Atoms, Ions, Electrons, Atomic Nuclei, Photons

Abstract

We begin our discussion of the structure of matter by demonstrating the evidence for the existence of individual atoms and their constituent parts: electrons, ions, and nuclei. For it is the properties and behavior of these particles with which atomic physics deals and from which atomic physicists hope to derive all other properties of matter. When we speak of the atom as being the smallest particle of matter — when we say, for instance, that the iron atom is the smallest particle into which a piece of iron can be divided — we mean that the parts of an iron atom do not show any more the chemical characteristics typical for that element. We make this distinction because it has been known for a long time now that the atom can be broken down into smaller particles. It was in the present century that the existence of atoms as the smallest units in the meaning mentioned above was conclusively proved by experiments. These will be presented in this book. As recently as in the latter part of the last century a vehement scientific debate was waged over the question whether the atom existed as an actual physical entity, or whether the atomic hypothesis was merely a convenient working hypothesis for explaining many observations which had been made on the behavior of matter. In the following pages we shall discuss the evidence for the atomic structure of matter and, at the same time, the proof for the atomicity of the electric charge and thus of electricity itself since it is now known that matter and electricity are inseparably related.