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CHEMISTRY: I, LANGMUIR 
atom of nickel are placed in the polar axis. Beyond nickel the electrons in 
the atom cannot be held by magnetic forces, and thus tend to rearrange them- 
selves so as to be placed as far as possible from the underlying electrons. This 
leads to an explanation of the chemical and magnetic properties of copper, 
zinc, etc. 
Krypton has in its third shell nine electrons in each hemisphere, symmetri- 
cally placed with respect to the polar axis and to the four electrons in the second 
shell. The ninth electron in each hemisphere goes into the polar axis. Xenon 
is like krypton, except that it has twice as many electrons in its third shell. 
Beyond Xenon eighteen electrons in the fourth shell can be held by magnetic 
forces over the eighteen cells of the third shell, so that lutecium, the eighteenth 
element beyond Xenon marks the last of the rare earth elements. The elec- 
trons in the outside shell of the atoms beyond this element are arranged as far 
as possible so as to leave eighteen empty spaces over the underlying electrons. 
In this way it is possible to explain the chemical and magnetic properties of 
tantallum and tungsten as contrasted to those of the rare earths. 
Niton has sixteen electrons in each hemisphere of its fourth shell. These 
are placed symmetrically with respect to the polar axis and the eight underly- 
ing electrons. 
This theory of atomic structure explains in a satisfactory way most of the 
periodic properties of all the elements including those of the eighth group and 
the rare earths. It lends itself especially well to the explanation of the so- 
called physical properties, such as boiling-points, freezing-points, electric con- 
ductivity, etc. For the details of its application to specific elements the paper 
in the Journal of the American Chemical Society should be consulted. 
Postulates 6, 7 and 8 lead directly to a new theory of valence which we may 
call the Octet Theory. This theory may be stated in terms of the equation 
e= Sn- 2p (1) 
where e is the total number of available electrons in the shells of all the atoms 
in a molecule; n is the number of octets forming the outside shells of the atoms 
and p is the number of pairs of electrons held in common by the octets (Pos- 
tulate 8). If we let E be the number of electrons in the 'shell' of an atom then 
e = 2 (£). The value of E for a given atom, at least in case of the first twenty 
elements, corresponds to the ordinal number of its group in the periodic table. 
Thus we have the following values of E: — one for hydrogen, Hthium, sodium, 
etc., two for magnesium, three for boron, aluminum, etc.; four for carbon and 
silicon, five for nitrogen and phosphorus; six for oxygen and sulphur; seven 
for the halogens, and zero for the inert gases. 
The above equation expresses the fact that every pair of electrons held in 
common between two octets results in a decrease in two in the total number of 
electrons needed to form the shells of the atoms in the molecules. It also im- 
plicitly expresses the fact that all the electrons in the shells of the atoms forming 
a molecule form part of one or two of the octets in the molecule. 
