Relearning the Periodic Table: Some History

Last week, the names of four elements were officially accepted by the International Union of Pure and Applied Chemistry (IUPAC). These elements were successfully synthesized several years ago, but they were accepted only last year, and their official names were yet to be decided until now. The elements, Nihonium (Nh), Moscovium (Mc), Tennessine (Ts) and Oganesson (Os) were the last four elements of the seventh row of the periodic table to be added, thereby “completing” the periodic table.

I cannot describe the satisfaction that, as a Chemistry enthusiast, I feel when I finally see the periodic table without any “holes” in it. Let me show you some pictures of some periodic tables to illustrate this point:

oldperiodictable

Periodic Table found in the book “Chemical Principles” (Masterton, Slowinski, Stanitski. Spanish version), printed in 1987. Five elements beyond Lawrencium (103) are shown with a section sign indicating that there were no official names for those elements at the moment.

highschoolperiodictable

This is the periodic table I used in high school and I believe I bought it almost 8 years ago. We can see that now all the blocks in the seventh row have something written on them, although from the element 110 on these are just the temporary names suggested by the IUPAC. Although some of those elements had been officially recognized and named by that time, it isn’t uncommon to see outdated periodic tables being sold in bookstores in El Salvador.

iupac_periodic_table-28nov16

This is the official periodic table on the IUPAC website. All the elements have a name and symbol now. (Unless, of course, we discover elements in lower rows).

Simply put, today’s Chemists grew up seeing an “incomplete” periodic table, and this is an amazing moment to be alive for many of us. For non-chemists, this raises many questions, such as: “is the periodic table really ‘complete’ or will more elements be discovered?” or “why is the periodic table organized the way it is?.” Another question that you might be asking yourself right now is “why did I have to memorize this at school?” which, even as a chemistry major, is something I don’t understand either, since I never needed to memorize past the third row myself. In any case, with the “completion” of the periodic table, I believe it’s a perfect time to relearn a little bit about the periodic table.

Some History

Several elements were well known since ancient times (gold, silver, iron, etc.) but the first recorded discovery of an element was in 1669, when Hennig Brand isolated phosphorus. At the time, however, there was no clear definition of what elements and compounds were (there were just many philosophical theories). In 1789, Antoine Lavoisier was the first person to make a list of 33 chemical elements which, in fact, included some compounds and two other interesting “substances”: heat (calorique) and light (lumière). Back then, chemists had no deterministic way of telling whether something was an element or a compound. This was usually done by studying their chemical properties, using reaction stoichiometry, in order to determine the molecular weights of different substances, and trying to understand which were the building blocks that couldn’t be separated into more elemental parts. Later on, different methods such as spectroscopy were used to identify new elements. Around the beginning of the 20th century, our understanding of atoms became sophisticated enough for us to understand what makes an element an element, so we can now just say “if it’s on the periodic table, it’s an element.”

lavosier

Lavoisier’s Elements

The development of the periodic table, however, anticipated the discovery of electrons and atomic nuclei. Without the understanding that elements differ from each other because of the number of protons in their nuclei, many chemists tried to find a way to organize the elements during the 19th century. Some chemists noticed that if we make a list of the elements based on their atomic weights some properties tend to repeat. This is what we call periodicity nowadays. In 1864, John Newlands suggested that these properties repeat every eight elements, just like with octave in music. Since many elements hadn’t been discovered, there were many flaws in his theory, and when he presented it at the Chemical Society (London), nobody was particularly impressed and they decided not to publish his work. Many Chemistry textbooks include the rumor that someone even asked him to try writing them in alphabetical order and see if he could find something. It would take another five years for a Russian scientist to come up with a better theory of periodicity.

800px-dimendeleevcab

Although the history of Chemistry includes many important figures, I believe that every basic Chemistry course in the world devotes at least some minutes to the story of Dmitri Mendeleev. Some people say that he would sometimes isolate himself from people and just think for several days. Others say that he would play some solitaire-like game with cards representing the elements and their facts. Regardless of how he tackled the problem, he eventually came up with a table of the elements in a dream, according to his diary. The elements were arranged based on their atomic weights (he never knew about Newlands’ work) and every row consisted of elements with similar chemical and physical properties. The innovative part of his work (and the amazing part of the story that blows everyone’s mind) was that he studied so many properties and generated so many patterns that he was confident enough to leave empty spaces for elements that hadn’t been discovered yet, and he even predicted—quite accurately—their properties. I recommend you to watch this video by TED-Ed about it. Nowadays many people call him “the Father of the Periodic Table,” and in many countries (especially in many Slavic countries) the periodic table is called “Mendeleev’s table” (Таблица Менделеева in Russian).

mendelejevs_periodiska_system_1871

Mendeleev’s Periodic Table (The elements with an atomic weight but represented only with a dash represent predicted elements).

After Mendeleev’s periodic table, periodicity became a standard concept in Chemistry, and that paved the way to a greater understanding of the elements. But how does periodicity work? Find out in our future entries! You can subscribe to this blog by clicking the “follow” button on the top right corner (or below if you’re using a smartphone), or you can also follow The Relearner on Facebook, Twitter, and Instagram to see our latest posts right on your news feed. The Relearner works for you and also thanks to you, so please check the Support Us section of our blog. Share this entry on Facebook, Twitter or Instagram with the hashtag #TheRelearner and tell us your favorite element, and you’ll have the chance to get a souvenir from Nagoya University. A winner will be chosen every month. Thank you and see you next time!


Gerardo Urbina is a Chemistry student at Nagoya University who loves reading and learning about anything. Born and raised in El Salvador, he speaks Spanish, English and Japanese and is currently learning French and Russian. Read more about him and his ideas for The Relearner.

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