dmitri mendeleev organized the periodic table by atomic number.
dmitri mendeleev organized the periodic table by atomic number.
who organized the periodic table by atomic number?
dmitri mendeleev
in addition, moseley showed that there were gaps in the atomic number sequence at numbers 43, 61, 72, and 75. these spaces are now known, respectively, to be the places of the radioactive synthetic elements technetium and promethium, and also the last two quite rare naturally occurring stable elements hafnium (discovered 1923) and rhenium (discovered 1925). nothing was known about these four elements in moseley's lifetime, not even their very existence. based on the intuition of a very experienced chemist, dmitri mendeleev had predicted the existence of a missing element in the periodic table, which was later found to be filled by technetium, and bohuslav brauner had predicted the existence of another missing element in this table, which was later found to be filled by promethium. henry moseley's experiments confirmed these predictions, by showing exactly what the missing atomic numbers were, 43 and 61. in addition, moseley predicted the existence of two more undiscovered elements, those with the atomic numbers 72 and 75, and gave very strong evidence that there were no other gaps in the periodic table between the elements aluminium (atomic number 13) and gold (atomic number 79).
henry moseley
following the discovery of the atomic nucleus by ernest rutherford in 1911, it was proposed that the integer count of the nuclear charge is identical to the sequential place of each element in the periodic table. in 1913, henry moseley using x-ray spectroscopy confirmed this proposal experimentally. moseley determined the value of the nuclear charge of each element and showed that mendeleev's ordering actually places the elements in sequential order by nuclear charge. nuclear charge is identical to proton count and determines the value of the atomic number ("z") of each element. using atomic number gives a definitive, integer-based sequence for the elements. moseley predicted, in 1913, that the only elements still missing between aluminium ("z" = 13) and gold ("z" = 79) were "z" = 43, 61, 72, and 75, all of which were later discovered. the atomic number is the absolute definition of an element and gives a factual basis for the ordering of the periodic table. in other words, since the atomic number of an element is the same as the number of protons in its nucleus, the modern periodic table arranges the elements according to their atomic number, and relative to their atomic mass, the way mendeleev did. the periodic table is used to predict the properties of new synthetic elements before they are produced and studied.
periodic table