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
Periodic Table according to D I Mendeleev, 1869
? = 180
Ta = 182
W = 186
Pt = 197.4
Ir = 198
Os = 199
Hg = 200
Au = 197?
Bi = 210?
Tl = 204
Pb = 207
…… In conclusion, I consider it advisable to recapitulate the results of the above work.
1. Elements arranged according to the size of their atomic weights show clear periodic properties.
2. Elements which are similar in chemical function either have atomic weights which lie close together (like Pt,
Ir, Os) or show a uniform increase in atomic weight (like K, Rb, Cs). The uniformity of such an increase in the
different groups is taken from previous work. In such comparisons, however, the workers did not make use of
the conclusions of Gerhardt, Regnault, Cannizzaro, and others who established the true value of the atomic
weights of the elements.
3. Comparisons of the elements or their groups in terms of size of their atomic weights establish their so-called
"atomicity" and, to some extent, differences in chemical character, a fact which is clearly evident in the group
Li, Be, B, C, N, 0, F, and is repeated in the other groups.
4. The simple bodies which are most widely distributed in nature have small atomic weights, and all the
elements which have small atomic weights are characterized by the specificity of their properties. They are
therefore the typical elements. Hydrogen, as the lightest element, is in justice chosen as typical of itself.
5. The size of the atomic weight determines the character of the element, just as the size of the molecule
determines the properties of the complex body, and so, when we study compounds, we should consider not only
the properties and amounts of the elements, not only the reactions, but also the weight of the atoms. Thus, for
example, compounds of S and Te, Cl and I, etc., although showing resemblances, also very clearly show
differences.
6. We should still expect to discover many unknown simple bodies; for example, those similar to Al and Si,
elements with atomic weights of 65 to 75.
7. Some analogies of the elements are discovered from the size of the weights of their atoms. Thus uranium is
shown to be analogous to boron and aluminium, a fact which is also justified when their compounds are
compared.
The purpose of my paper will be entirely attained if I succeed in turning the attention of investigators to the
same relationships in the size of the atomic weights of non-similar elements, which have, as far as I know, been
almost entirely neglected until now. Assuming that in problems of this nature lies the solution of one of the
most important questions of our science, I myself, as my time will permit, will turn to a comparative study of
lithium, beryllium, and boron.
Mendeleev, D. The Relationship Between the Properties and Atomic Weights of the Elements. Journal of the Russian
Chemical Society, 1: 60-77 (1869).