7-8 February 22

Dmitri Mendeleev, the "father" of the modern periodic table of the elements, was born in Russia on 8 February 1839. So I'm wearing my periodic table tie for him. Yesterday, 7 February, is sometimes celebrated as Periodic Table Day, marking the 1863 publication of one of the first tables of elements, by English chemist John Newlands. Mendeleev released his table six years later, apparently unaware of what Newlands had produced. Both of them expressed the general pattern that the elements, when arranged in order of their atomic weights, show remarkable similarities if you pair them by eights (the first one and the eighth one, and the second one and ninth one, and so on). Although our periodic table today has many more elements than either Newlands or Mendeleev knew, its design still shows the close resemblances of sodium-and-potassium and carbon-and-silicon and oxygen-and-sulfur and so on (the vertical "groups").