7 4 THE QUANTUM [ v . 3 
the periodic properties of the elements on the basis of the stability 
of such configurations. " Although Thomson’s assumption re 
garding the distribution of the positive electricity in the atom is 
not consistent with more recent experimental evidence, never 
theless his work has exerted great influence upon the later 
developments of the atomic theory on account of the many 
original ideas which it contained ” (Bohr). 
The atomic model now generally accepted supposes that the 
resultant positive charge is concentrated in an extremely minute 
nucleus which is surrounded by the negative electrons. In 
1904 Professor Nagaoka discussed an atomic model of this kind, 
which may be termed a saturnian atom. He imagined an 
attracting centre and a large number of equal particles repelling 
one another inversely as the square of the distance moving 
round the circumference of the circle. Very similar is the 
“ nuclear atom ” developed by Sir Ernest Rutherford in 1911. It 
is to Rutherford that we owe the experimental evidence in favour 
of this model, for he showed that the positive charge is con 
centrated in a nucleus of extremely small dimensions, containing 
practically the whole mass of the atom, whilst electrons are 
arranged round about the nucleus in certain orbits or in certain 
definite rings. 
The theory developed by Bohr on the basis of the old quantum 
theory makes use of this atomic model, and a particular electron 
is supposed to describe an orbit which may be specified by 
one or more quantum numbers. Kossel on the one hand, and 
Lewis and Langmuir on the other, have emphasized the fact 
that in the periodic system there are certain elements which 
must correspond to especially stable configurations of electrons. 
These are the inactive gases helium, neon, argon, krypton, xenon 
and niton (radon). 
Table of Electron Configurations 
Langmuir. 
Element. 
Bohr. 
2 
2 8 
288 
2 8 8 18 
2 8 8 18 18 
2 8 8 18 18 32 
Helium 
Neon 
Argon 
Krypton 
Xenon 
Niton 
2i 
2i 8 2 
2j 8 2 83 
2i 8 2 183 8 4 
2j 8 2 183 I84 8 5 
2 X 8 2 183 324 185 8 6 
The small subscript figures which appear on the right indicate 
the character of the orbit in Bohr’s theory. It will be noticed