History of the Periodic Table
An early attempt was made by a German Chemist named Johann Dobereiner, in 1817.
Dobereiner noticed that there were several groups of three elements which shared certain
properties. For example; chlorine, bromine and iodine all share antiseptic properties.
Dobereiner called each group of three elements with similar properties a "triad". He also
noticed that when he arranged the elements of a triad by atomic mass, the middle element had
an atomic mass that fell close to the middle of the other two atomic masses.
Almost fifty years later, an English Chemist named John Newlands proposed an updated
classification system. Newlands had noticed that when the 49 known elements were arranged
in order of increasing atomic masses, certain properties would repeat every eighth element.
He arranged the elements into seven groups of seven elements and called his system the "law
of octaves."
In the 1860's a German Chemist named Lothar Meyer was developing a periodic table
based on the idea that when the elements were arranged by atomic mass, certain properties
were repeated periodically.
In 1869 Dimitri Mendeleev, a Russian Chemist, published the first periodic table. It had
eight columns, and it contained blank spaces for elements that Mendeleev predicted must
exist, although they had not yet been discovered. His predictions turned out to be correct.
New elements were discovered, and they fit into the spaces that he had left in his periodic
table.
It was not until 1914 that Henry Moseley corrected the periodic law, based on his
discovery of the atomic numbers of several elements. This modern periodic law states, "The
periodic properties exhibited by the elements are a function of the atomic numbers." Dmitri Mendeleev
Dmitri Mendeleev, a Russian scientist born in Tobolsk, Siberia in
1834, is known as the father of the periodic table of the elements. The
periodic table of the elements is an important tool used by students and
chemists around the world to help them understand and simplify the
often complex world of chemical reactions.
Not only did Mendeleev arrange the periodic table of the elements, he
also wrote and published a 2 volume chemistry book entitled Principles of Chemistry as there
was no thorough chemistry textbook at the time. Mendeleev dedicated his life to research and
education. Mendeleev made it his special responsibility to educate people wherever he went.
When he traveled, Mendeleev would ride in the third class section of the train just to share
findings with peasants over a cup of tea. Mendeleev died on January 20, 1907 at the age of
73.
http://web.buddyproject.org/web017/web017/history.html http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson34.htm The Big Task
Mendeleev set out to identify a pattern in the elements.
Mendeleev looked at many pieces of evidence and made an
important observation that some elements have similar chemical
and physical properties. Mendeleev's hunch was that these
similarities were the key to unlocking the hidden pattern of the
elements. Mendeleev then embarked on the tedious task of
organizing all known information for every element to help him
decipher the pattern.
To begin his task, Mendeleev wrote facts about the elements on individual paper cards. On these
cards, Mendeleev wrote information such as the elements' melting points, densities, colors, atomic
masses (the average mass of one atom of that element), and bonding powers (the number of
chemical bonds an element can form).
Once Mendeleev's cards were made, he
tried arranging them in various ways.
Finally, Mendeleev noticed that patterns
appeared when the elements were
arranged in order of increasing atomic
mass. One of the trends that he noticed
showed that the bonding power of the
elements from lithium to fluorine change
in an orderly way. For example, after
fluorine, the next heaviest element
Mendeleev knew was sodium, which has
the same bonding power as lithium.
Using this knowledge, Mendeleev placed
the card for sodium below the card for
lithium. This worked well -- as he laid
out cards, each element had properties
similar to the elements above and below
it.
Mendeleev's table was not perfect,
however. Arranging the elements by
increasing atomic mass left three blank
spaces in the table. Despite this
development, however, Mendeleev boldly proposed that these blank spaces would be filled by
elements that had not yet been discovered. Mendeleev was even able to use the patterns in his table
to predict the properties of these undiscovered elements. This first periodic table of the elements was
published in 1869. The word "periodic" means that there is a repeating pattern -- that is, the
properties of the elements repeat with each row -- or period -- of the table.
Amazingly, within 16 years of Mendeleev's first periodic table, chemists had discovered all three of
the missing elements (scandium, gallium, and germanium), and their properties were very close to
what Mendeleev had predicted.
Name_________________________________________ Pd_________ Date______________________________ History of the Periodic Table QUESTIONS: 1. Why is Mendeleev’s work with the Periodic Table considered great? 2. How did Mendeleev arrange the elements in the periodic table? 3. Why has the Periodic Table changed over time?