large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_233
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
_] The Danish physicist Niels Bohr (1885 1962) had just advanced a theory of atomic structure that made it reasonable to suppose that the wavelength of the characteristic X rays depended on the size of the nuclear charge of the atoms making up a particular element. TEEN SIXTY TWO HAD JUST ADVANCED A THEORY OF ATOMIC STRUCTURE THAT MADE IT REASONABLE TO SUPPOSE THAT THE WAVE LENGTH OF THE CHARACTERISTIC X RAYS DEPENDED ON THE SIZE OF THE NUCLEAR CHARGE OF THE ATOMS MAKING UP A PARTICULAR ELEMENT
oseley found that the greater the atomic weight of an atom, the shorter the waves of the characteristic X rays associated with it and the more penetrating those X rays were. There was such a close connection, in fact, that Moseley could arrange the elements in order according to the wavelength of the characteristic X rays. For some 40 years prior to this, the elements had been listed in order of atomic weight. This was useful especially since the Russian chemist Dmitri I. Mendeléev (1834-1907) had arranged them in a “periodic table” based on the atomic weight order in such a way that elements of similar properties were grouped together. The elements in this table were sometimes numbered consecutively (“atomic number”) but this was inconvenient since, when new elements were discovered, the list of atomic numbers might have to be reorganized. [Illustration: _Dmitri Mendeléev and Bohuslav Brauner in Prague in 1900. Brauner was a professor of chemistry at the Bohemian University in Prague. NT FROM THE DEGREE OF BENDING THE WAVE LENGTH OF THE WAVES CAN BE DETERMINED MOSELY FOUND THAT THE GREATER THE ATOMIC WEIGHT OF AN ATOM THE SHORTER THE WAVES OF THE CHARACTERISTIC X RAYS ASSOCIATED WITH IT AND THE MORE PENETRATING THOSE X RAYS WERE THERE WAS SUCH A CLOSE CONNECTION IN FACT THAT MOSELY COULD ARRANGE THE ELEMENTS IN ORDER ACCORDING TO THE WAVE LENGTH OF THE CHARACTERISTIC X RAYS FOR SOME FORTY YEARS PRIOR TO THIS THE ELEMENTS HAD BEEN LISTED IN ORDER OF ATOMIC WEIGHT THIS WAS USEFUL ESPECIALLY SINCE THE RUSSIAN CHEMIST DMITRI EI MENDELIEV EIGHTEEN THIRTY FOUR TO NINETEEN O SEVEN HAD ARRANGED THEM IN A PERIODIC TABLE BASED ON THE ATOMIC WEIGHT ORDER IN SUCH A WAY THAT ELEMENTS OF SIMILAR PROPERTIES WERE GROUPED TOGETHER THE ELEMENTS IN THIS TABLE WERE SOMETIMES NUMBERED CONSECUTIVELY ATOMIC NUMBER BUT THIS WAS INCONVENIENT SINCE WHEN NEW ELEMENTS WERE DISCOVERED THE LIST OF ATOMIC NUMBERS MIGHT HAVE TO BE REORGANIZED THE DANISH PHYSICIST NEILSBOR EIGHTEEN EIGHTY FIVE NINE
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