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Lavoisier
Born in 1770, Lavoiosier was the first person to construct a list of elements. The list consisted on 33 substances which he could not break down into smaller substances and also distinguished between metals and non-metals. Some of the elements were later found to be compounds or mixtures. Antoine Lavoisier wrote the first list of elements containing 33 elements. The list of elements included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc and sulphur, which formed the basis for the mode -
Dobereiner
Between 1817-1829 Johann Dobereiner developed the triads which were groups of 3 elements with similar properties. For example: sodium, lithium and potassium formed a triad. Calcium, strontium and barium formed a triad, chlorine, bromine and iodine also formed a triad. Döbereiner tried to group elements in the periodic table, but found that some elements, can be grouped into threes, hence the name “Döbereiner’s Triads”. The elements Nitrogen, Phosphorous, and Arsenic can be grouped together usin -
Newlands
In 1863, John Newlands, an English chemist, proposed the Law of Octaves which stated that elements repeated their chemical properties every eighth element.The musical analogy was ridiculed at the time, but was found to be insightful after the work of Mendeleev and Meyer were published.
In 1864, he noticed that, if the elements were arranged in order of atomic weight, there was a periodic similarity every 8 elements. He proposed his ‘law of octaves’ on this.
He arranged all the elements known at -
Meyer
In 1864 Meyer produced a table of just 28 elements which he listed by their valence. The term valence is now called valency and represents 'combining power' of an element
Eg. Sodium forms a chloride NACl and has a valency of 1
The 28 elements were almost entirely main group elements
1868 - Incorporated transition metals in another table Listed the elements in increasing weight order with elements with the same valence in a given column
This was earlier than Mendeleev's table (1869) but unfort -
Mendeleev
With the help of a set of cards Mendeleev organised and rearranged materials until patterns became evident. After rearranging the cards several times, he discovered that similarities and chemical behaviour occurred regularly when he placed them in order of increasing atomic mass. In 1869 Russian scientist Russian chemist and teacher Dmitri Mendeleev published the first periodic table.
He is generally given more credit than Meyer who published a similar table slightly after Mendeleev because hi -
Seaborg
The elements he discovered all have an atomic number higher than 92 (Uranium) and are man-made. He also discovered the fact that uranium could be hit with neutrons to create new elements. This led to the expansion of the periodic table. The elements had already been discovered by chemists, as they existed on Earth already mostly combined with other elements as compounds. The elements he and his co-workers discovered were created in their lab, as they do not occur in pure form naturally.
