Periodic table of elements, prepared mainly by Russian chemists, Dmitry Mendeleev (1834-1907), celebrated it 150th Anniversary last year. It would be difficult to overstate its importance as an administrative theory of chemistry – all emerging chemists become familiar with it from the earliest stages of their education.
Given the importance of the table, one can be forgiven for thinking that the order of the elements is no longer the subject of debate. However, two scientists in Moscow, Russia, have recently published one Proposal for new order.
Let us first consider how the periodic table was developed. By 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 element Are.
In the early 19th century, c Evidence of good conditions For the existence of atoms. And by the 1860s, it was possible to list known elements according to their respective atomic masses – for example, hydrogen 1 and oxygen 16 c.
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 be repeated, and by placing chemically identical elements in front of each other, a two-dimensional table could be created. The period table 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.
Elements were now validated by atomic number (the number of positively charged particles called protons in the atomic nucleus), not by atomic mass, but still by chemical similarities.
But the latter now comes after managing electrons at regular intervals, repeating in so-called “shells”. Until the 1940’s, most textbooks had a periodic table as we see it today, as shown in the figure below.
Today’s Periodic Table (Offnopopt / Wikipedia)
It makes sense to think that this would be the end of the matter. No, but. A simple search of the internet will come up All kinds of versions Of periodic table.
There are short versions, long versions, circular versions, spiral versions and even three-dimensional versions. Many of them, of course, have different ways of conveying the same information but some disagree about where the elements should be placed.
The exact placement of some elements depends on what features we want to highlight. Thus, a regular table that prioritizes 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 sit at the top of group 17; Some tables also have it In a group in itself.
In addition, more indirectly, we may consider ordering elements in a very different order, one that does not contain atomic numbers or represent an electronic structure – returning to a one-dimensional list.
New proposal
The latest attempt to order elements in 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 first work of others, To determine each element called the Mendeleev number (MN).
There are many ways to calculate such numbers, but the latest study uses a combination of two basic quantities that can be measured directly: the atomic circumference of an element and an property called. Electronegativity Which shows how strongly an atom attracts electrons.
If one orders the elements through their MN, the nearest neighbors, instead of being surprised, have the same MN. But the most common use is to take it a step further and build a two-dimensional grid based on the MN 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 in finding new content that is potentially needed for both 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 time table 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 elements (as large as the box of each element) but also highlights the potential supply issues related to the most widespread and essential technologies in our daily lives.
Take mobile phones, for example. All the elements used in their manufacture are identified by the phone icon and you can see that many required elements are missing – their future supply is unclear.
If we are to develop alternative content that avoids the use of certain elements, the insights gained by their MN through elementary elements may prove important in this research.
150 years later, we can see that from time to time tables are not only an important educational tool, they remain useful in the search for new materials necessary for researchers. But we should not think of new versions as a replacement for 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 has been republished Conversation Under the Creative Commons license. Read them Original article.
