History of the Periodic Table
The periodic table was founded during the 1800’s due to the contributions of three main scientists; John Newlands, Dmitri Mendeleev, and Henry Moseley. - In 1865, John Newlands proposed the ‘Law of Octaves’, which stated that every eighth element shared similar properties (eg. Lithium, Sodium, and Potassium). This allowed him to group elements in a similar structure to the current periodic table and thus predict the properties of some elements, however, this was still not completely accurate and the Law of Octaves was not always consistent. - In addition to this theory, Dmitri Mendeleev, in 1869, proposed the law of periodicity, which notes that if elements were arranged in order of increasing atomic mass, elements with similar properties would occur at regular intervals (“The physical and chemical properties of elements are periodic functions of their atomic mass.”) This was an extension of Newlands’ Law of Octaves, as Mendeleev had now arranged elements in order of atomic mass. As an example, Mendeleev proposed that Hydrogen, Lithium, Sodium, Rubidium, and Caesium would all be part of ‘group 1’ of his Periodic Table, as they all shared patterns in atomic mass. These became the foundations of the current Periodic Table, allowing for the presumptions to be made about the properties of elements on the basis of atomic mass and structure (eg. Mendeleev hypothesised of an element, Eka-Boron, which had an atomic mass of 44, and shared various properties such as a specific gravity of 3.5, which was later discovered to be Scandium, with an atomic mass of 43.79 and specific gravity of 3.864.) - As a most recent contribution to the periodic table, in 1913, Henry Moseley proposed the Atomic Theory and subjected known elements to x-rays to seek protons and atomic numbers, which arranged elements according to increasing atomic numbers, and not atomic masses, (eg. Carbon, Nitrogen, and Oxygen were all chronologically increasing in relation to...
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