460 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



system, in which only 7 families were recognised, and his 

 own, in which there were 19. 



Nearly all the elements were classified, according to the 

 general scheme of Newlands's octaves, in seven GROUPS, 

 numbered I to VII, arranged in seven vertical columns 

 under the seven TYPICAL ELEMENTS 1 (loc. cit. p. 152) : 



Li Be B C N O F 



When the elements, in the order of their atomic weights, 

 had been allotted to their proper families they formed not 

 fewer than thirteen horizontal SERIES or SHORT PERIODS (loc. 

 tit. p. 145), of which the first was occupied by hydrogen 

 only, and the second by the seven typical elements referred 

 to above. 



Mendeleeff, like Newlands, now found that the chief 

 triads appeared in alternate short periods or octaves, and 

 therefore distinguished between the EVEN SERIES and the 



ODD SERIES (IOC. tit. p. 145), e.g. 



This difficulty was overcome (again following Lothar Meyer) 

 by placing the members of the even series on the left hand, 

 and the members of the odd series on the right hand side 

 of the vertical columns ; in this way the number of columns 

 was virtually increased to fourteen and each group could be 



centre of the columns instead of left and right ; (3) The four series 

 8, 9, 10, II have been compressed into two lines by clustering 15 rare 

 earth elements into a single space in the table ; (4) The elements Sc, 

 Ga, Ge, predicted by Mendeleeff have been inserted, and other missing 

 elements are indicated by numbers of a consecutive series (see below, 

 p. 491). 



1 The phrase was derived from Gerhardt's "simple inorganic types' 3 

 (p. 425), the chief of which may be recognised in the series 



CH 4 NH 3 OH 2 FH (compare C1H). 



