Principles of naval engineering - Historic Naval Ships Association

Chapter 24. -NUCLEAR POWER PLANTSCLECmON (•)ParticleHYDROOENAOXYCEN41.2Figure 24-1.— Rutherford-Bohr modelsof simple atoms.Two elementary particles, protons and neutrons,often referred to as nucleons, compose theatomic nucleus. The positive charge of atomicnuclei is attributed to the protons. A proton hasan electrical charge equal and opposite to that ofan electron. A neutron has no charge.The number of electrons in an atom andtheir relative orbital positions predict how anelement will react chemically, whereas thenumber of protons in an atom determines whichelement it is. An atom which is not ionizedcontains an equal number of protons and electrons;thus it is said to be neutral, since thetotal atomic charge is zero.As shown in part A of figure 24-1, thehydrogen atom has a single proton in the nucleusand a single orbital electron. Hydrogen, thelightest element, is said to have a mass ofapproximately one. The next heavier atom,that of helium (part B of fig. 24-1), had a massof four relative to hydrogen and was expectedto contain four protons. It was found that thehelium atom has only two protons instead of thefour expected; the remainder of its mass isattributed to two neutrons located in the nucleusof the helium atom. The more complex atomscontain more protons and neutrons in the