Page:Popular Science Monthly Volume 59.djvu/173

Rh

Most tables present a difficulty in that they place sodium in the group or sub-group with copper, silver and gold, while it would most naturally fall in the group with lithium, potassium, rubidium and cesium. So magnesium would be placed according to its properties, not so closely with zinc and cadmium, as with glucinum, calcium, strontium and barium. Fluorin belongs rather with chlorin, bromin and iodin than with manganese, the metal with which it is associated in most tables. So oxygen belongs with sulfur, selenium and tellurium, rather than with chromium and molybdenum. This is remedied in Venable's table. The first element in any group the author calls the group element or bridge element; for it often possesses properties which ally it to the elements of the next groups. The second element he calls the type element, and in this is, as it were, shadowed forth the character of the succeeding elements of the same group. From this point on, the group is divided into two series, one more and the other less electro-positive or negative, as the case may be. The first three groups are for the most part made up of electro-positive elements, while those of the fifth, sixth and seventh groups are relatively electronegative. Now in the former the elements of the more positive series resemble the type element of their group more strongly than those of the less positive series. In the relatively negative fifth, sixth and seventh groups, the reverse is the case. This grouping thus places sodium with potassium and chlorin with bromin. In the fourth group,