Making order out of chaos... the modern periodic table
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Answer:
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Explanation:
While Dobereiner initiated the study of periodic relationship, it was Mendeleev who was responsible for publishing the periodic law for the first time. The first breakthrough in the classification of elements was provided by Mendeleev. He was regarded as the main contributor to the early development of the periodic table. In his periodic table elements were arranged on the basis of their fundamental properties i.e. atomic mass.
A periodic table may be defined as an arrangement which classifies all the known elements on the basis of their properties in such a way that similar elements are placed in the same vertical column while dissimilar elements are placed in different columns.
When he started his work on classification of elements, only 63 elements were known. He carefully examined the relationship between the atomic mass of the element and their chemical and physical properties. Among the chemical properties he concentrated on the compounds formed by the elements with hydrogen and oxygen as they are very reactive and formed compound with most of the elements. Therefore, the formula of oxides and hydrides formed by the elements were taken as the basis of classification of elements.
Mendeleev took 63 cards, each card representing an element, where he wrote down the properties of that element as well as the formulae of its hydride and oxide. He then separated and arranged the elements with similar properties and pinned the cards on the wall one after the other in a vertical column. When he observed these cards after arranging he found that most of the elements automatically got arranged in order of their increasing atomic masses. It was also observed that elements with similar properties occur after a certain interval or In other words there was recurrence of elements with similar physical and chemical properties after a regular interval. On this basis, he formulated a periodic law which states that
“the physical and chemical properties of elements are a periodic function of their atomic masses”.
Periodic function means that the properties of the elements get repeated after certain regular intervals. His law can also be stated as
“when elements are arranged in order of their increasing atomic masses, elements with similar properties are repeated after a certain regular intervals”.
This repetition of properties is called periodicity of properties.