aqa chemistry unit 3 history of the periodic table

History of the periodic table

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Timeline of the development of the periodic table
Scientist How did he develop the periodic table??
John He formulated one of the earliest attempts to classify the elements, by finding that some elements
Wolfgang grouped in threes that had related properties. He called these groups triads some of these triads are:
Doberiener Chlorine, bromine and iodine
1829 Calcium, strontium and barium
Lithium, sodium and potassium
In all of these triads the atomic weight of the second element was almost exactly the average of the
atomic weights of the third and first elements.
Dalton published a table of atomic weights in which six elements appear in this table: hydrogen,
John Dalton oxygen, nitrogen, carbon, sulphur and phosphorus. Dalton was convinced all gases were made and
1830 used the results of chemical analysis to prove this. His idea was that chemical combination takes
places between particles of different weights which were different from historic theories by the
Greeks. He also extended his idea to substances. He listed compounds as binary, ternary, quaternary
etc in the new system of chemical Philosophy depending on the number of atoms a compound had
in its simplest empirical form. Dalton used his own symbols to represent compounds in their atomic
structure. He believed atoms could not be created, destroyed or divided into smaller particles.
Alexandre-E Chancourtois was the first person to notice the periodicity of the element which is when similar
mile elements seem to occur at regular intervals when they are ordered by their atomic weights. He
Béguyer de devised an early form of the periodic table which was called the telluric helix. The elements were
arranged in a spiral on a cylinder in order of increasing atomic weight; Chancourtois saw that
elements with similar properties lined up vertically. His chart included some ions and compound in
s addition to elements. However his published paper did not include a diagram and used geological
1862 terms which meant it had little attention.
John John Newlands arranged the 56 known elements in order of atomic weights and observed similarities
Newlands between the first and ninth elements, the second and tenth. He proposed the law of octaves which
1964 identified many similarities amongst the elements, but also required similarities where none existed.
He did not leave spaces for elements as yet discovered. He was the first to assign atomic numbers
to elements however his work was rejected by his peers and the journal of the chemical society.
Newlands forced certain elements to fit his pattern creating mistakes e.g. elements with the different
properties in the same group
Dmitri Medeleev arranged the elements in a table ordered by atomic weight corresponding to their molar
Medeleev mass. Elements which are similar in regards to their properties have atomic weights which are nearly
1896 of the same value or increase regularly (K, Rb, Cs). The elements which are the most widely diffused
have small atomic weights. Certain properties can be found from their atomic weights. Medeleev
predicted further discoveries of other elements and left space for these new elements so there was
no disturbance in the table. However his table did not include any of the noble gases which were
discovered later and there was no place for the isotopes of various elements. Medeleev also
[pointed out that some of the then atomic weights were incorrect. John Meyer also discovered and
created a fairly similar table to that of Mendeleev's months before however his table only included
28 elements and the table was in order of valance not atomic weight.
William William Ramsey discovered the Nobel gases and entered them onto the periodic table. In 1894
Ramsey Ramsay removed oxygen, nitrogen, water and carbon dioxide from a sample of air and was left with
1894 a gas 19 times heavier than hydrogen, very un-reactive and with an unknown emission spectrum. He
called this gas Argon. In 1895 he discovered helium as a decay product of uranium and matched it to
the emission spectrum of an unknown element in the sun that was discovered in 1868. He went on
to discover neon, krypton and xenon, and realised these represented a new group in the Periodic

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Timeline of the development of the periodic table
Henry Henry Moseley found a relationship between an elements x-ray wavelength and it atomic number,
Moseley so he re-sequenced the table by nuclear charge rather than atomic weight. Moseley discovery
1914 showed that atomic numbers had a measurable basis, this new order he created agreed with the
chemical properties of the elements e.g. he placed argon before potassium based of x-ray
wavelength which worked because argon is a noble gas and potassium is an alkali metal.…read more


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