PRESENTATION OUTLINE
THE CONTRIBUTION OF EACH SCIENTIS IN THE PERIODIC TABLE
The contribution of Lavoisier, Chancourtois, Dobereiner, Newland, Mendelev, Ramsay, and Moseley.
The contribution of Lavoisier
Wrote the first extensive list of elements containing 33 elements. Distinguished between metals and non-metals.
The contribution of Chancourtois
In 1862, a year before John Alexander Reina Newlands published his classification of the elements, de Chancourtois created a fully functioning and unique system of organizing the chemical elements. His proposed classification of elements was based on the newest values of atomic weights obtained by Stanislao Cannizzaro in 1858. De Chancourtois devised a spiral graph that was arranged on a cylinder which he called vis tellurique, or telluric helix because tellurium was the element in the middle of the graph. De Chancourtois ordered the elements by increasing atomic weight and with similar elements lined up vertically.
The contribution of Dobereiner
Developed triads , groups of 3 elements with similar properties. Lithium, sodium and potassium formed a triad.
Calcium, strontium and barium formed a triad. Chlorine, bromine and iodine formed a triad.
The contribution of Newland
The known elements (>60) were arranged in order of atomic weights and observed similarities between the first and ninth elements, the second and tenth elements etc. He proposed the "Law of Octaves".
The contribution of Mendelev
Produced a table based on atomic weights but arranged 'periodically' with elements with similar properties under each other. Gaps were left for elements that were unknown at that time and their properties predicted (the elements were gallium, scandium and germanium). The order of elements was re-arranged if their properties dictated it, eg, tellerium is heavier than iodine but comes before it in the Periodic Table.
The contribution of Ramsay
Discovered the noble gases. In 1894 Ramsay removed oxygen, nitrogen, water and carbon dioxide from a sample of air and was left with a gas 19 times heavier than hydrogen, very unreactive 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. (helios is the Greek for Sun). He went on to discover neon, krypton and xenon, and realised these represented a new group in the Periodic Table. Ramsay was awarded a Nobel Prize in 1904.
The contribution of Moseley
Determined the atomic number of each of the elements.
He modified the 'Periodic Law' to read that the properties of the elements vary periodically with their atomic numbers. Moseley's modified Periodic Law puts the elements tellerium and iodine in the right order, as it does for argon and potassium, cobalt and nickel.
1914 Predicted that there were 3 unknown elements between aluminium and gold and concluded there were only 92 elements up to and including uranium.
