In chemistry class, one of the first things that students are taught is that the elements are the building blocks of every existing matter in this world. Given the importance of elements, chemistry teachers use the lesson as a way to introduce the significance of the periodic table of elements and why it should be learned by all students. However, not all teachers tell students the story behind how the periodic table of elements came to be. This essay will talk about the history of the periodic table of elements and its creator, Dmitri Mendeleev.
What is the periodic table of elements?
The periodic table of elements is comprised of all the 118 chemical elements known to man. It arranges those elements in an informative way that can be easily understood even by laymen, or in most cases, students. The periodic table of elements gave chemistry a chance to be easily understood by young minds and keep them interested. But because most good teachers stimulate students to memorize the 118 elements found in the periodic table as a way to learn, students find themselves in need of tips to enhance their memory.
The periodic table of elements shows all the elements’ atomic weight, atomic number, electron configuration, and its chemical properties. In the periodic table of elements, the elements have been arranged according to their atomic number and grouped into non-metals, metals, and metalloids. Some elements found in the periodic table of elements have been discovered way before the beginnings of the modern atomic theory while some have just been discovered some five years ago.
In chemistry, an element is a substance that is made up of the same kind of atoms. All elements cannot be broken down into smaller substances but they can be combined to be transformed into other – or in some cases, new – elements by using nuclear procedures. All the atoms present in an element bear the same atomic number and when the number of protons in those atoms have changed, then the element changes along with it.
Knowing the periodic table by heart is probably one of the most difficult science assignments involving memory that a student has to go through. The periodic table of elements is probably the most recognizable illustration used in the study of science, particularly, in chemistry. More than 150 years after the periodic table of elements was first created, 55 elements have been added to the table as scientists keep discovering something new.
Of the 118 known elements, 98 of them occur naturally – meaning those need not be chemically engineered in laboratories. The remaining 20 elements needed laboratories and nuclear accelerators to be produced. 32 out of the 98 naturally-occurring elements are in their pure form while the remaining 66 are compounds. 80 naturally-occurring elements cannot be subjected to radioactive decay and is therefore considered stable.
History of the Creation of the Periodic Table of Elements
A number of scientists have tried to develop a comprehensive system of arranging all the known elements to man. Before the periodic table of elements was created, there was no way of explaining nor easily telling the relationships between the elements. Because of that, scientists began thinking of ways to identify and classify all discovered elements.
In the early 1800s, when English scientist John Dalton, he realized that what distinguished an atom of one element from an atom of another was its weight. Soon after Dalton published his atomic theory, Italian chemist Amadeo Avogadro showed that it made sense to suppose that a fixed volume of gas, whatever its chemical constitution may be, always contained the same number of particles, atoms, or molecules. This was Avogadro’s hypothesis. It was largely ignored at the time, but it became very important 50 years later.
A few years later, Swedish chemist Jöns Jacob Berzelius became the first scientist to make a systematic investigation of relative atomic weights. He published a list of weights, based on two standards; by giving hydrogen a weight of 1, and oxygen a weight of 100. There were some errors in the list. Berzelius identified some compounds as elements, but the idea that the atoms of elements differed from one another in atomic weight took a firm hold among chemists.
Less than a decade after, German chemist Johann Döbereiner posed that the known elements at the time may be grouped into three according to their similarities. What Döbereiner noticed is that is the three elements were arranged according to the number of their atomic weights, then the properties of each element also coincides with their position in the triad. Additionally, he observed that the average atomic weight of the first and third elements in the triad came close to the atomic weight of the second element in the triad. Döbereiner’s contribution managed to encourage chemists to observe the correlation between the elements’ atomic weights and their chemical properties.
One of the scientists Döbereiner influenced with his observations was Peter Kremers of Cologne who after researching the matter himself, found that it is possible for some elements to belong in two triads that are placed perpendicularly. This means that he analyzed and compared the elements from two directions – horizontally and vertically. This observation then became an essential part of the periodic table of elements known today.
By 1857, Jean-Baptiste- André Dumas, a French chemist, devised a set of mathematical equations to be used for accounting for the increase in weight of elements that are chemically similar. Of course, this attempt on creating a periodic table of element has failed because the atomic weight of an element is not a fundamental property that can be used to characterize an element.
Half a decade later, a French geologist by the name of Alexandre- Emile Béguyer de Chancourtois arranged the elements based on their atomic weights in which a periodicity in the properties of the elements have been observed. A rather complicated system was to be done in order to observe how similar properties of the elements can be observed and aside from that, the similarities are not convincing enough. Furthermore, he failed to include a diagram of the table in his original article which is mostly why the system he devised did not affect the scientists back then that much.
