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Transcript
A Quick Look at the History of the Periodic Table
Things are different from each other, and each can be reduced
to very small parts of itself. - Ancient knowledge
This was noticed early by people, and Greek thinkers, about 400BC, used the words
"element', and `atom' to describe the differences and smallest parts of matter. These ideas
survived for 2000 years while concepts such as `Elements' of Earth, Fire, Air, and Water
to explain `world stuff' came and went.
Much later, Boyle, an experimenter like Galileo and Bacon, and who was influenced
much by Democritus, Gassendi, and Descartes, lent important weight to the atomic
theory of matter in the 1600s.
The familiar periodic table that adorns many science classrooms is based on a number of
early efforts to identify and classify the elements. In the 1790’s, one of the first lists of
elements and their compounds was compiled by French chemist Antioine-Laurent
Lavioser. It was Lavoisier who divided the few elements known in the 1700's into four
classes, and then John Dalton made atoms even more convincing, suggesting that the
mass of an atom was it's most important property.
"The chemical elements are composed of... indivisible particles of matter, called
atoms... atoms of the same element are identical in all respects, particularly
weight." - Dalton
In the early 1800's Dobereiner noted that similar elements often had relative atomic
masses, and DeChancourtois made a cylindrical table of elements to display the periodic
reoccurrence of properties.
Cannizaro determined atomic weights for the 60 or so elements known in the 1860s, then
a table was arranged by Newlands, with the elements given a serial number in order of
their atomic weights, beginning with Hydrogen.
This made evident that "the eighth element, starting from a
given one, is a kind of repetition of the first", which Newlands
called the Law of Octaves.
Both Meyer and Mendeleyev constructed periodic tables
independently, Meyer more impressed by the periodicity of
physical properties, while Mendeleyev was more interested in
the chemical properties.
"...if all the elements be arranged in order of their atomic
weights a periodic repetition of properties is obtained." Mendeleyev
History of the Periodic Table
1
C. Pace, Instructor
Mendeleyev published his periodic table & law in 1869 and
Dimitri Mendeleyev
forecast the properties of missing elements, and chemists
began to appreciate it when the discovery of elements
predicted by the table took place. The periodic tables have always been related to the
way scientists thought about the shape and structure of the atom, and has changed
accordingly.
The `modern' periodic table is very much like a later table by Meyer, arranged, as was
Mendeleyev's, according to the size of the atomic weight, but with Group 0 added by
Ramsay. Later, the table was reordered by Mosely according to
atomic numbers (nuclear charge) rather than by weight.
Although Mendeleev's table demonstrated the periodic nature of the
elements, it remained for the discoveries of scientists of the 20th
Century to explain why the properties of the elements recur
periodically.
In 1911 Ernest Rutherford published studies of the scattering of alpha
particles by heavy atom nuclei which led to the determination of
nuclear charge. He demonstrated that the nuclear charge on a nucleus
was proportional to the atomic weight of the element. Also in 1911,
A. van den Broek in a series of two papers proposed that the atomic
weight of an element was approximately equal to the charge on an
atom. This charge, later termed the atomic number, could be used to
number the elements within the periodic table.
Ernie Rutherford
In 1913, the results of his measurements of the wavelengths of the xray spectral lines of a number of elements which showed that the
ordering of the wavelengths of the x-ray emissions of the elements
coincided with the ordering of the elements by atomic number. With the
discovery of isotopes of the elements, it became apparent that atomic
weight was not the significant player in the periodic law as Mendeleev,
Meyers and others had proposed, but rather, the properties of the
elements varied periodically with atomic number.
Henry Moseley
Harry D. Hubbard, of the United States
National Bureau of Standards, modernized
Mendeleyev's periodic table, and his first work
was published in 1924. This was known as the
"Periodic Chart of the Atoms".
Into the 1930s the heaviest elements were being put up in the body
of the periodic table, and Glenn Seaborg "plucked those out" while
working with Fermi in Chicago, naming them the Actinide series,
History of the Periodic Table
2
C. Pace, Instructor
Glenn Seaborg
which later permitted proper placement of subsequently 'created' elements - the
Transactinides, changing the periodic table yet again. These elements were shown
separate from the main body of the table. When Seaborg examined the Alexander
Arrangement, he said that it was correct, and later told a photographer that it was his
favorite periodic table.
The last major changes to the periodic table resulted from
Glenn Seaborg's work in the middle of the 20th Century.
Starting with his discovery of plutonium in 1940, he discovered
all the transuranic elements from 94 to 102. He reconfigured
the periodic table by placing the actinide series below the
lanthanide series. In 1951, Seaborg was awarded the Nobel
Prize in chemistry for his work. Element 106 has been named
seaborgium (Sg) in his honor.
Glenn Seaborg
During Glenn Seaborg's work on nuclear energy in the
Manhattan Project during WWII he first placed the then new
radioactive elements in a separate location. Before he died he
had an Alexander Arrangement and determined that this 3-D
method was now the correct way to show the Rare Earths.
The Alexander Arrangement of the Elements, a three-dimensional periodic chart
designed and patented by Roy Alexander and introduced in 1994, retains the separate
Lanthanide and Actinide series, but integrates them at the same time, made possible
by using all three dimensions.
Further improvement provided by the Alexander
Arrangement of the Elements is location of all the
element data blocks in a continuous sequence
according to atomic numbers while retaining all
accepted property interrelationships. This eases use &
understanding of the immense correlative power of the
periodic chart in teaching, learning, and working with
chemistry.
History of the Periodic Table
3
C. Pace, Instructor