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The periodic table of the elements, prepared mainly by Russian chemists Dmitry Mendeleev (1834-1907), celebrated it last year’s 150th anniversary. It would be difficult to overstate its importance as an administrative theory of chemistry: all emerging chemists know it from the earliest stages of their education.
Given the importance of the table, it can be forgiven for thinking that the order of the elements is no longer the subject of debate. However, two scientists in Moscow, Russia recently published a Proposal for a New Order.
Let’s first consider how the periodic table was developed. At the end of the 18th century, chemists were clear about the difference between an element and a mixture: the elements were chemically indivisible (e.g. hydrogen, oxygen) while the mixture contained two or more elements, different from the Are element.
At the beginning of the 19th century, c Proof of good conditions for the existence of atoms. And in the 1860s it was possible to list the known elements based on their respective atomic masses, for example hydrogen 1 and oxygen 16c.
Simple lists, of course, are one-dimensional in nature. But chemists knew that some elements had the same chemical properties instead: for example lithium, sodium and potassium or chlorine, bromine and iodine.
Something like this seemed to repeat itself, and by placing chemically identical elements facing each other, a two-dimensional table could be created. The table of the period was born.
Importantly, Mendeleev’s periodic table was enthusiastically obtained based on the observed chemical similarities of certain elements. This will not happen until the beginning of the 20th century, when the atomic structure is established and the development of quantum theory, the theoretical understanding of its structure will emerge.
The elements were now validated by atomic number (the number of positively charged particles called protons in the atomic nucleus), not by atomic mass, but again by chemical similarities.
But the latter now comes after managing the electrons at regular intervals, repeated in the so-called “shells”. Until the 1940s, most textbooks had a periodic table as we see it today, as shown in the following figure.
Periodic Table Today (Offnopopt / Wikipedia)
It makes sense to think that this would be the end of the matter. No but. A simple search on the Internet will appear All kinds of versions of the periodic table.
There are short versions, long versions, circular versions, spiral versions and even three-dimensional versions. Many of them obviously have different ways of conveying the same information, but some disagree on where the elements should be placed.
The exact positioning of some elements depends on the characteristics we want to highlight. Therefore, a regular table that gives priority to the electronic structure of atoms differs from tables in that the main criteria are certain chemical or physical properties.
These versions are not very different, but there are some special elements – for example hydrogen – that can be differentiated according to the particular property that the person wants to cultivate. Some tables contain hydrogen in group 1, while others are found at the beginning of group 17; Some tables even have it in a group itself.
Also, more indirectly, we can consider sorting the elements in a very different order, one that does not contain atomic numbers or represents an electronic structure, returning to a one-dimensional list.
New proposal
The latest attempt to sort items this way was recently published Journal of Physical Chemistry By scientists Zahid Allahhari and Artem Oganov.
(Al-Hayari et al., Journal of Physical Chemistry, 2020)
Their Approach Building on the early work of others, To determine each element called Mendeleev’s number (MN).
There are many ways to calculate such numbers, but the latest study uses a combination of two basic quantities that can be directly measured: the atomic circumference of an element and a property called. Electronegativity Which shows the force with which an atom attracts electrons.
If you sort items by their MN, the closest neighbors, instead of being surprised, have the same MN. But the most common use is to go a step further and build a two-dimensional grid based on the NM of the partial elements in the so-called “binary mixture”.
These are compounds made up of two elements, such as sodium chloride, NACL.
What is the benefit of this approach? Importantly, it can help predict the properties of binary compounds that have not yet been developed. This is useful for finding new content potentially needed for future and current technologies. Over time, no doubt, it will grow into compounds with more than two elementary components.
A good example of the importance of finding new content can be appreciated by considering the timetable shown in the figure below.
The periodic table represents the appropriate abundance of elements. (European Chemical Society / Wikipedia / CC BY-SA)
This table not only shows the abundance of items (as big as the box of each item) but also highlights the potential procurement issues related to the most widespread and essential technologies in our daily life.
Take cell phones, for example. All items used in their manufacture are identified by the phone icon and you can see that many required items are missing – their future supply is unclear.
If we want to develop alternative contents that avoid the use of certain elements, the insights acquired by their MN through elementary elements can prove important in this research.
150 years later, we can see that from time to time tables are not just an important educational tool, they remain useful in finding new materials that researchers need. But we shouldn’t think of the new versions as a replacement for the old images. Having so many different tables and lists gives us an in-depth understanding of how the elements behave.
Nick Norman, Professor of Chemistry, University of Bristol.
This article was republished Conversation under the Creative Commons license. Read them Original article.
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