In 1864, English chemist John Newlands coined the law of octaves which is an observation of how any element – as long as the elements are arranged according to their atomic weight – showed similar properties to the elements eight places behind and ahead of a certain element. As with the periodic table of elements known today, Newlands placed blanks on the table he devised to make space for elements that are yet to be discovered. However, he did not include those blanks in the publicized version of the table which raised the objections of chemists because the table could not accommodate new elements.
Because of that, in 1866, George Carey Foster of University College London asked Newlands during a meeting of the Chemical Society in London whether he had considered ordering the elements alphabetically as this kind of arrangement often gives surprising coincidences. Because of this comment, chemists refused to publish Newlands’ paper.
Two years later in 1868, Julius Lothar Meyer of Breslau University, German chemist, managed to produce a periodic table of elements that is similar to the periodic table of elements that is being used today. Although, he did fail to correctly classify the elements in his periodic table. Aside from that, his periodic table of elements had not been published in 1870 – a year after the known periodic table of elements first appeared in print. This caused dispute between him and Dmitri Mendeleev, the creator of the periodic table of elements.
Who was Dmitri Mendeleev?
The periodic table of elements being used by students, academics, and chemists alike up to this day was developed by Dmitry Ivanovich Mendeleyev, better known as Dmitri, back in 1869. The periodic table of elements he created classifies the elements according to their chemical properties and increasing atomic weight. The atomic number, which identifies an element s position in the periodic table, is equal to the amount of protons in the nucleus.
Dmitri Mendeleev was a Russian chemist, best known for his development of the periodic law of the properties of the chemical elements. This law states that elements show a periodicity of chemical properties when the y are arranged according to atomic weight.
Dmitri Mendeleev was born in Siberia. He studied chemistry at the University of Saint Petersburg, where he got his master’s degree. Then he began conducting his research on organic chemistry. In 1859, he was financed by a government fellowship to study at the University of Heidelberg. There he met the Italian chemist Stanislao Cannizzaro, whose views on atomic weight influenced his thinking.
Upon returning from an international chemistry conference in Germany, Dmitri Mendeleev felt more passionate about chemistry. The conference was mainly focused on how chemistry needs to be standardized because at the time, they were only using symbols to represent the elements, but there is no universal illustration like the periodic table of elements. Mendeleev also observed that Russia may be falling behind Germany in regards to chemistry, and so he was determined to write a chemistry textbook.
He managed to publish his 500-page chemistry textbook, Organic Chemistry which took only 61 days to write. After defending his doctoral dissertation in 1865, Dmitri Mendeleev was appointed at the University of St. Petersburg as a professor of chemical technology. He also began teaching general chemistry after teaching chemical technology for two years. He stayed as a professor in the University of St. Petersburg until 1890.
In Mendeleev’s early years as a professor of chemical technology, he felt that he could not find any material that is not lacking for his way of teaching. Because of that, he decided to write the book The Principles of Chemistry, which became a classic. During the writing of this book, Mendeleev tried to classify the elements according to their chemical properties. In 1869, the same year his book was published, he published his first version of what became known as the periodic table, in which he demonstrated the periodic law.
In 1871 Dmitri Mendeleev published an improved version of the periodic table, in which he left gaps for elements that were not yet known. From the blanks indicated in his table, Mendeleev was able to predict the existence of elements not yet discovered. His chart and theories gained increased acceptance when three predicted elements gallium, germanium, and scandium were subsequently discovered.
When he initially published the first periodic table of elements in 1869, scientists were not quick to gather as it did not raise much interest among them. However, after Mendeleev deliberately left gaps for elements that are yet to be discovered and even indicated what its chemical properties should be and was then discovered, Mendeleev and his periodic table of elements piqued the attention of the scientific community.
The three elements that Dmitri Mendeleev predicted to be discovered are gallium, scandium, and germanium which was discovered in 1875, 1879, and 1886, respectively. The fact that his predictions was proved in under two decades is quite notable for the scientific community and for which he was recognized internationally and even received various distinctions and awards.
Dmitri Mendeleev’s Contribution to the Periodic Table of Elements
Mendeleev and other chemists had a monumental idea to use the atomic weights of the elements to construct some organizing principle that could relate the elements’ properties to their atomic weights. Mendeleev went to work trying to discern a pattern among the elements. When he arranged the elements according to their atomic weight, he found a pattern not discovered by his predecessors. The pattern had to do with the valence, or combining power, of the elements.
