360Mendeleev presents the periodic table of the elements
On 6 March 1869, the Russian chemist Dmitri Mendeleev's periodic table was presented to the Russian Chemical Society. He arranged the 63 known elements by atomic weight and grouped them by their properties, leaving gaps for elements not yet discovered. When gallium, scandium and germanium were found, they matched his predictions.
By the 1860s, chemists knew 63 elements but had no clear way to organise them. Dmitri Mendeleev, a professor in St Petersburg, was writing a chemistry textbook and wanted to make sense of them.
He listed the elements in order of atomic weight and noticed that similar properties repeated at regular intervals. He arranged them in a table so that elements with similar behaviour, such as lithium, sodium and potassium, fell into the same group.
His table was presented to the Russian Chemical Society on 6 March 1869. Its boldest feature was the gaps. Mendeleev said they belonged to elements still to be found, and he predicted their weights and properties.
He was proved right. Gallium was discovered in 1875, scandium in 1879 and germanium in 1886, each closely matching his predictions.
Later scientists found that the true order follows atomic number, the number of protons in each atom. Today's table holds 118 elements. Element 101, mendelevium, is named in his honour.
- 6 March 1869
- Mendeleev's table is presented
- 1875
- Gallium is discovered
- 1886
- Germanium is discovered
- 1955
- Element 101 is named mendelevium
Sources: Royal Society of Chemistry · Britannica · Science History Institute.