large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_139
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
The atomic number increases as one goes up the line of atoms. Oxygen atoms, for instance, have an atomic number of 8 and iron atoms have one of 26. At the upper end, thorium is 90 and uranium is 92. Each uranium atom has a nucleus bearing a charge of +92 and contains 92 electrons to balance this. THE ATOMIC NUMBER INCREASES AS ONE GOES UP THE LINE OF ATOMS OXYGEN ATOMS FOR INSTANCE HAVE AN ATOMIC NUMBER OF EIGHT AND IRON ATOMS HAVE ONE OF TWENTY SIX AT THE UPPER END THORIUM IS NINETY AND URANIUM IS NINETY TWO EACH ERRANIUM ATOM HAS A NUCLEUS BEARING A CHAR OF PLUS NINETY TWO AND CONTAINS NINETY TWO ELECTRONS TO BALANCE THIS
ation: _Dmitri Mendeléev and Bohuslav Brauner in Prague in 1900. Brauner was a professor of chemistry at the Bohemian University in Prague._] 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. Moseley therefore suggested that these X rays be used to determine the size of the positive charge on its nucleus. The atomic number could then be set equal to that charge and be made independent of new discoveries of elements. Hydrogen, for instance, has an atomic number of 1. Its nucleus carries a unit positive charge, +1, and the hydrogen atom possesses 1 electron to balance this. Helium, with an atomic number of 2, has a nuclear charge of +2 and 2 electrons, with a total charge of -2, to balance it. (The alpha particle released by radioactive atoms is identical with a helium nucleus.) ENIENT SINCE WHEN NEW ELEMENTS WERE DISCOVERED THE LIST OF ATOMIC NUMBERS MIGHT HAVE TO BE REORGANIZED THE DANISH PHYSICIST NEILSBOR EIGHTEEN EIGHTY FIVE NINETEEN 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 MOSELY THEREFORE SUGGESTED THAT THESE X RAYS BE USED TO DETERMINE THE SIZE OF THE POSITIVE CHARGE ON ITS NUCLEUS THE ATOMIC NUMBER COULD THEN BE SET EQUAL TO THAT CHARGE AND BE MADE INDEPENDENT OF NEW DISCOVERIES OF ELEMENTS HYDROGEN FOR INSTANCE HAS AN ATOMIC NUMBER OF ONE ITS NUCLEUS CARRIES A UNIT POSITIVE CHARGE PLUS ONE AND THE HYDROGEN ATOM POSSESSES ONE ELECTRON TO BALANCE THIS HELIUM WITH AN ATOMIC NUMBER OF TWO HAS A NUCLEAR CHARGE OF PLUS TWO AND TWO ELECTRONS WITH A TOTAL CHARGE OF MINUS TWO TO TO BALANCE IT THE ALPHA PARTICLE RELEASED BY RADIOACTIVE ATOMS IS IDENTICAL WITH A HELIUM NUCLEUS
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