Prediction of New Elements and Compounds

Newlands (1864) was the first to predict correctly the existence of a missing element when he calculated an atomic weight of 73 for an element between silicon and tin, close to the present value of 72.61 for germanium (discovered by 

Winkler in 1886). However, his method of detecting potential triads was unreliable and he predicted (non-existent) elements between 

Of the remaining 26 undiscovered elements between hydrogen and uranium, 11 were lanthanoids which Mendeleev s system was unable to characterize because of their great chemical similarity and the new numerological feature dictated by the filling of the 4f orbitals. Only cerium, terbium and erbium were established with certainty in 1871, and the others (except promethium, 1945) were separated and identified in the period 1879-1907. The isolation of the (unpredicted) noble gases also occurred at this time (1894-8). 

Colour dark grey Colour greyish-white 

M will be obtained from MO2 or K2MF6 by reac- Ge is obtained by reaction of K2GeFe with Na  

Colour dark grev Colour greyish-white 

M will be slightly attacked by acids such as HCl Ge is not dissolved by HCl or dilute NaOH but reacts  

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In addition to the prediction of new elements and their probable properties, the periodic table has proved invaluable in suggesting fruitful lines of research in the preparation of new compounds. Indeed, this mode of thinking is now so ingrained in the minds of chemists that they rarely pause to reflect how extraordinarily difficult their task would be if periodic trends were unknown. It is the ability to anticipate the effect of changing an element or a group in a compound which enables work to be planned effectively, though the prudent chemist is always alert to the possibility of... 

Before continuing the story of the discovery of the chemical elements, it will be necessary to outline the early attempts at classification made by Dobereiner, Begtiyer de Chancourtois, and Newlands, and to discuss briefly the periodic system of the elements which teas developed independently by Lothar Meijer and Mendeleev. This classification enabled Mendeleev to predict the properties of a number of undiscovered elements and of their compounds with surprising accuracy, and proved to be of great assistance in all subsequent discoveries of new elements. 

The periodic law was accepted immediately after its proposal by Mendelyeev because of his success in making predictions with its use which were afterward verified by experiment. In 1871 Mendelyeev found that by changing seventeen elements from the positions indicated by the atomic masses that had then been assigned to them into new positions, their properties could be better correlated with the properties of the other elements. He pointed out that this change indicated the existence of small errors in the previously accepted atomic masses of several of the elements, and large errors for several others, to the compounds of which incorrect formulas had been assigned. Further experimental work verified Mendelyeev s revisions. 

Theoretical chemical research on the heaviest elements is not less challenging than the experimental one. It should be based on the most accurate relativistic electronic structure calculations in order to reliably predict properties and experimental behavior of the new elements and their compounds. It also needs development of special approaches that bridge calculations with quantities that cannot be so easily predicted from calculations. Due to recent spectacular developments in the relativistic quantum theory, computational algorithms and techniques, very accurate calculations of properties of the transactinide elements and their compounds are now possible, which allow for reliable predictions of their experimental behavior. These theoretical works are overviewed here. Special attention is paid to the predictive power of the theoretical studies for the chemical experiments. The role of relativistic effects is discussed in detail. 

The discovery of new chemical elements— the transactinides or superheavy elements—stimulated the work on theoretical predictions of their chemical properties. Our intention is to present in Part II of this chapter empirical methods from [23-37] and from our partly unpublished work [38-50], which are used to predict chemical properties of elements and compounds relevant to gas-phase chemical studies of transactinides. 

Mendeleev had sufficient confidence in his periodic law to use it to predict the existence of several new elements, and the properties of their compounds, in addition to correcting the atomic weights of some already known elements. Nevertheless, this predictive aspect seems to have been overemphasized by historians of chemistry and writers of chemistry books. It appears that Mendeleev s ability to accommodate the already known elements may have contributed as much to the acceptance of the periodic system as did his dramatic predictions. For example, the citation which accompanies his being awarded the Davy Medal by the Royal Society of London makes no mention whatsoever of his predictions (Scerri 1996). 

This was a new fundamental discovery in thermodynamics, not demonstrable or predictable from previously known thermodynamic principles. It says that as we approach 0 K, the entropies of all known species (elements and compounds) approach the same value. It doesn t make much difference what that value is, as long as it is the same per mol of atoms, because the number of mols of atoms is conserved in any chemical reaction. The universally adopted convention is to make that value zero. (Other choices would have been correct, but would lead to much nastier mathematics.) This is called the third law of thermodynamics, stated formally as follows The entropy of any pure crystalline substance rzt 0 K is zero. The pure crystalline is explained below. The entropy based on this statement is called the absolute entropy, which means entropy relative to that of a pure crystalline substance at 0 K. It is not the same as steam table entropies, which are relative to an... 

The mineral petalite was mined as an ore in Sweden. In 1817 Johan August Arfwedson (1792—1841) analyTed this new mineral. After identifying several compounds in the ore, he realized there was a small percentage of the ore that could not be identified. After applying more analytical procedures, he determined it was a new alkali. It turned out that petalite contains hthium aluminum silicate, LiAllSi O lj. In 1818 the first lithium metal was prepared independently by two scientists, Sir Humphry Davy (1778—1892) and W.T. Brande (1788—1866). Lithium was discovered at a time in the early nineteenth century when numerous new elements were discovered and identified by other scientists. Many of these newly named elements were predicted by the use of the periodic table of the chemical elements. 

Even the development of Mendeleyev s periodic table of chemical elements did not grant researchers the ability to plan and design new materials. Although Mendeleyev correctly predicted the existence of a few new elements, the number of compounds that can be made from elements is extremely vast and complex. Chemical Abstracts Service, a division of the American Chemical Society, maintains a registry of known substances. As of May 2009, there are about 47 million substances in this registry, and roughly 4,000 new substances are added every day. 

Chemists and physicists have collaborated since the middle of the twentieth century to make new elements substances never before seen on Earth. They are expanding the Periodic Table, step by painful step, into uncharted realms where it becomes increasingly hard to predict which elements might form and how they might behave. This is the field of nuclear chemistry. Instead of shuffling elements into new combinations - molecules and compounds - as most chemists do, nuclear chemists are coercing subatomic particles (protons and neutrons) to combine in new liaisons within atomic nuclei. 

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