Chemistry Reference
In-Depth Information
Fig. 11.5 Dmitrii
Ivanovich Mendeleev
in the year 1870
11.2.2 Atomic Weight Corrections and Valency Shifts
In that same year 1870, Mendeleev (Fig.
11.5
) also wrote an article
On the
Placement of Cerium in the Periodic System of Elements
, where he admitted that
“the atomic weights of indium, uranium and cerium (and probably its associates)
should be modified because these elements do not fit in on the basis of either the
form of their oxides or their properties according to the periodicity indicated by
me.”
63
He realised that a change in valency would be necessary in order to correct
the atomic weight values of the rare earths. The usual representation of their oxides
by the formula RO had thus to be modified. Mendeleev was the first in assuming the
rare earths to be trivalent, instead of bivalent, and he therefore proposed the general
formula R
2
O
3
for the rare-earth oxides. In the case of cerium, which represented
two degrees of oxidation, Mendeleev proposed “that the ordinary degree of oxida-
tion [
] be allotted the formula Ce
2
O
3
”, while “the higher oxide will have the
simple composition CeO
2
.”
64
Similar statements appeared in his article
Concerning
the Natural System of
...
the Elements and Its Application in Determining the
63
Mendeleev, D. I. “On the Placement of Cerium in the Periodic System of Elements.”
Bulletin de
l
Academie imperiale des sciences de St
.-
P ´tersbourg
16 (1870/1871): 45. English translation by
Trifonov (1970), op. cit., p. 40. (note 36) This paper was completed in November 24, 1870.
Originally, Mendeleev had written one big article on “the system of the elements” but this was
afterwards subdivided in Mendeleev (1870/1871) and Mendeleev (1871a). (note 65)
64
Loc. cit. English translation by Trifonov (1966), op. cit., p. 25. (note 29)
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