52 Page 13 of 18 52

Figure 14. The Periodic Table after Moseley in 1914 (incorporated in the modern ACS Periodic Table by the author). The four red marks indicate the four elements ‘‘to be discovered’’ predicted by Moseley. Since Moseley worked from aluminium to gold, the elements predicted by Moseley had lower atomic number than Au. up the possibility of synthesis of new elements and California designed the world’s first at the adding them to the Periodic Table. In fact, a total of 30 age of 28. In 1937, an Italian physicist Emilio Segre` elements till date have been added to the Periodic of University of Palermo, Italy, requested Lawrence Table after the discovery of cyclotron by E. for some thrown away parts of the Berkeley cyclo- O. Lawrence (Nobel Prize in Physics 1939), and the tron. Lawrence sent him a molybdenum piece used commissioning of by in the cyclotron. Emilio Segre` and his co-workers (Nobel Prize in Physics 1938). These elements do not noticed high radioactivity in the molybdenum foil. exist naturally on the Earth and can only be synthesized. They radiochemically separated a new element, the One of the authors (SL) cannot resist himself from first artificial element. The atomic number of the narrating a personal reminiscence with Professor Pierre element was found to be 43. The element was Joliot, son of Ire`ne and Fre´de´ric. When I personally met named as (technically produced). Segre` him, my very first question was, ‘‘how did your parents and his co-workers isolated 95mTc and 97Tc from the discover artificial radioactivity? The cross-section of molybdenum foil (probably produced by 4He ? 27Al = 30P?n reaction is low, the detector 95Mo(d,2n)95mTc and 97Mo(d,2n)97Tc reactions). technology at that time was in nascent stage, no show Later he visited LBNL again, and with the help of of cyclotron, and the alpha flux from natural source was Glenn T. Seaborg separated 99mTc from molybde- also minimum’’. The comment of Professor Joliot was num foil. The 99mTc is the magical radioisotope in interesting: ‘‘not only my parents, but my grandfather and annually 99mTc is adminis- and grandmother (Pierre Curie and Marie Curie) also tered to ten million patients for imaging purposes. had equal of being rejected by the scientific The discovery of technetium was rather silent and community, instead they received Nobel Prize only has not received the attention of the peer community because their numbers were correct.’’ that it deserves. It is noteworthy to mention that Mendeleev predicted eka- with atomic weight 100, even in his 1871 version of Periodic 7. 1937–2010: Filling up the gaps – Fre´de´ric Joliot Table (Figure 4). About 65 years after, the discov- and Ire´ne Curie inspired discovery ery of technetium proved the greatness of Men- deleev’s prediction. In 1914, Moseley also predicted More than one-fourth elements (30 out of 118) of the element number 43 (see Figure 14). the Periodic Table are artificially produced. The In Moseley’s table, element 85 was empty, Men- artificial transmutation discovered by Fre´de´ric deleev also predicted eka-iodine. Niels Bohr’s elec- Joliot and Ire´ne Curie paved the way for the dis- tronic theory also suggested that heaviest is covery of all these elements. In 1929, E.O. Lawr- yet to be discovered. All these again inspired Emilio ence, a young faculty of physics at the University of Segre` and his colleagues Dale Corson and Kenneth 52 Page 14 of 18 J. Astrophys. Astr. (2020) 41:52

