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The chronology of the elements, developed mainly by a Russian chemist, Dmitry Mendeleev (1834-1907), celebrated its 150th anniversary last year. It is difficult to overestimate its importance as an organizing principle in chemistry: all emerging chemists know it from the earliest stages of their education.
Given the importance of the table, one can be excused for thinking that the order of the elements is no longer subject to discussion. However, two scientists in Moscow, Russia recently published a Plan for the New Order.
Let’s first consider how the calendar was created. At the end of the 18th century, chemists were clear about the difference between an element and a compound: elements are chemically indistinguishable (e.g. hydrogen, oxygen), while compounds have two or more components that have different properties from their constituents.
In the early 19th century, there was good circumstantial evidence for the existence of atoms. In the 1860s it was possible to list the known components in the order of their relative atomic masses, for example hydrogen 1 and oxygen 16.
Simple lists are, of course, one dimension in nature. But chemists knew that some elements had similar chemical properties: for example, lithium, sodium and potassium or chlorine, bromine and iodine.
Something reappeared and by placing chemically identical elements on top of each other, a two-dimensional table was created. The timetable was born.
Importantly, Mendeleev’s chronology was derived empirically based on the observed chemical similarity of some components. Until the beginning of the 20th century, the structure of the atom was established, and following the development of quantum theory, a theoretical understanding of its structure emerged.
The elements were now sorted not by atomic mass but by atomic number (the number of positively charged particles called protons in the nucleus), but again by chemical similarities.
But the latter is followed by the arrangement of electrons repeated at regular intervals in what are now called “shells”. In the 1940s, most textbooks featured a timetable similar to what we see today, as shown in the image below.
Today’s timetable. (Offnfopt / Wikipedia)
It would be understandable to think that this would be the end of the matter. However, this is not the case. A simple search on the Internet will reveal all sorts of versions of the program.
There are short versions, long versions, circular versions, spiral versions and even three-dimensional versions. Many of these are different ways of expressing the same information, but there are constant differences of opinion as to where certain elements should be placed.
The exact location of some elements depends on what specific properties we want to highlight. Therefore, a primary timeline for the electronic structure of atoms differs from the table in that the main criteria for it are certain chemical or physical properties.
These versions don’t differ much, but there are some components – hydrogen for example – that can be placed very differently depending on the specific property you want to highlight. Some tables place hydrogen in group 1, while others sit on top of group 17; Some tables even have it in a group.
However, more seriously, we can also consider ordering the elements in a very different way, which does not include the atomic number or the electronic structure, by converting it into a one-dimensional list.
New project
Last attempt to order components this way Recently Released Journal of Physical Chemistry By scientists Zaket Allahari and Artem Okanov.
(Allahari et al., Journal of Physical Chemistry, 2020)
Their attitude, creating the previous work of others, Each element is called Mendeleev number (MN).
There are many ways to obtain such numbers, but recent research uses a combination of two basic quantities that can be directly measured: the atomic radius of an element and an Electronectivity property.It describes the force with which an atom attracts electrons.
If you order items via their MN, the neighboring neighbors will be surprised to find similar MNs. But what’s more useful is to go a step further and create a two-dimensional phase based on the MN of block components called “binary compounds”.
These are two component compounds such as sodium chloride and NaCl.
What is the benefit of this approach? Importantly, it helps predict the properties of binary compounds that have not yet been made. This will be useful in finding new products needed for future and existing technologies. Over time, this will undoubtedly extend to compounds with two basic components.
A great example of the importance of finding new articles can be appreciated by considering the timeline shown in the image below.
Program showing the relative abundance of elements. (European Chemical Society / Wikipedia / CC BY-SA)
This table illustrates the relative abundance of elements (big box for each element, there are many more) but also highlights the potential distribution problems associated with technologies that are ubiquitous and essential in our daily life.
Take cell phones, for example. All components used in their manufacture are identified by the phone icon and you can see that many of the required components are in short supply – their future supply is uncertain.
If we want to create alternatives that avoid the use of certain elements, the insights gained by ordering the elements according to their MN will be invaluable in that research.
150 years later, timetables are not only an important educational tool but also useful for researchers in their search for new essentials. But we shouldn’t think of new versions as an alternative to previous versions. Having many different tables and lists can help deepen our understanding of how elements work.
Nick Norman, Professor of Chemistry, University of Bristol.
This article was republished Conversation under the Creative Commons license. Read the original article.
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