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The chronology of the elements, mainly developed by a Russian chemist, Dmitry Mendeleev (1834-1907), celebrated 150th Anniversary Last year. It is difficult to overstate its importance as an organizing principle in chemistry – all emerging chemists are familiar with it from the earliest stages of their education.
Given the importance of the table, one can be excused for thinking that the ordering of the elements is no longer subject to discussion. However, two scientists in Moscow, Russia, recently published one Plan for new order.
Let us first consider how the timetable was created. In the late 18th century, chemists were clear about the difference between an element and a compound: the elements are chemically indistinguishable (e.g. hydrogen, oxygen), while compounds combine two or more components and have completely 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 known components in the order of their relative atomic masses – for example, hydrogen 1 and oxygen 16.
Simple lists are, of course, an experiment 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 each other, a two-dimensional table could be created. The timetable was born.
Importantly, Mendeleev’s timeline was empirically derived based on the observed chemical similarity of some components. Until the early 20th century, the structure of the atom was established and, following the development of quantum theory, a theoretical understanding of its structure would emerge.
The elements are now sorted not by atomic mass but by atomic number (the number of positively charged particles called protons in the nucleus), but still by chemical similarity.
But the latter is followed by the arrangement of repeated electrons at regular intervals in what are now called “shells”. In the 1940s, most textbooks featured a timetable similar to the one we see today, as shown in the picture 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. An easy search of the internet will reveal All kinds of versions Of the schedule.
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 certain elements depends on what specific properties we want to highlight. Therefore, a timeline that gives priority to the electronic structure of atoms may differ from tables that have certain chemical or physical properties on key criteria.
These versions do not differ greatly, but there are some components – for example hydrogen – which can be placed very differently depending on the specific property you want to highlight. Some tables put hydrogen in group 1, while others sit at the top of group 17; Some tables even have it Its own in a group.
However, more seriously, we can also consider sorting the elements in a very different way, which does not include the atomic number or the electronic structure – converting it to a one-dimensional list.
New project
The latest attempt to order components in this manner Recently Published Journal of Physical Chemistry By scientists Zaket Allahari And Artem Okanov.
(Allahari et al., Journal of Physical Chemistry, 2020)
Their attitude, Creating others ’previous work, Each element is called the Mendeleev number (MN).
There are many ways to get such numbers, but a recent study uses a combination of two basic quantities that can be measured directly: the atomic radius of an element and a property. Electronectivity It describes how strongly an atom attracts electrons.
If one orders elements through their MN, the nearby neighbors will be surprised to find similar MNs. But what is more useful is to take this one 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 advantage of this approach? Importantly, it helps to predict the properties of binary compounds that have not yet been done. This will be useful in the search for new products needed for future and existing technologies. Over time, this will no doubt extend to compounds with two basic components.
A great example of the importance of looking for new items can be appreciated considering the timeline shown in the image below.
Schedule showing the relative abundance of elements. (European Chemical Society / Wikipedia / CC BY-SA)
This table illustrates the relative abundance of elements (the larger the box for each element, the more it contains) but also highlights the potential distribution problems associated with technologies that have become ubiquitous and essential in our daily lives.
Take mobile phones, for example. All the components used in their production are identified with 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 intelligence gained by sorting the elements by their MN will be valuable in that search.
150 years later, schedules are not only an important educational tool but also useful for researchers in the search for essential new items. But we should not 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 has been republished Conversation Under the Creative Commons license. To read Original article.
