The periodic table of elements, devised by Russian chemist Dmitri Mendeleev, is a two-dimensional array of the chemical elements, ordered by atomic number and arranged 18 across by orbitals.

Periodic Puzzler Help This puzzle shows many of the elements used to make transistors. The finished puzzle is a section of the periodic table, so the numbers on each tile are their atomic numbers ...

On rationalising the periodic table, the NCERT said that discussion about basic concepts such as elements, symbols, and formation of compounds, atoms and molecules had been dealt with in Class 9.

This article was originally published with the title “ The Periodic Table of the Cosmos: 100 Years of the Hertzsprung-Russell Diagram ” in Scientific American Magazine Vol. 305 No. 1 (July ...