There are about one hundred kinds of atom. Those heavier than radium
(atomic number 92) do not appear in nature, and, when created artificially,
have lifetimes which become shorter and shorter as the weight increases,
until it is only a fraction of
"The third kingdom, that of atoms, introduces the possibility of identification, of location in space, of clear definition. Here we have the atom: it is carbon, or oxygen, or sodium; we can locate it, tag it, and know its properties: In fact, thanks to the same quantum theory that denies complete knowledge of the proton and electron in the second kingdom, we have a complete explanation for the atom in the third kingdom. Not only does every atom (or element) have properties that can be completely explained by reference to the number of proton-electron pairs, called the atomic number, but the spectral lines radiated by the atom, which represent energy differences between orbits of electrons, can also be precisely accounted for.  the superbly rational properties of atoms are a characteristic we believe to be categorical, for,..., the level of this kingdom (level III) is that at which concept formation occurs; more simply, it is form itself."
Arthur M. Young, The Reflexive Universe, p.56
Table of Elements
 The frequency of the spectral lines is predictable, but when the atom will radiate is unpredictable. This is the one degree of freedom present at level III
Is the Atom Fundamental?
The quantum mechanical view of the atom
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