History of the Periodic Table

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The modern periodic table of the elements is a chemist's must-have for doing many of the things required by the profession. It helps them predict properties of elements such as chemical reactivity, state of matter, and electron configuration. Though this diagram seems flawless, it hasn't always been that way. The periodic table of the elements has a long history.

The search for an arrangement of the different elements began with the ancient Greek philosophers about 2500 years ago. They believed everything was composed of air, earth, water, fire, or a combination of these four elements. However, they began to find exceptions to this rule. Though they were astute observers of nature, they didn't tests their hypotheses with experiments.

The next major development in the history of the periodic table came in 1829. By this time, scientists had realized that there were many more elements in the world than the Greek air, earth, water, and fire. During this year, the German chemist J. W. Dobereiner classified elements into groups of three, which he called triads. The elements in these triads all had similar chemical properties, and their physical properties varied in a predictable way according to their atomic masses. One such triad is the halogen triad which includes chlorine, bromine, and iodine. These triads laid the foundation for future development of the periodic table.

The next, and probably the most famous contributor to the development of the periodic table was Dmitri Mendeleev. He was a Russian professor of chemistry at the University of St. Petersburg, and he realized that the properties of elements repeated themselves periodically if they were organized by atomic mass. Mendeleev published a periodic table in 1869. In this periodic table, the elements were arranged by atomic mass. He placed elements in vertical columns with the lightest elements being at the top and the heaviest being at the bottom.

Mendeleev later published an improved version of the periodic table with the elements arranged in horizontal rows. In this version, elements were arranged so that elements in vertical columns had similar properties, and the properties of elements repeated themselves in each horizontal row. This repeated occurrence of properties is known as periodicity. This periodic table is very similar to the one we have today. Mendeleev was so confident in his theory of periodicity that he began to place elements with other similar elements, even if their atomic masses were not in the correct place. He also left blank spaces in the table, which he said represented undiscovered elements.

Mendeleev was largely correct in his placement of elements. In the modern periodic table, elements are arranged by atomic number, rather than atomic mass. Though Mendeleev didn't realize it, this is exactly what he was doing in his periodic table.

The search for a diagram of the elements has been long in the making. Starting with the Greek philosophers and ending with Mendeleev, the periodic table is now an accurate and clear representation of the elements that aids chemists all over the world.

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