SYLLABUS DISCUSSION|CHEMICAL PERIODICITY |L-1|

Chemical Periodicity

Chemical periodicity has been described as the characteristics of elements showing a pattern and recurring variation with increasing atomic number. In the beginning, just 31 elements were known, but currently, 118 elements are known. As a result, studying the chemistry of all the different elements is extremely challenging. Scientists are looking for a systematic technique to rearrange and organize knowledge by categorizing it in order to solve this dilemma.

The Origins of Periodic Classification

Dobereiner’s Triads: In 1817, Johann Wolfgang Dobereiner, a German scientist, attempted to organize substances having similar characteristics into groups. He demonstrated that three elements might be arranged in a triad so that the atomic mass of the middle element is about equal to the average of the atomic masses of the other two elements. As a result, these groupings are known as ‘triads.’ For example, Li has an atomic mass of 6.94, while K has an atomic mass of 39.10. Na, the middle element in this triangle, has an atomic mass of 22.99.

The disadvantages of Dobereiner’s Triads were that these were inapplicable to elements with extremely high and low atomic masses, and this categorization was not applicable to all of the elements.

The Law of Octaves by Newland: In 1866, John Newlands, an English chemist, organized the 56 known elements in order of increasing atomic mass, beginning with hydrogen and ending with thorium. He found a pattern in every eighth element that had qualities identical to the first one. He linked these parallels to musical octaves. As a result, it is known as Newland’s Law of Octaves. The disadvantages of the octaves law are that it is only relevant up to Ca, and after Ca, every eighth element does not have attributes identical to the first. When Newland issued this legislation, there were only 56 elements in nature, but since then, many elements have been found. As a result, the remaining components and their attributes did not adhere to the law of octaves.

Mendeleev’s Periodic Table: In 1869, Russian scientist Dmitri Ivanovich Mendeleev developed a Periodic rule. He began his investigation with just 63 known elements. He discovered a link between the elements’ atomic masses and their physical and chemical qualities, as well as a periodic recurring trend with comparable physical and chemical attributes.