Periodic Table of the Elements, created primarily by a Russian chemist, Dmitry Mendeleev (1834-1907), celebrated its 150th anniversary last year. Its importance as an organizing principle in chemistry is difficult to overestimate – all emerging chemists are familiar with it from the very beginning of their education.
Given the importance of the table, one could apologize for the assumption that the order of the elements is no longer in question. However, two scientists in Moscow, Russia, recently published a Suggestion for a New Order.
First, let’s see how the periodic table developed. By the end of the eighteenth century, chemists were clear about the difference between an element and a compound: the elements were chemically indistinguishable (eg, hydrogen and oxygen), but the compounds contained two or more elements that were completely different from the constituent elements.
It was there at the beginning of the nineteenth century. Good circumstantial evidence for the existence of atoms. By the 1860s, known elements could be listed in terms of their relative atomic mass – for example, hydrogen 1 and oxygen 16.
Simple lists are of course monotonous. Chemists knew that some elements had similar chemical properties: for example, lithium, sodium, potassium or chlorine, bromine and iodine.
Something seems to be repeating, and by superimposing chemically similar elements, a two-dimensional table can be constructed. The periodic table was born.
Importantly, Mendeleev’s periodic table was empirically based on the observed chemical similarities of certain elements. Until the early twentieth century, after the structure of the atom was established, with the development of quantum theory, a theoretical understanding of its structure would emerge.
The elements are arranged by atomic number (the number of positively charged particles called protons in the atomic nucleus) instead of atomic mass, but are still chemically similar.
The latter, however, at regular intervals follow the arrangement of electrons called “shells”. By the 1940s, most textbooks contained a journal, as we see today, as shown in the image below.
Today’s periodic table. (Ofnopt / Wikipedia)
Understandably, this would be the end of the matter. However, this is not the case. A simple internet search will reveal all kinds of versions of the periodic table.
There are short versions, longer versions, round versions, spiral versions and 3D versions. Many of these are different ways of transmitting the same information, but disagreements remain over where to place certain elements.
The exact location of certain elements depends on the specific features we want to highlight. Therefore, a periodic table that emphasizes the electronic structure of atoms will differ from tables of important chemical or physical properties.
These versions are not very different, but there are some elements – hydrogen, for example – that can be placed completely differently depending on the specific property you want to emphasize. Some tables place hydrogen in group 1, while others sit above group 17; It’s even on some tables in its own group.
More radically, however, the arrangement of the elements can be considered in a completely different way, which does not contain atomic numbers or reflect the electronic structure – reversing to a dimensional list.
New proposal
The latest attempt to arrange the elements in this way Recently published Journal of Physical Chemistry Scientists Saheed Alhari and Artem Oganov.
(Alhari et al., Journal of Physical Chemistry, 2020)
Their approach, based on the previous work of others, is to assign a Mendeleev number (MN) to each part.
There are several ways to obtain such numbers, but the latest study uses a combination of two basic quantities that can be measured directly: the atomic distance of an element and a property. Electro-negativity This explains why an atom attracts electrons.
If you order their parts from their MN, let the neighbors surprise you, they have a similar MN. But for further use, it goes one step further and builds a two-dimensional grid based on the MN of the so-called “binary connections”.
These are compounds consisting of two components, sodium chloride and NaCl.
What is the advantage of this approach? Importantly, it can help predict the characteristics of binary connections that have not yet been manufactured. It is useful in the search for new materials needed for future and current technologies. Over time this will spread to compounds with two elementary components.
Given the periodic table shown in the figure below, a good example of the importance of looking for new materials can be appreciated.
Periodic table with the relative abundance of elements. (European Chemical Society / Wikipedia / CC BY-SA)
This list highlights not only the relative abundance of elements (each component has a bigger box, there are more of them), but also the distribution issues relevant to technologies that have become ubiquitous and indispensable in our daily life.
Take cell phones, for example. All the components used in manufacturing are identified with the phone icon, and you can see that many of the required components are in short supply – their future distribution is uncertain.
If we develop substitute materials that avoid the use of particular components, the insights gained from ordering the components can be valuable in that quest.
150 years later, magazines are not only an important educational resource, but they also continue to be useful to researchers in the search for essential new material. We don’t have to come up with new versions to replace the previous illustration. Having different lists and lists helps us better understand how components work.
Nick Norman, Professor of Chemistry, University of Bristol.
This article has been republished Conversation Under the Creative Commons License. Read the original article.
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