CH 6 - CH 6: The Periodic Table Renee Y. Becker CHM 1025...

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CH 6: The Periodic Table Renee Y. Becker CHM 1025 Valencia Community College 1
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Arrangement of Periodic Table Chemists had been looking for a method to classify the elements. In 1829, the German chemist J.W. Döbereiner observed that several elements could be classified into groups of three, or triad s. All three elements in a triad showed very similar chemical properties and an orderly trend in physical properties. 2
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Organizing the Periodic Table J.A.R. Newlands, in 1865, suggested that the 62 known elements be arranged into groups of seven according to increasing atomic mass. His theory was the law of octaves. He proposed that every eighth element would repeat the properties of the first in the group. His theory was not widely accepted for about 20 years even though it was mostly correct. 3
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Mendeleev’s Periodic Table Mendeleev proposed that the properties of the chemical elements repeat at regular intervals when arranged in order of increasing atomic mass . Mendeleev is the architect of the modern periodic table. 4
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Prediction of New Elements Mendeleev noticed that there appeared to be some elements missing from the periodic table. He was able to accurately predict the properties of the unknown element ekasilicon in 1869. It was discovered in 1886 (germanium). 5
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Noble Gases The periodic table was expanded by one group at the far right of the periodic table with the discovery of argon in 1894. Helium, neon, krypton, xenon, and radon were subsequently discovered in the next 5 years. They were originally called the inert gases . Recently, several compounds of xenon and krypton have been made and the term noble gases is currently used. 6
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Refined Arrangement H.G.J. Moseley discovered that the nuclear charge increased by one for each element on the periodic table. He concluded that if the elements are arranged by increasing nuclear charge rather than atomic mass, the trends on the periodic table are better explained. 7
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The periodic law states that the properties of elements recur in a repeating pattern when arranged according to increasing atomic number. With the introduction of the concept of electron
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This note was uploaded on 10/19/2011 for the course CHEM 1025 taught by Professor Smith during the Spring '10 term at Valencia.

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CH 6 - CH 6: The Periodic Table Renee Y. Becker CHM 1025...

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