The Structure of Matter

Author: E.E. Kimberly

All matter is believed to be made up of atoms. Nothing was known about the structure of atoms until Thomson discovered in 1895 that they contain both positively and negatively charged electrical particles. The positively charged particle is called a proton and has a mass of approximately 1 atomic-weight unit. The negatively charged particle is called an electron and has a mass about 1/1840 times that of a proton. The hydrogen atom consists of one proton and one electron. The electron rotates in an orbit about the proton as if in a miniature solar system. The negative charge on the electron has the same magnitude as the positive charge on the proton, and so a combination of the two exhibits no electrical manifestations.

An atom may contain more than one proton and usually contains as many electrons as protons. The proton group, regardless of the number of protons it contains, is called the nucleus of the atom. Chemical elements are different one from the other because of the different numbers of protons and electrons contained in their atoms. The characteristics of atoms are not entirely accounted for by assuming only protons and electrons in their structures. As more is learned about the atom, additional particles - such as neutrons, positrons, and mesons - are imagined in order to explain the new characteristics that are discovered. In the present state of the science of engineering, only protons and (electrons are useful in explaining electrical phenomena.