Periodic Classification of Element — Flashcards

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Elements are classified as metals, nonmetals, and metalloids. Metals lie on the left side of the zig-zag line, nonmetals lie on the right side, and metalloids lie along the border of the zig-zag line.

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As more elements were discovered, their properties became difficult to study one by one. Classification made it easier to study patterns and similarities among elements.

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A triad is a group of three elements with similar chemical properties. Dobereiner showed that the atomic mass of the middle element is approximately equal to the mean of the atomic masses of the other…

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Mean = (a + c)/2 = (6.9 + 39.1)/2 = 46.0/2 = 23.0. This matches sodium, so Li, Na, K form a Dobereiner triad.

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All the known elements could not be arranged into triads. The method had limited applicability and could not classify every element.

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Newlands found that when elements were arranged in increasing order of atomic mass, every eighth element had properties similar to the first. He compared this with octaves in music.

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Sodium is the eighth element from lithium, and both have similar properties. This supports the idea of repeating properties after every eighth element.

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The law was applicable only up to calcium. It also could not accommodate newly discovered elements later on.