The Periodic Laws

The periodic law of the elements is the most fundamental principle of chemistry. It became firmly established in about 1875 amidst one of the most bitter controversies since the collapse of the phlogiston theory. The principle at issue is best remembered as Prout's hypothesis. To account for the fact that most of the atomic weights, that provided the basis for periodic classification, were measured to be uniformly close to whole numbers, it postulated hydrogen as the basic building block of all matter. Of the common elements some typical (modern) relative atomic weights that illustrate the point, include H(1.008), He(4.003), Be(9.012), C(12.011), N(14.007), O(15.999), F(18.998), Na(22.990), and many more. The most conspicuous exceptions to the rule, the elements Cl(35.453), Cu(63.546) and Rb(85.468) became the subject of intense research aimed at the refutation of Prout's hypothesis, by the measurement of the most accurate atomic weights. The results refuted the hypothesis which eventually however, prevailed with the discovery of isotopes.