What substance the heaviest?
right at the beginning, it appears, are pertinent to make the reservation and to tell that in this article we will speak about pure substances, i.e. such substances which consist of atoms of one chemical element. Moreover, we should address Mendeleyev`s table to be convinced that it … is not finished.
This is true. In the advanced scientific laboratories scientists manage to receive atoms of elements which at the time of experiments are not brought in periodic table though the possibility of their existence is supposed the table if not to tell - it is proved. Filling of the table of Mendeleyev goes towards increase in atomic mass of the received elements, however a number of the additions made to it and changes cannot be infinite. We will consider the reasons of this phenomenon below.
It is known that atoms can be stable and unstable (the second, unlike the first, have small life expectancy and stop the existence through disintegration with formation of atoms of other elements or particles). Stability of an element is defined by a ratio of number of the protons and neutrons entering it (together called by nucleons). From elements known for today (including received in the artificial way) 94 meet in the nature. Each element in the nature can exist in the form of a set of isotopes, i.e. atoms which differ from each other in number of the neutrons entering them (and, therefore, in mass number), but contain identical number of protons (so, and electrons) which defines the provision of an element in periodic table and its chemical properties. Various isotopes of the same element possess different degree of the stability defining their susceptibility to disintegration.
From the elements which are found in the nature the heaviest among substances, solid under usual conditions, is osmium (Os, density - 22,59 g / cubic cm), among gases - radon (Rn, density - 0,01 g / cubic cm). However the elements synthesized in vitro often call superheavy. They exist only thousand fractions of a second, right there breaking up, but the fact that the found element existed and was noticed, is the cause for the announcement of its opening.
In scientific laboratories various methods of receiving superheavy elements are applied:
bombing of a kernel - a target of one element atoms of another (for example, California calcium); in this case the purpose is the greatest possible saturation of a kernel - a target neutrons; if it is possible to reach as a result of such bombing of one of magic numbers (about them - slightly lower), then thereby it is possible to present life to a new kernel with a weight exceeding the mass of kernels of each of the elements involved in process;
cold connection of difficult kernels (one of them at the same time disperses on the special accelerator up to the speed which only much is inferior to velocity of light);
nuclear explosions, etc. a job by the Russian scientists were got by
as a result of such elements with serial numbers 113, 114, 115, 116, 118 (the last element was received in 2003, it is officially recognized in 2006).
It is not as simple to prove the fact of receiving a new element as it seems at first sight. Among millions of disintegrations and transitions of one elements to others going in the difficult equipment to prove the existence of a new kernel lasting fractions of a second, difficult including for the reason that it is necessary to deal with probability of emergence during tests of a statistical error capable to cause “ as if “ fixing of a new element.
Generally speaking if to take such fact as stability into account, then superheavy-nuclei with increase in their weight (and numbers in Mendeleyev`s table) have to lose everything in bigger and bigger degree the stability. What then the scientists aspiring for certain not for the excess filled cell in periodic table hope for (or not only for this purpose) to synthesize the next element which is not opened hitherto?
It appears, the answer is simple: they count on a so-called structural barrier. It is peculiar to heavy-nuclei, and the essence it is reduced to a delay for some time an alpha - disintegration as a result of which this element will cease to exist. To assume existence of such barrier became possible by results of long-term experiments. The following thought is key here: superheavy-nuclei can be stable.
By the way, and what magic numbers which we mentioned earlier are? Answer: 2, 8, 20, 28, 50, 82 184 (is also (supposed). These numbers reflect quantity of the neutrons which most often are found in stable kernels. Hopes of scientists for synthesis of superheavy-nuclei which will be, as expected, stable are also pinned on the last of them. In this case it is accepted to speak about achievement “ islands of stability “ which existence scientists predict, but to reach it and furthermore still nobody could determine its sizes.
It is necessary to notice that the considerable mass of kernels of synthesizable elements affects their chemical properties which can from - behind this of weight to deviate predicted and to correct the law on frequency of chemical properties of elements formulated by Mendeleyev.
Thus, all new elements with the growing atomic mass allow us with healthy curiosity to watch scientific experiments on receiving this process and to postpone the answer to the question which is taken out in heading to later term.
What the century of opening prepares for us?.