The questions raised by this fund of knowledge remained unanswered until the internal structure of atoms began to be unraveled at the end of the 19th century. The classic view, proposed by John Dalton, that atoms are irreducible, unchangeable entities, virtually eliminated the prospect of understanding their properties, for it implied the absence of internal structure. The mutability of atoms, and hence the first glimmerings of an understanding of their constitution and their properties, came with the discovery of the electron as a universal constituent of matter. The electron was the first subatomic particle to be discovered and in due ...(100 of 27318 words)