large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_216
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
It quickly turned out that the atomic number was more fundamental and more characteristic of a particular element than was the atomic weight. IT QUICKLY TURNED OUT THAT THE ATOMIC NUMBER WAS MORE FUNDAMENTAL AND MORE CHARACTERISTIC OF A PARTICULAR ELEMENT THAN WAS THE ATOMIC WEIGH
es 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.) 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. Once the notion of the atomic number was worked out, it became possible to tell for certain whether any elements remained as yet undiscovered and, if so, where in the list they might be. Thus, when Moseley first presented scientists with the atomic number it turned out that there were still 7 elements that were not discovered. At least elements with atomic numbers of 43, 61, 72, 75, 85, 87, and 91 were still not known. By 1945, all seven had been discovered. RONS WITH A TOTAL CHARGE OF MINUS TWO TO TO BALANCE IT THE ALPHA PARTICLE RELEASED BY RADIOACTIVE ATOMS IS IDENTICAL WITH A HELIUM NUCLEUS 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 ONCE THE NOTION OF THE ATOMIC NUMBER WAS WORKED OUT IT BECAME POSSIBLE TO TELL FOR CERTAIN WHETHER ANY ELEMENTS REMAINED AS YET UNDISCOVERED AND IF SO WHERE IN THE LIST THEY MIGHT BE THUS WHEN MOSELY FIRST PRESENTED SCIENTISTS WITH THE ATOMIC NUMBER IT TURNED OUT THAT THERE WERE STILL SEVEN ELEMENTS THAT WERE NOT DISCOVERED AT LEAST ELEMENTS WITH ATOMIC NUMBERS OF FORTY THREE SIXTY ONE SEVENTY TWO SEVENTY FIVE EIGHTY FIVE EIGHTY SEVEN AND NINETY ONE WERE STILL NOT KNOWN BY NINETEEN FORTY FIVE ALL SEVEN HAD BEEN DISCOVERED
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