large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_210
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
Disregarding this, chemists clung to a standard atomic weight of 16.000 for oxygen as it appeared in nature, preferring not to concern themselves with the separate isotopes. DISREGARDING THIS CHEMISTS CLUNG TO A STANDARD ATOMIC WEIGHT OF SIXTEEN POINT ZERO ZERO FOR OXYGEN AS IT APPEARED IN NATURE PREFERRING NOT TO CONCERN THEMSELVES WITH THE SEPARATE ISOTOPES
_Harold Urey_] Even hydrogen does not escape. Its atomic weight is just about 1 and most of its atoms are ¹H. The American chemist Harold Clayton Urey (1893- ) detected the existence of a more massive isotope, ²H. This isotope has almost twice the mass of the lighter one. No other isotopes of a particular atom differ in mass by so large a factor. For that reason ²H and ¹H differ in ordinary chemical properties more than isotopes usually do and Urey therefore gave ²H the special name of “deuterium” from a Greek word meaning “second”. [Illustration: _W. F. Giauque_] In 1929 the American chemist William Francis Giauque (1895- ) found that oxygen was composed of more than 1 isotope. Its atomic weight had been set arbitrarily at 16.0000 so it was a relief that 99.76% of its atoms were ¹⁶O. However, 0.20% were ¹⁸O, and 0.04% were ¹⁷O. As you see, ¹⁶O must have a mass number of slightly less than 16.0000 and it must be the more massive isotopes ¹⁷O and ¹⁸O that pull the average up to 16.0000. ROGEN TWO THIS ISOTOPE HAS ALMOST TWICE THE MASS OF THE LIGHTER ONE NO OTHER ISOTOPES OF A PARTICULAR ATOM DIFFER IN MASS BY SO LARGE A FACTOR FOR THAT REASON HYDROGEN TWO AND HYDROGEN ONE DIFFER IN ORDINARY CHEMICAL PROPERTIES MORE THAN ISOTOPES USUALLY DO AND UREE THEREFORE GAVE HYDROGEN TWO THE SPECIAL NAME OF DETERIUM FROM A GREEK WORD MEANING SECOND IN NINETEEN TWENTY NINE THE AMERICAN CHEMIST WILLIAM FRANCIS GIAE BORN EIGHTEEN NINETY FIVE FOUND THAT OXYGEN WAS COMPOSED OF MORE THAN ONE ISOTOPE ITS ATOMIC WEIGHT HAD BEEN SET ARBITRARILY AT SIXTEEN EXACTLY SO IT WAS A RELIEF THAT NINETY NINE POINT SEVEN SIX PER CENT OF ITS ATOMS WERE OXYGEN SIXTEEN HOWEVER ZERO POINT TWO ZERO PER CENT WERE OXYGEN EIGHTEEN AND ZERO POINT ZERO FOUR PER CENT WERE OXYGEN SEVENTEEN AS YOU SEE OXYGEN SIXTEEN MUST HAVE A MASS NUMBER OF SLIGHTLY LESS THAN SIXTEEN POINT ZERO ZERO AND IT MUST BE THE MORE MASSIVE ISOTOPES OXYGEN SEVENTEEN AND OXYGEN EIGHTEEN THAT PULL THE AVERAGE UP TO SIXTEEN POINT ZERO ZERO
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