Not a member?     Existing members login below:

Alchemy: Ancient and Modern


[5]
Or perhaps an isotope of helium (see below).
As concerns the spontaneous transmutations undergone by the radioactive
elements, the facts appear to indicate (or, at least, can be brought into some sort of
order by supposing) the atom to consist of a central nucleus and an outer shell, as
suggested by Sir Ernest Rutherford. The nucleus may be compared to the sun of a
solar system. It is excessively small, but in it the mass of the atom is almost entirely
concentrated. It is positively charged, the charge being neutralised by that of the
free electrons which revolve like planets about it, and which by the ir orbits account
for the
[viii]
volume of the atom. The atomic weight of the element depends upon the central
sun; but the chemical properties of the element are determined by the number of
electrons in the shell; this number is the same as that representing the position of
the element in the periodic system. Radioactive change originates in the atomic
nucleus. The expulsion of an a-particle therefrom decreases the atomic weight by 4
units, necessitates (since the a-particle carries two positive charges) the removal of
two electrons from the shell in order to maintain electrical neutrality, and hence
changes the chemical nature of the body, transmuting the element into one
occupying a position two places to the left in the periodic system (for example, the
change of radium into niton). But radioactivity sometimes results in the expulsion of
a ß-particle from the nucleus. This results in the addition of an electron to the shell,
and hence changes the chemical character of the element, transmuting it into one
occupying a position one place to the right in the periodic system, but without
altering its atomic weight. Consequently, the expulsion of one a- and two ß-particles
from the nucleus, whilst decreasing the atomic weight of the element by 4, leaves
the number of electrons in the shell, and thus the chemical properties of the
element, unaltered. These remarkable conclusions are amply borne out by the facts,
and the discovery of elements (called “isobares”) having the same atomic weight but
different chemical properties, and of those (called “isotopes”) having identical
chemical characters but different atomic weights, must be regarded as one of the
most significant and important discoveries of recent years. Some further reference
[ix]
to this theory will be found in §§ 77 and 81: the reader who wishes to follow the
matter further should consult the fourth edition of Professor Frederick Soddy’s The
Interpretation of Radium (1920), and the two chapters on the subject in his Science
and Life (1920), one of which is a popular exposition and the other a more technical
one.
These advances in knowledge all point to the possibility of effecting transmutations
at will, but so far attempts to achieve this, as I have already indicated, cannot be
regarded as altogether satisfactory. Several methods of making gold, or rather
elements chemically identical with gold, once the method of controlling radioactive
change is discovered (as assuredly it will be) are suggested by Sir Ernest
Rutherford’s theory of the nuclear atom. Thus, the expulsion of two a-particles from
bismuth or one from thallium would yield the required result. Or lead could be
Remove