Classification of Elements- The Periodic Table — Flashcards

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As the number of known elements increased, it became difficult to remember the properties of each element and its compounds. A systematic arrangement made it easier to study, compare, and predict elem…

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Robert Boyle defined an element as any substance that cannot be decomposed into a further simple substance by a physical or chemical change.

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About 63 elements were known by 1865.

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Elements with similar properties can be arranged in groups of three. When arranged in increasing atomic weights, the atomic weight of the middle element is the average of the first and third.

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Atomic weight of middle element = (7 + 39) / 2 = 46 / 2 = 23. So the middle element has atomic weight 23.

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It did not work for all known elements. It failed for very low mass and very high mass elements, and some elements like chlorine did not fit the average rule exactly.

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When elements are arranged in increasing atomic weights, every eighth element has properties similar to the first element.

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It was restricted to only 56 elements, so there was no room for later-discovered elements. It also placed some dissimilar elements together and had two elements in the same slot in some cases.