History of Periodic Table

Chemistry (Salters)

Open-Book Paper 14 February 2004

German chemist Johann Dobereiner was the first to attempt to classify elements using their atomic weights (now known as relative atomic mass). He identified triads in the list of elements, for each triad the atomic weight of the middle element was approximately the average of the other two.

In 1863, John Newlands noted that when the elements were written in order of increasing atomic weight, every eighth element had similar properties. So Newlands tried to produce a new periodic table based on his discovery but after about 20 elements his table became ragged; he had to put two elements in one space and some elements were in the wrong place because Newlands used inaccurately measured atomic weights. Still, Newlands was quite close to the right answer.

The Modern Periodic Table

The Modern periodic table is closely based on Mendeleev’s table. All the gaps that he left have been filled as more and more new elements were discovered. A new group was established for the noble gases. Also the elements are now arranged in order of increasing atomic number, instead of atomic weight.

Gallium and Mendeleev’s Theory about Periodic Table

Mendeleev unlike previous scientists did not only produce a periodic table based on the elements that had been discovered at that ...