Mackenzie to search for the heaviest halogen with the Berkeley National Laboratory (LBNL) along with his Berkley cyclotron. They discovered 211At in 1940 by colleagues like synthesized Am, Cm, bombarding bismuth with (209Bi ? 4He Bk, Cf in series. = 211At ?2n). Till date about 22 isotopes of At have [1940]: (238U ? 2H) 238Np (b)238Pu (88 a) been discovered, none of them are stable and the longest [1945]: (239Pu ? n) 240Pu(?n) 241Pu (b)241Am (432.2 living isotope of is 210At (T = 8.1 h). 211At 1/2 a) is an alpha emitter and till date it is the most [1944]: (239Pu ? 4He) 242Cm (160 d) promising for targeted alpha therapy. [1949]: (241Am ? 4He) 243Bk (4.5 h) Emilio Segre` was a celebrity physicist; his life was [1950]: (242Cm ? 4He) 245Cf (45 m) full of discoveries. He discovered two elements technetium and astatine which are serving humankind. Mendeleev put 5 dashes after uranium. Therefore, He was also the discoverer of slow neutron with the synthesis of was for the first time, Enrico Fermi, but his most fundamental discovery was beyond the imagination of Mendeleev. The Nobel antiproton, for which he was awarded the Nobel Prize Prize in Chemistry in 1951 was awarded to Edwin in Physics in 1959. McMillan and Glenn Theodore Seaborg ‘‘for their Mendeleev indicated a ‘‘-’’ dash after uranium discoveries in the chemistry of the transuranium indicating an unknown element beyond uranium. In elements’’. the 1940s, Enrico Fermi had already discovered The history of the Periodic Table is the history of slow neutrons. He bombarded uranium with these society, humanity, patience, hard work, and some- slow neutrons. 238U captured the slow neutron and times frustration. Even war had a role in the converted to 239U. Fermi believed that he had syn- development of Periodic Table. Ivy Mike, the first thesised a new element which has been formed by thermonuclear bomb was detonated on November 1, the b decay of 239U. Therefore, he reported the first man- 1952. The debris of the bomb was analysed by made transuranic element with atomic number 93. For Albert Ghiorso and his team in LBNL, and to their this, he was awarded the Nobel Prize in 1938. In the surprise, they found two new elements, the atomic meantime, in 1939, Otto Hahn, , and numbers were determined and found to be 99 and discovered fission. Soon it was realized 100, afterwards named as (Es) and that Enrico Fermi had actually observed a lighter (Fm). The power of this bomb was element caused by the fission of uranium and had not equivalent to 10 megatons TNT. The tremendous discovered element number 93. generated from the bomb, made it possible Just two years after, in 1940, after several unsuc- for the following unusual reaction. Afterwards, cessful experiments, Edwin McMillan at the Berkeley different isotopes of Es and Fm were synthesized by Radiation Laboratory, could synthesis element num- accelerator induced reactions. ÀÁ ber 93 by irradiating uranium target with a slow 253 253 238U þ 15n ðÞ6b CfðÞb EsðÞ 20:47 d neutron, using the same , 238U ? n ! ÀÁ 253 253 253 239U(b) 239Np. After the Fermi incident, Edwin 238U þ 15n ðÞ6b CfðÞb EsðÞb FmðÞ 3 d McMillan was careful and a series of painstaking chemistry experiments confirmed the new element with atomic number 93, which was later named as The element number 101 was produced in LBNL . under the leadership of G. T. Seaborg and Albert From the end of 1940, Seaborg era started in Ghiorso using following nuclear reaction: ÀÁ256 Berkeley Radiation Laboratory. Glenn T. Seaborg, a ½Š1955 : 253Es þ4 He MdðÞ 1:17 h 28 years old young nuclear chemist, bombarded ura- nium with deuteron. He along with colleagues, Edwin None but G. T. Seaborg proposed the name of McMillan, Emilio Segre` and Joseph Kennedy, iden- element number 101 as . In the time of tified and chemically isolated another new trans-ura- , it was not very easy to