Dmitri Ivanovich Mendeleev is known as the most important contributor to the early development of a Periodic Table of elements wherein the elements were arranged on the basis of their fundamental property, the atomic mass, and also on the similarity of chemical properties. When Mendeleev started his work, 63 elements were known. The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element for its classification. He then took 63 cards and on each card he wrote down the properties of one element. He sorted out the elements with similar properties and pinned the cards together on a wall. He observed that most of the elements got a place in a Periodic Table and were arranged in the order of their increasing atomic masses. It was also observed that there occurs a periodic recurrence of elements with similar physical and chemical properties.
In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass. Mosley bombarded different metal targets with high speed electrons and measured frequencies of X rays emitted. He observed regularities in the characteristic X-ray spectra of the elements. A plot of √ν (where ν is frequency of X-rays emitted) against atomic number (Z) gave a straight line and not the plot of √ν vs atomic mass. He thereby showed that the atomic number is a more fundamental property of an element than its atomic mass. Mendeleev’s Periodic Law was, therefore, accordingly modified.
Various scientific and psychological studies have proven the actual result of memorization techniques on children’s memory. According to the results of tests performed, scientists witnessed a guaranteed increase in the speed of reading and memorization at a minimum of 50% after these techniques have been adopted. It can improve young children’s cognitive development, memory retention skills, and the results they achieve in school.
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