THE RELATION BETWEEN THE PROPERTIES AND ATOMIC WEIGHTS
OF THE ELEMENTS.
In undertaking to prepare a textbook called "Principles of Chemistry," I wished to establish
somesort of system of simple bodies in which their distribution is not guided by chance, as might
be thought instinctively, but by some sort of definite and exact principle. We previously saw that
there was an almost complete absence of numerical relations for establishing a system of simple
bodies, but in the end any system based on numbers which can be determined exactly will
deserve preference over other Systems which do not have numerical support, since the former
leave little room for arbitrary choices. The numerical data for simple bodies are limited at the
present time. If for some of them the physical properties are determined with certainty, yet this
applies only to a very small number of the elementary bodies. For example, such properties as
optical, or even electrical or magnetic, ones, cannot in the end serve as a support for a system
because one and the same body can show different values for these properties, depending on the
state in which they occur. In this regard, it is enough to recall graphite and diamond, ordinary
and red phosphorus, and oxygen and ozone. Not only do we not know the density in the vapour
state for most of them, by which to determine the weight of the particles of the simple bodies, but
this density is subject to alteration exactly like those polymeric alterations which have been
noted for complex bodies. Oxygen and sulphur show this effect positively, but the relations
between nitrogen, phosphorus, and arsenic offer further confirmation because these similar
elements have particle weights of N2, P4, and As4, unequal in the number of atoms among
themselves. A number of the properties of the simple bodies must change with these polymeric
changes. Thus we cannot be sure that for any element, even for platinum, there may not occur
another state, and the location of an element in a system based on its physical properties would
then be changed. Besides this, anyone understands that no matter how the properties of a simple
body may change in the free state, something remains constant, and when the elements form
compounds, this something has a material value and establishes the characteristics of the
compounds which include the given element. In this respect, we know only one constant peculiar
to an element, namely, the atomic weight. The size of the atomic weight, by the very essence of
the matter, is a number which is not related to the state of division of the simple body but to the
material part which is common to the simple body and all its compounds. The atomic weight
belongs not to coal or the diamond, but to carbon. The property which Gerhardt and Cannizzaro
determined as the atomic weight of the elements is based on such a firm and certain assumption
that for most bodies, especially for those simple bodies whose heat capacity in the free state has
been determined, there remains no doubt of the atomic weight, such as existed some years ago,
when the atomic weights were so often confused with the equivalents and determined on the
basis of varied and often contradictory ideas.
This is the reason I have chosen to base the system on the size of the atomic weights of the
elements.
The first attempt which I made in this way was the following: I selected the bodies with the
lowest atomic weights and arranged them in the order of the size of their atomic weights. This
showed that there existed a period in the properties of the simple bodies, and even in terms of
their atomicity the elements followed each other in the order of arithmetic succession of the size
of their atoms:
Li = 7;
Na = 23;
K = 39;
Be = 9.4;
Mg = 24;
Ca = 40;
B = 11;
Al = 27.4;
......
C = 12;
Si = 28;
Ti = 50;
N= 14;
P= 31;
V = 51
O = 16;
S = 32;
F = 19;
Cl = 35.3
In the arrangement of elements with atoms greater than 100, we meet an entirely analogous
continuous order:
Ag = 108; Cd = 112; Ur 116; Sn = 118; Sb = 122; Te = 128;
I = 127.
It has been shown that Li, Na, K, and Ag are related to each other, as are C, Si, Ti, Sn, or as are
N, P, V, Sb, etc. This at once raises the question whether the properties of the elements are
expressed by their atomic weights and whether a system can be based on them. An attempt at
such a system follows.
In the assumed system, the atomic weight of the element, unique to it, serves as a basis for
determining the place of the element. Comparison of the groups of simple bodies known up to
now according to the weights of their atoms leads to the conclusion that the distribution of the
elements according to their atomic weights does not disturb the natural similarities which exist
between the elements but, on the contrary, shows them directly. .
All the comparisons which I have made in this direction lead me to conclude that the size of the
atomic weight determines the nature of the elements, just as the weight of the molecules
determines the properties and many of the reactions of complex bodies. If this conclusion is
confirmed by further applications of this approach to the study of the elements, then we are near
an epoch in understanding the existing differences and the reasons for the similarity of
elementary bodies.
I think that the law established by me does not run counter to the general direction of natural
science, and that until now it has not been demonstrated, although already there have been hints
of it. Henceforth, it seems to me, there will be a new interest in determining atomic weights, in
discovering new elementary bodies, and in finding new analogies between them.
I now present one of many possible systems of elements based on their atomic weights. It serves
only as an attempt to express those results which can be obtained in this way. I myself see that
this attempt is not final, but it seems to me that it clearly expresses the applicability of my
assumptions to all combinations of elements whose atoms are known with certainty. In this I
have also wished to establish a general system of the elements. Here is this attempt:
Ni =
H=1
Li = 7
Be = 9.4
B = 11
C = 12
N = 14
O = 16
F = 19
Na = 23
Mg = 24
Al = 27.4
Si = 28
P = 31
S = 32
Cl = 35.5
K = 39
Ca = 40
? = 45
?Er = 56
?Yt = 60
?In = 75.6
Ti = 50
V = 51
Cr = 52
Mn = 55
Fe = 56
Co = 59
Cu = 63.4
Zn = 65.2
? = 68
? = 70
As = 75
Se = 79.4
Br = 80
Rb = 85.4
Sr = 87.6
Ce = 92
La = 94
Di = 95
Th = 118?
Zr = 90
Nb = 94
Mo = 96
Rh = 104.4
Ru = 104.4
Pd = 106.6
Ag = 108
Cd = 112
Ur = 116
Sn = 118
Sb = 122
Te = 128?
J = 127
Cs = 133
Ba = 137
? = 180
Ta = 182
W = 186
Pt = 197.4
Ir = 198
Os = 199
Hg = 200
Au = 197?
Bi = 210?
Tl = 204
Pb = 207
Mendeleev, D. The Relationship Between the Properties and Atomic Weights of the Elements. Journal of
the Russian Chemical Society, 1: 60-77 (1869).