2 THE PERIODICTABLE
successive eighth element was^4 a kind of repetition of the first'. A few
years later, Lothar Meyer and Mendeleef, independently, suggested
that the properties of elements are periodic functions of their atomic
weights. Lothar Meyer based his suggestion on the physical properties
of the elements. He plotted 'atomic volume'—the volume (cm^3 ) of the(^70) r
60
50
QJ
§ 40
o
< 30
20
10 Ll
20 40 60 80
Atomic weight
100 120
_j
140
Figure Ll. Atomic volume curve (Lothar Meyer]
atomic weight (g) of the solid element- against atomic weight. He
obtained the graph shown in Figure LL We shall see later that many
other physical and chemical properties show periodicity (p. 15).
'VALENCY' AND CHEMICAL PROPERTIES
Mendeleef drew up a table of elements considering the chemical
properties, notably the valencies, of the elements as exhibited in their
oxides and hydrides. A part of Mendeleef s table is shown in Figure
1.2 -note that he divided the elements into vertical columns called
groups and into horizontal rows called periods or series. Most of
the groups were further divided into sub-groups, for example Groups