convince the US nium element with atomic number 94, bureaucrats to give a Russian name to a newly dis- which has been produced via 238U ? covered element. By doing that Seaborg proved again 2H!238Np(b)238Pu reaction. In the meantime, in that science has no boundary. At last the creator 1944, Seaborg has published his famous secured a position in the Periodic Table. theory. Now the numbers of actinides are fixed. The Synthesis of (atomic number 102) rest is history. Glenn T. Seaborg at Lawrence was first attempted in 1957 using the J. Astrophys. Astr. (2020) 41:52 Page 15 of 18 52 reaction 244Cm ? 13C. Later, it was found that their because extremely low production rate of superheavy claim cannot be true. Simultaneously, experiments elements and their short half-life allows chemical were carried out at Berkeley and . Albert investigation one atom at a time. The chemists wanted Ghiorso performed the experiment at LBNL by to place Rf and Db below Hf and Ta respectively. The bombarding 244,246Cm by 12C and they obtained 3 s essential criterion for this placement is that the two half-life, which was assigned to 254No. Later, FLNR new elements must have similar chemical properties studied various C ? Cm reactions and showed that with their lower homologues, i.e., Rf should resemble 254No has half-life *55 s, and that the 3 s is from the chemical behaviour of Hf and Zr, and Db should 252No. LBNL repeated the experiment and confirmed resemble Ta and Nb. that Dubna was correct. Therefore, nobelium was In this direction, systematic investigation on aqueous discovered by both LBNL and Dubna. This example chemistry of Rf through the comparative study with the shows that research with heavier elements became homologues Zr and Hf started at RIKEN. They pursued difficult due to the short half-life of the product, and chloro-, fluro-, and sulphate complex formation also the in such nuclear reactions is too low. of Rf, Hf and Zr, followed by anion-exchange or The last actinide (atomic number 103) reversed- chromatographic extraction of these was discovered in LBNL by Ghiorso, Sikkeland, complexes. For example, they studied the displacement Larsh and Latimer using the following nuclear of the metal (M = Zr, Hf, 261Rf) fluoro complexes from - reaction. the binding sites of the resin by the counter anion NO3.It ÀÁ 261 252 11 263 was observed that the behaviour of Rf was similar to ½Š1961 : Cf þ B LrðÞ 10 h their lighter homologues. In total, 3788 cycle anion exchange experiments were carried out to come to this conclusion. RIKEN also carried out a similar type of 8. Journey to the Terra Incognita experiment with Db, Ta and Nb. All these experiments conclusively placed Rf in the same group of Zr and Hf; The last element of the actinide series, Lr, was dis- Db in the same group of Nb and Ta. In nutshell, covered in 1961. What is next? Is it possible to syn- chemistry played an important role in finding a place for thesize an element after Lr? By the time, few more super-heavy elements (SHE) in the Periodic Table. centers like Gesellschaft fu¨r Schwerionenforschung, Again the very important question between various GSI, Germany and RIKEN, Japan also started research superheavy groups was, ‘‘is it possible to synthesize an on the heaviest elements. Exploration of these trans- element beyond ?’’ After seven years of the actinide elements is a very difficult task. Their syn- discovery of Sg, Darmstadt era started for the new thesis—even just one atom—is a challenge. Albert superheavy elements. A group of physicists like Ghiorso and his group (Nurmia, Harris, Eskola and S. Hofmann, G. Mu¨nzenberg, V. Ninov, F.P. Heberger, Eskol) successively reported the synthesis of elements P. Armbruster, H. Folger, etc., discovered elements 104, 105, 106 using the following nuclear reactions. number 107 to 112 in Darmstadt using the SHIP separator.

