Development of the Periodic Table:

Objectives:

1.    State the periodic law.

2.    Discuss the contributions that Dobreiner, Newlands, Mendeleev, and Moseley made to the periodic table.

Key Terms:

periodic table    periodic law

Web Resources:

Notes:

The periodic table is tool that chemists have developed to organize and categorize the elements found on Earth.  History:
 1700s - about 30 elements known to man 1800s - Dobereiner began classifying elements based on properties into triads Figured out that chemicals in the middle of his triads had properties that were the average of the chemicals that surrounded it

example: (35.5 + 126.9)/2 = 81.2  From this equation he predicted that Bromine should reside between Chlorine and Iodine

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 1865 - Newlands classified the 62 known elements by mass in repeating rows of eight.  Named them octaves but was not taken seriously because of the reference to music.

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 1869 - Mendeleev produced the first periodic table as a logical arrangement of names and properties for his chemistry students.  Arranged them in columns based on similar properties.  He used this arrangement to predict the existence of three new elements.

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 1913 - Moseley determined a way to predict the positive charge in the nucleus of an atom.  He ultimately found that the order of increasing positive charge reflected the chemical and physical properties of the atoms in the periodic table.

Current Periodic table

(www.vcs.ethz.ch/chemglobe/ ptoe/periodic.gif)

Periodic Table of the Elements