large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_253
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
It is not surprising that the atomic weights of nitrogen and carbon are just about 14 and 12, respectively. IT IS NOT SURPRISING THAT THE ATOMIC WEIGHTS OF NITROGEN AND CARBON ARE JUST ABOUT FOURTEEN AND TWELVE
 close to a whole number to begin with, it may consist of a single kind of atom. For instance, the gas fluorine (chemical symbol F) has an atomic weight of nearly 19, while that of the metal sodium (chemical symbol Na) is nearly 23. As it turns out, all the atoms of fluorine are of the single variety ¹⁹F, while all the atoms of sodium are ²³Na. Sometimes the atomic weight of an element, as it occurs in nature, is nearly a whole number and yet it is made up of more than 1 isotope. In that case, one of the isotopes makes up very nearly all of it, while the others are present in such minor quantities that the average is hardly affected. Helium, for instance (atomic symbol He) has an atomic weight of just about 4 and, indeed, almost all the atoms making it up are ⁴He. However, 0.0001% of the atoms, or one out of a million, are ³He. Again, 99.6% of all the nitrogen atoms (atomic symbol N) are ¹⁴N, but 0.4% are ¹⁵N. Then, 98.9% of all carbon atoms (atomic symbol C) are ¹²C, but 1.1% are ¹³C. UM CHEMICAL SYMBOL N A IS NEARLY TWENTY THREE AS IT TURNS OUT ALL OF THE ATOMS OF FLOORIN ARE OF THE SINGLE VARIETY FLORINE NINETEEN WHILE ALL THE ATOMS OF SODIUM ARE SODIUM TWENTY THREE SOMETIMES THE ATOMIC WEIGHT OF AN ELEMENT AS IT OCCURS IN NATURE IS NEARLY A WHOLE NUMBER AND YET IT IS MADE UP OF MORE THAN ONE ISOTOPE IN THAT CASE ONE OF THE ISOTOPES MAKE UP VERY NEARLY ALL OF IT WHILE THE OTHERS ARE PRESENT IN SUCH MINOR QUANTITIES THAT THE AVERAGE IS HARDLY AFFECTED HELIUM FOR INSTANCE ATOMIC SYMBOL H E HAS AN ATOMIC WEIGHT OF JUST ABOUT FOUR AND INDEED ALMOST ALL THE ATOMS MAKING IT UP ARE HELIUM FOUR HOWEVER ONE ONE THOUSANDTH OF ONE PER CENT OF THE ATOMS OR ONE OUT OF A MILLION R HELIUM THREE AGAIN NINETY NINE POINT SIX PER CENT OF ALL THE NITROGEN ATOMS ATOMIC SYMBOL N ARE NITROGEN FOURTEEN BUT ZERO POINT FOUR PER CENT ARE NITROGEN FIFTEEN THEN NINETY EIGHT POINT NINE PER CENT OF ALL CARBON ATOMS ATOMIC SYMBOL C ARE CARBON TWELVE BUT ONE POINT ONE PER CENT ARE CARBON THIRTEEN
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