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The History of the Periodic Table

The Periodic Table creates the foundation in which all chemistry is based. It is what ties all of the elements of the science together and makes it work. The Periodic Table as we know it today is very different from the early versions, when only one third of the elements were known to man. When I first started this class, I was prepared to be bored silly because of my hatred of it in high school. However, I became interested in the topic and decided to do some outside research to write this essay in order to give myself the chance to do justice to the formation of this ncredible table that has managed to organize an entire science.

In order to explain all the different aspects and people that went into the creation of the table, we will start with Lavoisier and his concept of elements, then to Dalton and his concept of atoms, then move to Berzelius and the development of atomic weights, then continue with Mendeleev and the predictive nature of the Periodic Table, and finish with Moseley and his concept of atomic numbers. Antoine Lavoisier introduced the system of chemical nomenclature. He rote the first modern chemical textbook, which contained a list of 33 elements, or substances that could not be broken down further.

The elements were grouped them into four categories on the basis of their chemical properties: Simple substances belonging to all the kingdoms of nature, which may be considered as the elements of bodies (now known as gases), simple substances that were not metallic (nonmetals), simple metallic bodies (metals), and simple Earthy substances (earths). In the first category he listed substances that we now know as oxides but hich at the time had defeated all attempts at separation. It was rough and not well organized, but it was definitely something to build on.

John Dalton was an English meteorologist who switched to chemistry when he saw the applications for chemistry of his ideas about the atmosphere. He proposed the Atomic Theory in 1803 which stated that: all matter was composed of small indivisible particles termed atoms, atoms of a given element possess unique characteristics and weight, and three types of atoms exist – simple (elements), compound (simple molecules), and complex (complex molecules). Since the old chemical symbols were not fit to use in his theory, he proposed a new set of standard symbols for the chemical elements.

Dalton’s symbols, however, were not very easy to memorize. Yet, they did have some benefits: each symbol represented one atom and the formula of a compound was made up of the symbols of its elements, it showed how many of these atoms were present in the molecule. A few years later Dalton’s system was superseded with the chemical symbols and formula by Jons Berzelius. Berzelius is who we can credit for the chemical “symbols” that we use oday. As with Dalton’s symbols, the symbol for newly discovered elements was a letter or two letters in a circle.

It is therefore quite logical that a few years later, in Sweden, Berzelius suggested just using letters, arguing those are easier to write and print than symbols. The basis for his symbols are the Latin names of the elements. With some modifications, Berzelius’ symbols are the ones that we use today. There were only 47 elements at this time, however this model of identifying the elements has been used as elements have been discovered. He also discovered four more elements because he understood the concept of atomic weights and realized that there were definitely gaps missing between certain elements.

His understanding of these weights which led to his discoveries is due to the fact that he was the first to accurately determine the atomic weights of the known elements. Dimitri Mendeleev, known as the father of the periodic table, had in 1869 assembled detailed descriptions of more than 60 elements and, on 6 March 1869 a formal presentation was made to the Russian Chemical Society ntitled “The Dependence Between the Properties of the Atomic Weights of the Elements.

There were eight points to his presentation: 1) the elements, if arranged according to their atomic weights, exhibit an apparent periodical change of properties, 2) elements which are similar as regards their chemical properties have atomic weights which are either of nearly the same value or increase regularly, 3) the arrangement in the order of their atomic weights corresponds to their distinctive chemical properties, 4) the elements which are the most widely diffused in nature ave small atomic weights, 5) the magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body, 6) The discovery of many as yet unknown elements is expected, 7) Some atomic weights are expected to be corrected, and finally 8) from this table, new analogies between elements can be predicted.

His process in which he discovered all this was actually quite simple – he sat down and wrote the elements and their masses on pieces of paper and patiently arranged them while looking for patterns in is organization. In 1870, Mendeleev took his concept even further by stating that it was possible to predict the properties of undiscovered elements. He then proceeded to make predictions for three new elements and suggested several properties of each. Many scientists scoffed at Mendeleev’s predictions.

In 1875, one of the predicted elements was discovered and Mendeleev’s ideas were taken seriously. The other two elements were discovered later and their properties were found to be remarkably similar to those predicted by Mendeleev. There was a problem ith Mendeleev’s table. If the elements were arranged according to increasing atomic masses, Tellurium and Iodine seemed to be in the wrong columns. Their properties were different from those of other elements in the same column. However, they were next to each other. This was also the case with Cobalt and Nickel. Henry Moseley found the key to solving this problem. When Argon was discovered, the masses of Argon and Potassium were reversed.

He found the reason for these apparent exceptions to the rule. As a result of Moseley’s work, the periodic law was revised. He stated that physical and chemical properties are a periodic function of their atomic number, rather than their mass. This better explained the gaps in the table. The atomic number of an element indicates the number of protons in the nucleus of each atom of the element. The atomic number also indicates the number of electrons surrounding the nucleus. Herewith he created the modern periodic table in which each succeeding element has one more proton and electron than the former element. This is the periodic table in which we all know and love.

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