-: Periodic Table Historical View :-
Initiatory :-
A necessary prerequisite to the construction of the periodic table was the discovery of the individual elements. Although elements such as gold, silver, tin, copper, lead and mercury have been known since antiquity, the first scientific discovery of an element occurred in 1649 when Hennig Brand discovered phosphorous. During the next 200 years, a vast body of knowledge concerning the properties of elements and their compounds was acquired by chemists. By 1869, a total of 63 elements had been discovered. As the number of known elements grew, scientists began to recognize patterns in properties and began to develop classification schemes.
Triads:-
In 1817 Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties. In 1829, after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium he proposed that nature contained triads of elements the middle element had properties that were an average of the other two members when ordered by the atomic weight (the Law of Triads).
First Flight Towards Designing Periodic Table :-
De Chancourtois transcribed a list of the elements positioned on a cylinder in terms of increasing atomic weight. When the cylinder was constructed so that 16 mass units could be written on the cylinder per turn, closely related elements were lined up vertically. This led De Chancourtois to propose that "the properties of the elements are the properties of numbers." De Chancourtois was first to recognize that elemental properties reoccur every seven elements, and using this chart, he was able to predict the the stoichiometry of several metallic oxides. Unfortunately, his chart included some ions and compounds in addition to elements.
Law of Octaves:-
John Newlands, an English chemist, wrote a paper in 1863 which classified the 56 established elements into 11 groups based on similar physical properties, noting that many pairs of similar elements existed which differed by some multiple of eight in atomic weight. In 1864 Newlands published his version of the periodic table and proposed the Law of Octaves (by analogy with the seven intervals of the musical scale). This law stated that any given element will exhibit analogous behavior to the eighth element following it in the table.
Elements In Family Order:-
A year earlier (1864) Lothar Meyer published a periodic table which described the placement of 28 elements. Meyer's periodic table ordered the elements into groups arranged in order of their atomic weights. His periodic table arranged the elements into 6 families according to their valence, which was the first attempt to classify the elements according to this property.
John Newlands, an English chemist, wrote a paper in 1863 which classified the 56 established elements into 11 groups based on similar physical properties, noting that many pairs of similar elements existed which differed by some multiple of eight in atomic weight. In 1864 Newlands published his version of the periodic table and proposed the Law of Octaves (by analogy with the seven intervals of the musical scale). This law stated that any given element will exhibit analogous behavior to the eighth element following it in the table.
Elements In Family Order:-
A year earlier (1864) Lothar Meyer published a periodic table which described the placement of 28 elements. Meyer's periodic table ordered the elements into groups arranged in order of their atomic weights. His periodic table arranged the elements into 6 families according to their valence, which was the first attempt to classify the elements according to this property.
In 1869, Lothar Meyer compiled a Periodic Table of 56 elements based on the periodicity of properties such as molar volume when arranged in order of atomic weight. Both Meyer and Mendeleev constructed periodic tables independently that are credited as being the basis of the modern table. Meyer was more impressed by the periodicity of physical properties, while Mendeleev was more interested in the chemical properties.
Mendeleev's Table Order:-
Mendeleev's Table Order:-
Mendeleev also published his periodic table & law in 1869, but he also forecast the properties of missing elements, and chemists began to appreciate it when, soon after, the discovery of elements predicted by gaps in his table took place.
"...if all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained."
"...if all the elements be arranged in order of their atomic weights a periodic repetition of properties is obtained."
This is known as Periodic Law and was stated by Mendleev
The periodic law, however, appears to have been independently formulated by at least six people within one decade - De Chancourtois, Newlands, Lothar Meyer, Mendeleev, Hinrichs, and Odling. Periodic tables have always been related to the way scientists thought about the shape and structure of the atom, and the relationships between elements, so has changed accordingly over time.
The periodic law, however, appears to have been independently formulated by at least six people within one decade - De Chancourtois, Newlands, Lothar Meyer, Mendeleev, Hinrichs, and Odling. Periodic tables have always been related to the way scientists thought about the shape and structure of the atom, and the relationships between elements, so has changed accordingly over time.
1894 Ramsay isolated Argon, and in the next year discovered helium. He went on to discover neon, krypton and xenon, and added a group to the periodic table to be called the Noble Gases - elements least likely to associate with others.
Later, the table was reordered by Mosely according to atomic numbers (nuclear charge) rather than by weight, thereby modifying the Periodic Law.
The Periodic Law revealed important analogies among the 94 naturally occurring elements, and stimulated renewed interest in Inorganic Chemistry in the nineteenth century which has carried into the present with the creation of artificially produced, short lived elements of `atom smashers' and supercolliders of high energy physics.
Harry D. Hubbard, of the United States National Bureau of Standards, modernized Mendeleev'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, 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.
Several scientists - and (me) a science exhibit designer - have revived the Chancourtois 3-D periodic table concept in the 20th Century. Some have started with a ribbon of elements in atomic number sequence and wrapped it in a spiral to vertically align elements with similar properties, which establishes the ‘periodic’ nature of the table. Others may have merely wrapped the plane of the flat table - after ramping the element rows – escalator-like – in the p-block - and let the post Emile/Dmitri element blocks loop to allow a perfect atomic number sequence. Some may have been seeking to resolve technical questions, and others, like Courtines, Gamov and Alexander, aiming for a better educational tool.
When Seaborg was shown the 1965 Alexander Arrangement in 1997, he said that it was 'correct', and later told a photographer that it was his 'favorite' periodic table. This arrangement retains the separate Lanthanide and Actinide series, but re-integrates them at the same time, a possibility only by using all three dimensions to produce a gap-free table.
The periodic table has been improved continuously over the last century and a half, built on the shoulders of many creative scientists.
The newer versions improve the educational possibilities by making possible element number continuity, easing both use & understanding of the immense correlative power of the periodic chart in teaching, learning, and working with chemistry.
Later, the table was reordered by Mosely according to atomic numbers (nuclear charge) rather than by weight, thereby modifying the Periodic Law.
The Periodic Law revealed important analogies among the 94 naturally occurring elements, and stimulated renewed interest in Inorganic Chemistry in the nineteenth century which has carried into the present with the creation of artificially produced, short lived elements of `atom smashers' and supercolliders of high energy physics.
Harry D. Hubbard, of the United States National Bureau of Standards, modernized Mendeleev'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, 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.
Several scientists - and (me) a science exhibit designer - have revived the Chancourtois 3-D periodic table concept in the 20th Century. Some have started with a ribbon of elements in atomic number sequence and wrapped it in a spiral to vertically align elements with similar properties, which establishes the ‘periodic’ nature of the table. Others may have merely wrapped the plane of the flat table - after ramping the element rows – escalator-like – in the p-block - and let the post Emile/Dmitri element blocks loop to allow a perfect atomic number sequence. Some may have been seeking to resolve technical questions, and others, like Courtines, Gamov and Alexander, aiming for a better educational tool.
When Seaborg was shown the 1965 Alexander Arrangement in 1997, he said that it was 'correct', and later told a photographer that it was his 'favorite' periodic table. This arrangement retains the separate Lanthanide and Actinide series, but re-integrates them at the same time, a possibility only by using all three dimensions to produce a gap-free table.
The periodic table has been improved continuously over the last century and a half, built on the shoulders of many creative scientists.
The newer versions improve the educational possibilities by making possible element number continuity, easing both use & understanding of the immense correlative power of the periodic chart in teaching, learning, and working with chemistry.
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