249 12,13 257;259 209 54 262 [1969]: Cf( C,xn) Rf () [1981]: Bi( Cr,n) 107Bh () 104 208 58 249 15 260 [1984]: Pb( Fe,n) 265Hs () [1970]: Cf( N,4n) 105Db () 108 249 18 209 58 266 [1974]: Cf( O,4n) 263Sg (Seaborgium) [1982]: Bi( Fe,n) 109Mt () 106 208 62 269 [1995]: Pb( Ni,n) 110Ds () Seaborgium is the first element in the Periodic Table, [1995]: 209Bi(64Ni,n) 272Rg () which has been named to honour a living scientist G. 111 [1996]: 208Pb(70Zn,n) 277Cn () T. Seaborg for his extraordinary credit of discovering 112 more than 10 elements in the Periodic Table. The elements 107 to 112 were synthesized by cold After synthesizing, pertinent questions were, what fusion, where nuclear excitation energy is low (10–20 will be the chemical behaviour of these elements? MeV), a stable target is used and generally, one Does Rf open the next series of d-elements? Can we neutron is ejected. Wherein in the hot fusion, the place them in the Periodic Table? If yes, where? nuclear excitation energy is higher (30–50 MeV), a Therefore, search for a room in the Periodic Table for radioactive actinide target is used, and generally 3–5 the newly discovered elements started. A new branch neutrons are ejected. of chemistry has been developed called ‘‘atom-at-a- The discovery of element number 113 (, time chemistry’’ (Tu¨rler and Pershina 2013). This is Nh) is credited to RIKEN though Dubna also observed 52 Page 16 of 18 J. Astrophys. Astr. (2020) 41:52 the element 113 as a daughter product of element 115 (TransActinide Separator and Chemistry Appara- at the same time. RIKEN under the leadership of K. tus). The main aim of TASCA was chemical Morita produced E115 by reaction using studies of SHE. The emphasis was set on SHE the following nuclear reaction. produced in hot-fusion reactions. The Saha Insti- tute of joined the TASCA group [2004]: 209Bi(70Zn,n) 278Nh (Nihonium) 113 in 2003; first time Indian participation in SHE The first event was observed in July 2004, the experiments. TASCA commissioning was com- second event was observed in April 2005, and the pleted in 2008. By the time, SHE research became third event was observed in August 2012. This extremely complicated, and multiple high-end demonstrates the difficulty in SHE experiments. The instruments were required for successful SHE two most important factors for this difficulty are experiments. TASCA was coupled with highly extremely short half-life of the superheavy elements. efficient Focal Plane Detector, Recoil Transfer The second bottleneck for SHE research is the Chambers (RTC), Rotating wheel On-line Multi- production rate, which also became too small for detector Analyser (ROMA) to further increase its heavier elements (Table 2). efficiency. TASCA as a whole became the most Dubna again has been credited for the discovery of versatile and highest efficient instrument in SHE elements 114 to 118 under the leadership of Oganes- researches worldwide. Since then numerous sian. Elements 114 to 118 were discovered succes- experiments have been carried out using TASCA sively using the following reactions: facility by the international collaboration known 244 48 287 as ‘‘TASCA Collaboration’’. For example, A gas [2004]: Pu( Ca, 5n) 114Fl () experiment on Fl at TASCA was 243 48 289 [2010]: Am( Ca, 2n) 115Mc () conducted earlier. (Yakushev et al. 2014). The 245 48 291 [2004]: Cm( Ca, 2n) 116Lv () experiment indicated the metallic character 249 48 293 [2010]: Bk( Ca, 4n) 117Ts () of Fl. Another noteworthy experiment was, pro- 249 48 294 [2004]: Cf( Ca, 3n) 118Og () duction and decay of element 114 (Du¨llmann et al. 2010). The names were accepted by IUPAC only in 2019 The most noteworthy experiment so far at TASCA after independent confirmation of synthesis of these is the independent confirmation of new element 117 elements. Oganesson is the second element in the synthesized through 48Ca ? 249Bk reaction (Khuyag- Periodic Table which has been named after a living baatar et al. 2014). In total, sixteen institutes all over scientist—Oganessian. There are some controversies the world joined TASCA E-117 international collab- between different research groups and IUPAC oration, including the Saha Institute of Nuclear Phy- regarding the accepted dates and the pathways for first sics, India. Element 117 was separated from many seen SHE. other nuclear reaction products in the TASCA and The SHE story would be incomplete without were identified through their radioactive decay. The mentioning the TASCA group at GSI, Darmstadt, collaboration identified two decay chains comprising Germany. In the early years of this century, GSI seven a decays and a spontaneous fission (Figure 15). Kernchemie group along with many other experts Both the a decays came from the isotope 294117 and designed and built a new device, TASCA its decay products. A new isotope of Dubnium, 270Db was discovered in the chain, whose half-life was determined as more than 1 h. The long half-life indi- Table 2. Half-life and production rates of some super- cates the possibility of discovering the ‘island of sta- heavy elements. bility’ in future. Is it possible to synthesize elements beyond 118? Half-life of the Production TASCA collaboration performed long hunts in 2011 Reaction product rate and 2012 for discovering elements 120 and 119 using 248Cm(18O,5n)261Rf 65 s 3 min-1 50Ti?249Cf and 50Ti?249Bk reactions respectively. 249 18 262 -1 Bk( O,5n) Db 34 s 2 min However, no signature of E119 and E120 was 249 18 263 -1 Cf( O,4n) Sg 0.8 s 6 h observed. 249Bk(22Ne,4n)267Bh – 1.5 h-1 248 26 269 -1 Now a days, SHE experiment is a challenge. High Cm( Mg,5n) Hs 9s 3 d energy, high current accelerators, excellent target 238U(48Ca,3n)283Cn – 1 d-1 preparation facilities, excellent separators (vacuum or J. Astrophys. Astr. (2020) 41:52 Page 17 of 18 52

chemical elements, and reactivity of Cn and Fl, organometallic compounds of Rf to Hs, reactions of Sg to Hs, atomic and ionic radii of SHE are few identified and challenging problems. It is a long search and an exciting one.

9. Conclusion

The Periodic Table is a dynamic understanding of the properties of the elements. Therefore, the cur- rent shape of the Periodic Table is not the ultimate one. For example, Sato et al. (2015) determined the first ionization potential of lawrencium. The IP of Lr was measured with 256Lr of half-life 27 . They used an efficient surface -source coupled to a mass separator. They have shown that IP1 of Lr is the lowest of all and actinides, and the disorder of periodicity started at Lr. Their work triggered a discussion in IUPAC whether Lr is the last actinide, or it is better to shift Lu and Lr in group 3 below Sc and Y?

Acknowledgements

One of the authors (SL) gratefully acknowledges Professor Christoph E Du¨llmann, the leader of TASCA group, GSI for his inputs on constructing the SHE part of this article.

References

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