"What the ocean is to a child, the periodic table is to a chemist" - Karl Barry Sharpless, American chemist
There have been several proposals and tests to group elements with similar properties. In 1789, French chemist Antoine Lavoisier grouped the elements as metals and nonmetals. Later German physicist Johann Wolfang Döbereiner identified that a few elements were chemically and physically similar. He arranged them in groups of three in the increasing order of atomic weight. Each of them was named a Triad. In every triad, certain properties of the middle element, mainly the atomic weight, were approximately equal to the average value of the other two elements in the triad.
British chemist John Newlands was the first to arrange the elements into a periodic table in the order of increasing atomic mass. He found that every eighth element had similar properties. They were named ‘Octaves’. He arranged the elements into eight groups. But this law was applicable only up to calcium and hence it failed.
In the 1860s, the elements were classified into two categories- either based on their atomic weight or their common properties. In 1869 the Russian Chemist Dimitri Mendeleev worked towards giving a classification in which all the elements come under one roof. Mendeleev's inspirations are fascinating. Initially, he drew inspiration from the game solitaire. In a way similar to the game, he made separate cards for each of the then-known 63 elements. He wrote their atomic weights and each of their properties in them. Mendeleev carried the cards with him during a train journey on February 17th, 1869. During the three-day-long journey, he worked tirelessly on arranging the cards to get a meaningful pattern. He noticed that the atomic masses did not appear to be arranged in a logical order. Exhausted Mendeleev went to sleep and dreamt of a table where he saw all the elements arranged in a neat order. He woke up immediately and noted it down. EUREKA!! Yes! A dream is what laid the bricks for building the periodic table. He named it “The periodic table of elements”.
Mendeleev’s table led to the formation of the “Periodic Law”. The famous periodic law states that ‘When the elements are listed in order of increasing atomic weights, their properties vary periodically’. This led to the understanding that when we go vertically down a list of elements, certain similar properties can be observed among them. To emphasize this periodic repetition of similar properties, Mendeleev arranged the symbols and atomic weights of the elements in the form of a table. Each vertical column of this periodic table contains a group or family of related elements. The alkali metals are in Group I, alkaline earth in Group II, chalcogens in Group VI, and halogens in Group VII. Each horizontal row was called a period. But while constructing the elemental table, Mendeleev discovered that there were some blank spaces. He realised that they must be spaces for elements that are yet to be found. Mendeleev, therefore, left blank spaces for undiscovered elements and predicted their properties by averaging the characteristics of other elements in the same group.
The table Mendeleev devised had some flaws, just as many discoveries do. In his periodic table Cobalt, which has an atomic mass of 58.9au precedes Nickel whose atomic mass is 58.6au. Similarly, Tellurium (127.6) has a higher atomic mass than Iodine (126.9) but precedes it in the periodic table. Hence these do not obey Mendeleev’s periodic law. The other flaws include the arrangement of chemically dissimilar elements, neglection of the position of isotopes and anomaly regarding the position of Hydrogen. But despite all the flaws, this table served as the prerequisite for Henry Mossey to introduce the modern periodic table. When Mendeleev formulated his table, chemists at that time weren’t aware of the internal structure of an atom. So in the 20th century, Henry Moseley, taking into account the atomic structure, proposed that the atomic number of an element is a more fundamental property than its atomic mass. And that is how the modern periodic table was born and a Modern periodic law was given. But if not for Mendeleev's table and discovery, it wouldn’t have been possible that an elemental guide with great precision would exist.
With the discovery of every new element, the periodic table was updated. Two new periods Actinides and Lanthanides were included in the table. The modern periodic table is based on atomic numbers, so many problems faced by Mendeleev’s table were resolved. Currently, the periodic table holds with it 118 elements. Of these only 94 elements are naturally occurring, the rest of the elements are synthesized in the labs. They tend to exist for a short span of time. Many trends were studied using this table, which paved the way for the understanding of many of the elements and their properties. Today’s periodic table has undergone various reformations to give a table that serves as a dictionary for every chemist. Currently, the periodic table is controlled by IUPAC. 2019 marked the 150th year of the anniversary of the Periodic Table. In 2017, the United Nations General Assembly announced that 2019 would be celebrated as the International Year of the Periodic Table. Various events and celebrations took place throughout the year to mark the discovery of this dictionary. A periodic song was also composed including every element in the table. The latest elements that made it to the table were Nihonium (113), Moscovium (115), Tennessine (117), and Oganesson (118), in the year 2016. As a tribute to The Father of the Periodic Table - Mendeleev, the 101st element is named Mendelevium. Natural Astatine (At) is the rarest element on earth, present in less than 1gram on the Earth's surface.
It was not essential that Mendeleev's dream had to be accurate, so scientists came up with alternative arrangements. Chemist and author John Clark created a race-track periodic table in 1993. In 1960, Theodor Benfey framed a snail-shaped periodic table. Chemist James F. Hyde created a curled-ribbon periodic table in 1975. And in 2019, the European Chemical Society (EuChemS) developed a table to explain to the people about element scarcity. They designed it in such a way that each element occupied an area that was equal to its quantity on the earth, It focused mainly on 30 elements that are being used extensively for smartphones. Adding to this, in 2019 mathematicians at the Max Plank Institute represented the elements in a hypergraph.
The periodic table is a fantastic discovery that is used by scientists all over the world. Many chemists find the table to be an invaluable tool, even though it has a few debatable facts. By creating this table Mendeleev performed a primitive version of the purpose of machine learning classification and information about physical and chemical properties. From performing a simple experiment to building atomic clocks, elements are of great importance in every field. A better understanding is therefore possible when the various elements present are grouped together. It is a table of knowledge and a fountainhead of innovation in many areas. This poster isn't just something you see in chemistry classes, it's a wealth of information for generations to come.
Other types of periodic tables-
- M. Valliammai
Amazing read Valliammai!