Physical Chemistry for Beginners

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899. Excerpt: ... CHAPTER VII. THE PERIODIC SYSTEM. § 69. Definition. The periodic system is a grouping of the elements which depends upon the law that the properties of the elements, so far as these may be expressed by numbers, are periodic functions of their atomic weights. Remark 1. The quantity A is a function of the quantity B, if they alter simultaneously, and if to every value of B there corresponds one or more values of A. Thus A is a function of B in the following equations: A = 3B; A = B"; A=/(B"+A; A = arc sin B. A is aperiodic function of B if on a continuous increase in the value of B the value of A is the same at regular intervals. Thus in the equation A = sin B A is a periodic function of B, since for every value of B A has a certain value; A will, however, have the same value if B is 360 or 720 or n times 360 greater, and accordingly for every interval of 360 A again receives the same value. This interval is called a period, and the series of values 146 which A receives while B is passing through an interval is also called a period. Remark 2. The basis of the periodic system is the periodic function. Nevertheless the periodicity is not associated with mathematical exactitude with a period of definite interval. The theory may therefore be brought into closer agreement with the facts if it be stated that when the elements are arranged in the order of their increasing atomic weights they may be separated into definite groups, and the properties of any one group can be found recurring in the others at certain stated positions. Remark 3. A relation between the properties of the elements and their atomic weights has long been sought, it having been observed that a mathematical relation exists between the atomic weights of those elements which, from their gen...