Early History of the Periodic
Table
Ck12 Science
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Printed: February 28, 2013
AUTHOR
Ck12 Science
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C ONCEPT
Concept 1. Early History of the Periodic Table
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Early History of the Periodic
Table
• Describe Dobereiner’s triad approach to organizing elements.
• Describe Newland’s Law of Octaves.
When you go to the library to find a book, how do you locate it?
If it is a fiction book, you look by author since the fiction materials are filed by the author’s last name. If you are
looking for a non-fiction publication, you look in a catalog (most likely on a computer these days). The book you
are looking for will have a number by the title. This number could refer to the Dewey Decimal system, developed
by Melvil Dewy in 1876 and used in over 200,000 libraries throughout the world. Another system in wide use is
the Library of Congress approach, developed in the late 1800s-early 1900s to organize the materials in the federal
Library of Congress. This method is one of the most widely used ways to organize libraries in the world. Both
approaches organize information so that people can easily find what they are looking for. Chemistry information
also needs to be organized so we can see patterns of properties in elements.
Early Attempts to Organize Elements
By the year 1700, only a handful of elements had been identified and isolated. Several of these, such as copper and
lead, had been known since ancient times. As scientific methods improved, the rate of discovery dramatically
increased. With the ever-increasing number of elements, chemists recognized that there may be some kind of
systematic way to organize the elements. The question was: how?
A logical way to begin to group elements together was by their chemical properties. In other words, putting elements
in separate groups based on how they reacted with other elements. In 1829, a German chemist, Johann Dobereiner
(1780-1849), placed various groups of three elements into groups called triads. One such triad was lithium, sodium,
and potassium. Triads were based on both physical as well as chemical properties. Dobereiner found that the
atomic masses of these three elements, as well as other triads, formed a pattern. When the atomic masses of
lithium and potassium were averaged together (6.94+39.10)
= 23.02, it was approximately equal to the atomic mass
2
of sodium (22.99). These three elements also displayed similar chemical reactions, such as vigorously reacting with
the members of another triad: chlorine, bromine, and iodine. While Dobereiner’s system would pave the way for
future ideas, a limitation of the triad system was that not all of the known elements could be classified in this way.
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English chemist John Newlands (1838-1898) ordered the elements in increasing order of atomic mass and noticed
that every eighth element exhibited similar properties. He called this relationship the “Law of Octaves.” Unfortunately, there were some elements that were missing and the law did not seem to hold for elements that were heavier
than calcium. Newlands’s work was largely ignored and even ridiculed by the scientific community in his day. It
was not until years later that another more extensive periodic table effort would gain much greater acceptance and
the pioneering work of John Newlands would be appreciated.
Summary
• Johann Dobereiner organized elements in groups called triads.
• John Newland proposed the “law of Octaves” for organizing the elements.
Practice
Use the link below to answer the following questions:
http://www.bpc.edu/mathscience/chemistry/history_of_the_periodic_table.html
1.
2.
3.
4.
Who discovered the first element through scientific inquiry and what was the element?
Describe the triad approach to constructing a periodic table.
What contribution did A.E.Beguyer de Chancourtois make to the development of the periodic table?
Why did John Newlands call his approach the Law of Octaves?
Review
1.
2.
3.
4.
5.
6.
List some elements known since ancient times?
What properties were the basis of the triad system?
Why did Dobereiner believe that lithium, sodium, and potassium belonged in a triad?
What was a shortcoming of the triad system?
How did Newlands arrange the element?
What was a problem with the “Law of Octaves"?
• triad: In 1829, a German chemist, Johann Dobereiner (1780-1849), placed various groups of three elements
into groups called triads. One such triad was lithium, sodium, and potassium. Triads were based on both
physical as well as chemical properties. Dobereiner found that the atomic masses of these three elements, as
well as other triads, formed a pattern.
• octave: English chemist John Newlands (1838-1898) ordered the elements in increasing order of atomic mass
and noticed that every eighth element exhibited similar properties. He called this relationship the “Law of
Octaves.”
2