The periodic table of elements originally created by the Russian chemist Dmitry Mendeleev (1834-1907) celebrates its 150th anniversary last year. It is difficult to overestimate the importance of chemistry as an organizational principle – all emerging chemists are familiar with it from the very beginning of their education.
Considering the importance of tables, one can be forgiven for thinking that the order of the elements is no longer a matter of debate. But two Russian scientists in Moscow have recently proposed a new order.
Let us first consider how the periodic table was developed. By the end of the eighteenth century, chemists were clear about the difference between an element and a compound: the elements were chemically indivisible (e.g. hydrogen, oxygen) where the compound consisted of two or more combinations, the properties of which differed from the elements.
In the early nineteenth century, there was good circumstantial evidence for the existence of atoms. And by the 1860s, it was possible to list known elements according to their relative atomic mass – for example, hydrogen 1 and oxygen 16.
The general list is of course one-dimensional in nature. Chemists, however, were aware that certain ingredients had similar chemical properties instead: for example lithium, sodium and potassium or chlorine, bromine and iodine.
Some seem to be repetitive and by placing chemically similar elements next to each other, a two-dimensional table can be created. The periodic table was born.
Importantly, Mendeleev’s periodic table was experimentally generated based on the observed chemical similarities of certain elements. Once the structure of the atom is established and the development of quantum theory, it should not be at the beginning of the twentieth century, a theoretical understanding of its structure will emerge.
The elements were ordered by atomic number (number of positively charged particles called protons in the atomic nucleus) by atomic number, but still by chemical match.
Subsequent actions, however, follow the management of the repeated electrons in the so-called “shells” at regular intervals. In the 1940s, most textbooks featured a periodic table as we see it today, as shown in the figure below.
It is to be thought that this matter will end. But it is not. A simple search on the Internet will reveal all sorts of versions of the periodic table.
There are short version, long version, circular version, spiral version and three-dimensional version. Many of them are convinced that the only way to convey the same information is to continue to disagree on where to place certain elements.
The exact position of certain elements is determined depending on which particular features we want to highlight. Thus, periodic tables that predominate the electronic structure of atoms will differ from those for which the main criteria are specific chemical or physical properties.
These versions are not very different, but there are some elements – hydrogen, for example – that can set one apart according to the particular property it wants to highlight. Some tables place hydrogen in group 1 while it sits at the top of group 17; Some tables even have it in their own group.
Rather more radically, however, we can also consider ordering elements in very different ways, which do not involve atomic numbers or reflect electronic structures – return to one-sided dimensions.
The latest attempt to order components in this manner was recently published Journal of Physical Chemistry Scientists Jahed Allahiari and Artem Oganov.
Their point of view based on the previous work of others is that each element is called a Mendeleev number (MN).
There are different ways to obtain such numbers, but the latest study uses a combination of two basic quantities that can be measured directly: an atomic radius of an element and a property called electromotivity that describes how an atom attracts electrons.
If someone orders the ingredients by their MN, it is not surprising to the nearest neighbors, but there are similar MNs. Further use, however, is to take this one step further and create a two-dimensional grid based on the MN of the constituent elements in the so-called “binary compounds”.
These are compounds made up of two components, such as sodium chloride, NKL.
What are the advantages of this method? Importantly, it can help predict the properties of binary compounds that have not yet been created. It is useful in the search for new materials that are necessary for both the future and existing technology. In time, no doubt, it will expand into compounds with more than two basic elements.
A good example of the importance of finding new materials can be appreciated by considering the periodic table in the figure below.
This table not only illustrates the relative abundance of components (larger box for each component, the greater the amount) but also highlights potential supply issues related to the technology that has become ubiquitous and essential in our daily lives.
Take mobile phones, for example. All the components used to make them can be identified by phone icons and you can see that a number of essential components are becoming scarce – their future supply is uncertain.
If we can create replacement materials that avoid the use of specific components, the insights gained by ordering components by their MN can prove valuable in that search.
150 years later, we see that periodic tables are not only an important educational tool, they are useful for researchers in finding the necessary new materials. But we should not think of new versions as a replacement for previous versions. Having different tables and lists only deepens our understanding of how elements behave.
Dr. Nick Norman, Professor of Chemistry, University of Bristol.
This article has been republished from the conversation under the Creative Commons license. Read the original article.
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