THE PERIODIC LAW
The work which had been done upon the atomic weights rendered possible one of the most brilliant generalizations of modern times, in this field. This was thePeriodic Law. In the year 1864, Newlands published a Table containing the various elements arranged in the order of their atomic weights. In a side column the differences between these weights were given, each being deducted from the one next higher in the scale. The next year, Newlands announced his “law of octaves,” whichhe deduced from his arrangement of the elements. He said in part that: “If the elements are arranged in the order of their equivalents, with a few slight transpositions ... it will be observed that elements, belonging to the same group usually appear on the same horizontal line.... It will also be seen that the number of analogous elements generally differ either by seven or by some multiple of seven; in other words, members of the same group stand to each other in the same relation as the extremities of one or more octaves in music.”
This pioneer work of Newlands rendered possible the Periodic Law, as finally formulated and worked out in detail by Mendeleeff. Briefly, the Law states that “the properties of an element are a periodic function of its atomic weight.”
This is merely another way of saying that if you know the atomic weight of an element, you also know its properties, since these are fixed or invariable. Mendeleeff arranged the elements in various “Groups,” according to their atomic weights, and it was found that the properties of the elements periodically recur as the weights of the atoms rise. There were certain empty spaces in Mendeleeff’s Table, waiting for new elements which should fit into these empty spaces, if discovered. At the time they had not been discovered; but several of them have been since, and it is a remarkable fact that they invariably fit into his table exhibiting all the properties whichthey should theoretically exhibit, and might have been predicted to, years before. This is one of the surest confirmations of the accuracy of Mendeleeff’s general Law, and is one of the finest generalizations ever made in science.
The conclusion which we may draw from this Law is that there is a definiterelationshipbetween the chemical elements. How or why this relationship existed was not known at the time, and only became clear half a century later, when the newer discoveries concerning the ultimate constitution of matter rendered this clear.