the isoelectronic series
At least two atoms, ions or molecules are called isoelectronic, if they have the same number of electrons and a very similar electron configuration. Never the less they may consist different elements. The isoelectronic rows which are considered in this essay are defined by the elements and their ionized states.
During the ionization of the elements, again and again similar electron configurations arise. For example, the electron configuration of He+ is in principle identical to that of hydrogen. Another example are Li+ and He; of curse the nucleus vary regarding the amount of protons. This similar behavior of the ionization is used to form the isoelectronic series. Each examined series starts with the energy of ionization of the neutral element and is carried forward by the next higher element that is single-ionized . This process is transferred regarding all known elements. Mrs. Lisitzin has enforced her investigations until 1936. At that moment, not all the ionization energies of the elements were measured reliably; some elements weren’t measured at all. Therefore Mrs. Lisitzin could not develop and investigate isoelectronic series for all elements and their ionisation stages. For the elements of the transition periods 6 (lanthanoids) and 7 (actinides), there wasn’t any data available at all.
The first isoelectronic series contains all elements of the periodic table. The first link in the chain is the hydrogen atom, the second is the singly ionized helium atom, the third is the two times ionized lithium; each member of the series only has one electron.
This series then continues until the last known element.
The second row starts with the energy of the ionization of neutral helium. This series also ends with the last known element. Each member of this series has two electrons. These series continue until the last known element, which forms the series with no more members than itself.
The integration of affinity energy into the isoelectronic series is not considered in this work. As shown by Mrs. Lisitzin, these isoelectronic series of ionization energies can be approximated by polynomials of the second degree.
Since E_in is calculated in electron volts (eV), the right side of the equation, of course, has to be shown in electron volts as well. The atomic number has no dimension but is a pure number that expresses the number of protons of the elements. Regarding the coefficients that means that the following units can be allocated:
In the figure (Fig.: 1) below, the approaches of the isoelectronic series of the elements are shown. The illustrated isoelectronic series were formed by the measured values of the ionization energy of the elements. I used all published data regarding ionization energies of the elements that were available. This figure doesn’t show the polynomials which were developed by Mrs. Lisitzin but the measured ionization energies.
A striking feature of this isoelectric series are the occurring regularities and their structural order. Hereinafter, these structures are analyzed and interpreted by means of Eugenie Lisitzin’s work.