[Chemistry Class Notes] on Periodic Table – Isotopes Element Pdf for Exam

Role Of Isotopes In Chemistry 

The first three Thorium, radiator, and ionio, of atomic number 90, were identified. Non-radioactive were instead discovered in 1914 by O. Hönigschmid, who found two of the lead. The term was introduced in 1913 by F. Soddy. Isotopes are atoms of the same element that have an equal number of protons but a different number of neutrons. The mass numbers are always indicated with A, while Z refers to the atomic numbers of the elements. The atomic number symbolizes the number of protons in the nucleus of an atom and is used to identify the position of the element on the periodic table. The mass number of an atom is the number of neutrons in its nucleus. The isotopes of the elements have different physical properties due to the variation in their atomic masses. Because of this difference, these isotopes have different densities, as well as melting and boiling points. However, the isotopes of an element always have very similar chemical properties. The similarity occurs because only electrons are used in chemical reactions, not in neutrons or protons.

Features

They can be stable or unstable (or radioactive), natural, i.e. existing in nature, or artificial, i.e. produced as a consequence of provoked nuclear reactions. The electronic structure is identical for all of the same elements; equal is the number of protons that form the nucleus of each. It is the atomic number; the number of neutrons is different (see e.g. in fig.) and therefore the mass number. Usually, it is indicated by proceeding the symbol of the chemical element by two numbers, of which one, at the bottom, is the atomic number, the other, at the top, is the mass number. Thus, the two stable carbons (atomic number 6 and mass number 12 and 13) are indicated by the symbols 126C and 136C, respectively.

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Isotopic Composition And Isotopic Number Of Elements

From a strictly physical point of view, a particularly interesting problem is that the isotopic composition of the elements is extremely varied. While some elements are more stable, others are very poor (e.g., fluorine does not have stability) due to the different stability of the various nuclides (nucleus). A picture of the situation (determined by nuclear forces) is provided by the following rules of thumb: a) the first Mattauch rule says that there are no stable isobars, that is, there is only one stable nuclide if the mass number A is odd; b) Mattauch’s second rule says that. if A is even, there are several stable isobars; elements that have only one stable nuclide, i.e. without stable, have odd mass number A and atomic number Z (except 34Be); if Z is even there are numerous  (the number of stable nuclides is ≥3); c). Aston’s rule, finally, says that if Z is odd, the element has at most stable (i.e. at most two stable nuclides). Based on these rules, it is possible, at least in broad terms, to provide for the constitution in buildings of any element.

Isotopic Separation

To separate various methods of the same element are used, based on the slight differences in chemical and physical properties mentioned above, or, where are reduced to the ion state, based on the different electrical and magnetic behavior deriving from the different specific charges. Among the isotopic separation methods, we will mention the gas phase diffusion, the thermal diffusion, the fractional distillation, the centrifugation, all methods in which are not ionized, as well as electrolysis and electromagnetic separation, in which, instead I am in an ionic state.

Isotopic Effect (Or Displacement)

In spectroscopy, due to the dependence of the frequency of radiation emitted by an atom from the mass of the atom itself, two of the same elements emit in the same transition two slightly different frequencies (the relative difference of the two frequencies is: / = (me / M2) M, where is the electronic mass, M the atomic mass of and M + M that of the other).

Use Of Isotopes

In biology, they are mainly used in investigations on the localization of some chemical compounds in given organs or tissues, or even in particular cells or parts of them, and in the study of the replacement of some chemical constituents of organisms. The technique consists in introducing into the organism, orally or by injection or otherwise, substances containing a certain percentage of one or more radioactive (marked elements); after a certain time, it is possible to proceed with the search and possibly with the measurement of which are found in a given organ or a given substance extracted from an organ. A particular application, very important for various historical and geological problems, is that of the 146C, which has a half-life of 5600 years, for the dating of organic finds.