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characters”.
30
According to Mendeleev, this “can be clearly seen in the row Li,
Be, B, C, N, O, F”
31
:
Li
¼
7 e
¼
9.4
B
¼
11
C
¼
12
N
¼
14
O
¼
16
F
¼
19
Valency
1
2
3
4
3
2
1
Thus, “Li and F are monovalent and are most widely separated with respect to
electrochemical behaviour; Be and O, which succeed them, are divalent; then come
trivalent B and N and, in the centre, tetravalent carbon has its place.”
32
This
phenomenon appeared moreover to be “repeated in other rows”.
33
“If we consider
the distance between Na and Cl, Ag and I, and others,” Mendeleev remarked, “we
also notice that the arrangement of elements according to the magnitude (of their
atomic weights) corresponds in a certain degree to the valency and to the concept
of affinity.”
34
Due to the recurring nature of this phenomenon, Mendeleev con-
cluded that, “when arranged according to their atomic weights, the elements display
a distinct periodicity in their properties”.
35
Mendeleev
s personal viewpoints on the
periodic law
were even more clearly stated in the first edition of his
Osnovy khimii
:
The regular and gradual
changes in the size of atomic weights involves
[
'
]
the regular and
gradual changes
in the qualitative as well as in the quantitative
capability of elements for
compounds
. In addition, there is a
periodic repetition
of both qualitative and quantitative
characteristics, consonant with the gradual increase in atomic weight. This is the conclusion
of all comparisons made in this regard and this opens, in my view, a new perspective on the
elements.
36
...
Mendeleev
s insight in the subject matter, as well as the vital importance of the
periodic law
in classifying the chemical elements, cannot be overestimated. Never-
theless, and quite unfortunately, it could not be accredited a universal character, as it
did not apply to the whole of chemical elements. After all, in the case of primary
groups, there were of course “regular and gradual changes in the size of atomic
weights”,
37
but
these were
not
accompanied by “the regular and gradual changes”
38
in the distinctive properties of the elements. In the case of the cerium group, for
example:
'
Ce
¼
92
La
¼
94
Di
¼
95
Valency
2
2
2
30
Mendeleev (1869b/t), op. cit., p. 33. (see note 16)
31
Loc. cit.
32
Ibid., p. 27.
33
Ibid., p. 33.
34
Ibid., p. 27.
35
Ibid., p. 33.
36
Mendeleev, D. I.
Osnovy Khimii
. 2 vols. 1st ed. St. Petersburg: Obshchestvennaia pol za, 1868-
1871. English translation by Trifonov, D. N. “Views of D. I. Mendeleev on Rare Earths.” In
Rare
-
Earth Elements and Their Position in the Periodic System
. New Delhi: Indian National Scientific
Documentation Centre, 1970. Emphasis in original.
37
Loc. cit.
38
Loc. cit.
