large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_234
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
Its atomic weight was 207.2. ITS ATOMIC WEIGHT WAS TWO
referred to as lead-206, lead-207, and lead-208. If we use the chemical symbol for lead (Pb), we could write the isotopes, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb. (We read the symbol ²⁰⁶Pb as lead-206.) Atomic weight measurements made in 1914 by Soddy and others supported that theory. All 3 lead isotopes had the same atomic number of 82. The atoms of all 3 isotopes had nuclei with an electric charge of +82 and all 3 had 82 electrons in the atom to balance that positive nuclear charge. The difference was in the mass of the nucleus only. [Illustration: _Isotopes of two elements._] Atomic number, 1 Hydrogen-1: Mass number, 1; 1 Proton, 1 Electron Hydrogen-2: Mass number, 2; 1 Proton, 1 Neutron, 1 Electron Atomic number, 2 Helium-3: Mass number, 3; 2 Protons, 1 Neutron, 2 Electrons Helium-4: Mass number, 4; 2 Protons, 2 Neutrons, 2 Electrons But what of ordinary lead that existed in the rocks far removed from any radioactive substances and that had presumably been stable through all the history of earth?  ATOMIC WEIGHT OF TWO O SEVEN IF THIS WERE SO THERE WOULD BE THREE LEAD ISOTOPES THAT WOULD DIFFER NOT IN RADIOACTIVE PROPERTIES BUT IN ATOMIC WEIGHT THE ISOTOPES COULD BE REFERRED TO AS LEAD TO O SIX LEAD TO O SEVEN AND LEAD TO O EIGHT IF WE USED THE CHEMICAL SYMBOL FOR LEAD P B WE WOULD WRITE THESE ISOTOPES SUPERSCRIPT TWO O SIX P SUPERSCRIPT TO O SEVEN B AND SUPERSCRIPT TO EIGHT B WE READ THE SYMBOL SUPERSCRIPT TWO O SIX B AS LEAD TWO O SIX ATOMIC WEIGHT MEASUREMENTS MADE IN NINETEEN FOURTEEN BY SODDI AND OTHERS SUPPORTED THAT THEORY ALL THREE LEAD ISOTOPES HAD THE SAME ATOMIC NUMBER OF EIGHTY TWO THE ATOMS OF ALL THREE ISOTOPES HAD NUCLEI WITH AN ELECTRIC CHARGE OF PLUS EIGHTY TWO AND ALL THREE HAD EIGHTY TWO ELECTRONS IN THE ATOM TO BALANCE THAT POSITIVE NUCLEAR CHARGE THE DIFFERENCE WAS IN THE MASS OF THE NUCLEUS ONLY BUT WHAT OF ORDINARY LEAD THAT EXISTED IN THE ROCKS FAR REMOVED FROM ANY RADIOACTIVE SUBSTANCES AND THAT HAD PRESUMABLY BEEN STABLE THROUGH ALL THE HISTORY OF EARTH
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