Attempts Made By Johann Dobereiner And Johann Newlands To

Classify The Elements

Done by Mah Kim Chuan, James

Of class 1O2

1817-First attempt to arrange the elements by Johann Dobereiner

1829-Law of Triads by Dobereiner 1829 to 1858-Extension of elements beyond

the triads 1863-Attempt to classify the known

elements by Johann Newlands *1862-A glimpse into de Chancourtois 1863-Law of Octaves

Content page

Born on Dec 13, 1780, at Hof an der Saale, Germany.

Studied at the University of Jena Became an assistant professor and then a

supervisor of science instruction Died on March 24, 1849.

Short Introduction of Dobereiner

The development of the periodic table begins with Johann Dobereiner (1780-1849) who grouped elements based on similarities. In 1817 Dobereiner noticed that certain elements that were chemically similar could be grouped together in threes, for example, calcium, strontium, and barium; lithium, sodium, and potassium; chlorine, bromine, and iodine

First attempt to arrange the elements by Johann Dobereiner

Calcium (atomic weight 40), strontium (atomic weight 88), and barium (atomic weight 137) possess similar chemical prepares. Dobereiner noticed the atomic weight of strontium fell approximately midway between the weights of calcium and barium: Ca Sr Ba (40 + 137) ÷ 2 = 88 40 88 137

How could certain elements be grouped in threes?

Was the arrangement of elements just a coincidence or a pattern? Through further experimentations, Dobereiner noticed the similar pattern for the alkali metal triad (Li/Na/K) and the halogen triad (Cl/Br/I).

Li Na K (7+39) ÷ 2 =237 23 39

Cl Br I (35+127) ÷ 2 =8135 80 127

Twice a coincidence, Thrice a pattern

Definition- Middle element in the triad had atomic weight that was the average of the other two members

However, not all chemists accept his theory because only a few elements were known, and not all of them were fitted into triads.

The Law of Triads by Dobereiner

During this time fluorine was added to the halogen group; oxygen, sulphur, selenium and tellurium were grouped into a family while nitrogen, phosphorus, arsenic, antimony, and bismuth were classified as another. Unfortunately, research in this area was hindered by the fact that accurate atomic values of elements were not always available.

Elements extended in the triad family

Born on 26 November 1837, at London First person to devise a Periodic Table of

elements. Studied at the Royal College of Chemistry Furthered Döbereiner’s work and published

the Law of Octaves. Died on 29 July 1898

Another introduction of Johann Newlands

The English chemist John Newlands also attempted to classify the known elements of his day based on their atomic weight. *Like de Chancourtois, he noticed a repeating pattern—every eighth element had similar physical or chemical properties.

1863-Attempt to classify the known elements by Johann Newlands

Alexandre Beguyer de Chancourtois (1820-1886), professor of geology at the School of Mines in Paris, published in 1862 a list of all the known elements. The list was constructed as a helical graph wrapped around a cylinder--elements with similar properties occupied positions on the same vertical line of cylinder. However, his ideas were ignored as his works were published without a diagram.

A glimpse into de Chancourtois

The concept of periodicity in the properties of the chemical elements was first formulated by Johann Newlands. He classified 56 elements into 11 groups based on their physical properties. In 1863 he wrote a paper proposing the Law of Octaves.

Law of Octaves

In the group of 8, the last element showed properties of first element and this periodicity was just like the notes of music ( Sa, Ree, etc.).

Theory of The Law of Octaves

Newlands saw a pattern in which intervals of seven elements often separated elements with similar chemical properties.

This reminded him of a musical scale, in which one note in a key is separated from its octave by an interval of seven notes. Newlands was so fascinated by this "law of octaves" that he made the mistake of trying to force the elements into this pattern.

Why was it wrong?

Eventually, a Russian scientist, Dmitry Mendeleev discovered that on arrangingin the increasing order of atomic mass, elements with similar chemical properties occurred periodically.

He named his observation as Mendeleev’s Periodic Law.

Classification of the Elements

The chemical and physical properties of elements are a periodic function of their atomic masses.

An arrangement of the elements in a table based on the above law is called periodic table.

Mendeleev’s Periodic Law

Example of a Periodic table.

The Periodic Table

Henry Moseley, an English physicist discovered in the year 1913 that atomic number is the most fundamental property of an element, instead of its atomic mass

Atomic number of an element is the number of protons in the nucleus of its atom.

Modern Classification

After the discovery of atomic numbers, the periodic law was modified and the new law was based upon atomic numbers in place of atomic masses of elements.

Modern Periodic Law

“Development of Periodic Table”http://web.fccj.org/~ethall/period/period.htm Tan Jia Ern, Josiah. “Attempts Made By Johann Dobereiner And Johann Newlands To Classify

The Elements”http://2a307science.blogspot.com/2011/09/normal-0-false-false-false-en-sg-zh-cn.html September 7, 2011 Information Please® Database, © 2007 Pearson Education. “The Periodic Table” http://www.infoplease.com/ipa/A0905215.html Thomson, Freddy. “Earlier attempts on classification of Elements”http://www.indiastudychannel.com/resources/143949-Earlier-attempts-classification-Elements.aspx August 12, 2011 ©2012 Encyclopædia Britannica. “Johann Wolfgang Döbereiner”http://www.britannica.com/EBchecked/topic/167249/Johann-Wolfgang-Dobereiner Wikipedia, the free encyclopedia. “John Alexander Reina Newlands”http://en.wikipedia.org/wiki/John_Alexander_Reina_Newlands April 4, 2012 “Periodic Classification of Elements” http://www.nios.ac.in/secscicour/chapter04.pdf “Electron Configurations and the Periodic Table” Online Image. KentChemistryHOME. May, 2012

Bibliography

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