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Periodic table - OCR GatewayMendeleev鈥檚 periodic table

Mendeleev made an early periodic table. In the modern table, elements are put in order of atomic number into periods and groups. Electron arrangements model how electrons are arranged in atoms.

Part of Chemistry (Single Science)Elements, compounds and mixtures

Mendeleev鈥檚 periodic table

Dmitri Mendeleev

Dmitri Mendeleev (1834-1907) was a Russian chemist. In the 19th century, he was one of several scientists who were looking for ways to organise the known . Mendeleev published his first periodic table of the elements in 1869.

Learn more on the periodic table in this podcast.

Features of Mendeleev鈥檚 tables

Mendeleev arranged the elements in order of increasing . He then considered the of the elements and their . Mendeleev found that this allowed him to arrange elements with similar properties below each other into groups. However, to make this work, he had to:

  • leave gaps for yet to be discovered elements
  • swap the order of a few pairs of elements

Mendeleev鈥檚 1869 table showed groups of elements in horizontal rows, but from 1871 he showed groups of elements in vertical columns.

Six rows, eight columns showing H, Li, Be, B, C, N, O, F. Na, Mg, Al, Si, P, S, Cl, K,  Ca, Ti, V, Cr. Fe, Co, Ni and Cu. (Cu), Zn, As, So, B,  Rb, Sr, Yt, Zr, Nb, Mo, Ru. Rh, Pd and Ag.

Predictions using gaps

Mendeleev left gaps in his table to place elements not known at the time. By looking at the and of the elements next to a gap, he could also predict the properties of these undiscovered elements. For example, Mendeleev predicted the existence of 鈥榚ka-silicon鈥, which would fit into a gap next to silicon. The element germanium was discovered later. Its properties were found to be similar to the predicted ones, which supported the ideas behind Mendeleev鈥檚 periodic table.

Pair reversals

Iodine has a lower relative atomic mass than tellurium. So iodine should be placed before tellurium in Mendeleev鈥檚 tables. However, iodine has similar chemical properties to chlorine and bromine. To make iodine line up with chlorine and bromine in his table, Mendeleev swapped the positions of iodine and tellurium.