What observations led to the periodic law? what observations led to the periodic law? observation that certain elements possess such property as radioactivity observation that the all halogen elements have similar properties observation that the all metals have similar properties observation that the properties of elements recur and certain elements have similar properties?

HISTORICAL INTRODUCTION.1 EVER since the establishment of the atomic theory by Dalton and Berzelius it was felt among chemists that there must be some relation between the atomic weights of the different elements and their properties. It was recognized very early that there exist groups of elements possessing related chemical and physical properties, and one of the earliest attempts to bring out this point is due to Dobereiner. In 1829 he tried to show that “many elements may be arranged in groups ()f three, in each of which the middle element has an atomic weight equal or approximately equal to the mean of the atomic weights of the two extremes.” As illustrations of this method of arrangement may be mentioned the following groups: Li, Na, K; Ca,Sr,