Dmitri Mendeleev discovered a periodic rise and fall of valences, and this led him to construct a table of the elements. The table contained rows, one on top of the other, which reflected the rise and fall of the valences. The columns this produced possessed elements that had similar chemical properties. For example, elements in the first column included lithium, sodium, and potassium, all of which had a valence of 1 and all of which had similar chemical properties. Among the next column s elements were beryllium, magnesium, and calcium, all with a valence of 2 and chemically similar.
Mendeleev called the members of each column a family, to imply a kinship. Today, each column is called a group. Mendeleev gave priority to similarity of properties over atomic weight, and he assigned positions for some elements in columns according to their properties, even though their atomic weights seemed to place them out of order.
He also suggested that the determination of the masses of these elements might be an error. They turned out to be correct, or near enough correct, so that in these cases elements with greater weights preceded elements with lesser weights. However, this did not counteract the general validity of Mendeleev s table.
There was an explanation for these exceptions, but this was not found out until 1913 when English physicist Henry Moseley investigated the X-ray spectra of various atoms. Moseley found that the wavelength of the X rays emitted related directly to the atoms position in the periodic table. This was later found to be due to the protons in the nucleus, which is the atomic number of the element. The discrepancies in atomic weights were proven later to the presence of naturally occurring isotopes (atoms with the same atomic number but different atomic weight).
When Mendeleev finally refined his table so that it included all the then known elements, something perplexing appeared. There were empty places between certain elements. He had deliberately left the places blank, because there were no elements whose properties justified their being in those places. Critics leaped on these omissions, claiming they proved that the concept was seriously flawed. Mendeleev countered by stating that the missing elements would be discovered. Moreover, he boldly predicted what some of their chemical and physical properties would be.
Mendeleev had predicted the properties of three elements; germanium, gallium, and scandium. When these elements were discovered, they were found to possess the properties he had predicted for them. The weight of this evidence was overwhelming, and the periodic table was finally internationally accepted and recognized as the organizing principle of the elements.
The Modern Periodic Table of Elements
Certain changes have been made to the periodic table over time. For example, with the discovery of the electron, and the configurations of the electrons around the atoms of different elements, it became apparent that the arrangement of electrons varied periodically throughout the table. The modern periodic table lists the elements in order of their increasing atomic number, but it organizes them into periods and groups according to their electron configurations.
Dmitri Mendeleev’s development of the periodic table of elements, although notable, is far from perfect. That is why a number of scientists suggested ways to improve it. One of these scientists is Anton van den Broek, an amateur Dutch theoretical physicist. Whereas Mendeleev arranged the elements in his periodic table according to their atomic weights, van den Broek suggested that instead of using the atomic weight, the nuclear charge of the atom is better used to arrange the elements.
Henry Moseley, a physicist working in the University of Manchester, discovered a frequency of fundamental qualities that would be known as the atomic number. This discovery made it possible for scientists to determine how many blank spaces should be allotted in the periodic table of elements. Because of this, scientists have decided to use the atomic number as the way to arrange the elements in the periodic table.
Wolfgang Pauli, an Austrian physicist, in 1924 focused on determining how many elements a period in the periodic table o elements should contain. As a result of his studies, he developed the Pauli Exclusion Principle which states that the same quantum state – quantum numbers – could not possibly contain two electrons as it simply cannot exist. He determined the length of the period based on the order of the elements’ electron-shell filling and quantum-mechanical restrictions.
Scientists don’t run out of things to create and discover. It was back in 2016 that four new elements have been discovered and has filled the gap at the bottom of the periodic table of elements. These recently discovered elements are nihonium, moskovium, tennessine, and oganesson. They have been synthetically-made by scientists in Japan, Russia, and the United States. These four elements finally completed the missing spaces in the periodic table of elements.
After over 200 years of developing and improving the periodic table of elements, it is finally complete. Needless to say, the periodic table of elements is one of the most revolutionary creation of science. Up to this day, the periodic table of elements is known as the heart of the study of chemistry. The periodic table of elements has not remained untouched by time, but instead it has been improved by it while not losing its original purpose and form.
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Dmitri Mendeleev (article). (n.d.). Khan Academy. https://www.khanacademy.org/humanities/big-history-project/stars-and-elements/knowing-stars-elements/a/dmitri-mendeleev
Scerri, E. R. (2011, January 21). The Evolution of the Periodic System. Scientific American. https://www.scientificamerican.com/article/the-evolution-of-the-periodic-system/
Sharp, T. (2017, August 29). Periodic Table of Elements. Live Science. https://www.livescience.com/25300-periodic-table.html