Today’s periodic table. Offnfopt/Wikipedia. But once you give Mendeleev’s table a 90-degree turn, the similarity to the modern version becomes apparent. For example, the halogens – fluorine (F), ...

By the periodic table’s logic, all d-block elements should have filled s orbitals. But copper defies that logic. It should have the electron configuration [Ar] 3d 9 4s 2 .

Iodine is classified as a halogen — a subset of very chemically reactive elements (Group 17 on the periodic table) that exist in the environment as compounds rather than as pure elements.

The periodic table is not just the story of discoveries aided by better technological innovations, ... The classic example is of iodine (atomic mass 126.9) and tellurium (127.6).

150 years ago, Russian chemist Dmitrii Mendeleev created the periodic table of the elements, ... Bromine, for example, had an atomic weight midway between the weights of chlorine and iodine, ...

Predictive power. Gallium. Mendeleev left blank spaces in his original periodic table so that he could properly line up the known elements. Gallium, element 31, was his first gap to be filled, in ...

The periodic table stares down from the walls of just about every chemistry lab. The credit for its creation generally goes to Dimitri Mendeleev, a Russian chemist who in 1869 wrote out the known ...