Chemistry Reference
In-Depth Information
11.1.7
Table Layouts
First of all, Mendeleev naturally wondered how one should depict both primary and
secondary groups within his
Attempted System
. “Perhaps as a consequence of the
closer study of these [primary] groups,” said Mendeleev, “the system of elements
arranged in [primary and secondary] groups will have to be changed such that in
certain parts of the system the similarity between members of the horizontal rows
will have to be considered [i.e. secondary group], but in other parts, the similarity
between members of the vertical columns [i.e. primary group].”
25
Notice that, in
comparison with Mendeleev
s
first attempt
, all rows and columns have been
interchanged in the
Attempted System
. Thus what used to be a vertical group of
elements in the
first attempt
(e.g. Li, Na, K,
'
...
) has been transformed into a
horizontal group in the
Attempted System
. As a result, all secondary groups are
now lying horizontally. The primary groups, on the other hand, are laid out
vertically in Mendeleev
s
Attempted System
. Of course, whether a secondary
group is lying horizontally (as in the
Attempted System
) or vertically (as in the
first attempt
) does not really matter. Of greater importance is the simultaneous
existence of both primary
and
secondary groups in
one
classificatory system of the
elements, and the way this is represented in the table layout.
'
11.1.8 Transitional Function of Primary Groups
A more significant consequence of the existence of primary groups within the
periodic system is their so-called
transitional function
. Mendeleev hit upon this
substantial idea when he was examining the
Attempted System
.Itappearedtohim
that the elements of the primary groups at the upper part of his system represented
some sort of transition between two (sub)periods in the periodic table. “It must be
remarked,” he said, “that the upper members of the fourth column (Mn, Fe, Co, Ni,
Zn) form a
transition
to the lower members of the (third) column in which Ca, K, Cl
and similar elements are found. Thus the properties and atomic weights of cobalt and
nickel, chromium, manganese, and iron represent a
transition from copper and zinc to
calcium and potassium
.”
26
In all probability, this quotation lies at the origin of the
term
transition metals
—a very powerful and important concept for the further
development of the periodic table (see further). Nonetheless, at the beginning of
1869, Mendeleev
s views on the matter were still rather intuitive and somewhat
vague. Indeed, it was not easy to perceive the transitional function of the iron group,
the palladium group, and the platinum group in the
Attempted System
.
27
'
25
Loc. cit.
26
Ibid., p. 30. Emphasis added.
27
The transitional function of these primary groups must have manifested itself much more
sharply during the construction process of the
first attempt
.
