Chapter 24. -NUCLEAR POWER PLANTS 



CLECmON (•) 



HYDROOEN 



A 



OXYCEN 



41.2 

 Figure 24-1.— Rutherford-Bohr models 

 of simple atoms. 



Two elementary particles, protons and neu- 

 trons, often referred to as nucleons, compose the 

 atomic nucleus. The positive charge of atomic 

 nuclei is attributed to the protons. A proton has 

 an electrical charge equal and opposite to that of 

 an electron. A neutron has no charge. 



The number of electrons in an atom and 

 their relative orbital positions predict how an 

 element will react chemically, whereas the 

 number of protons in an atom determines which 

 element it is. An atom which is not ionized 

 contains an equal number of protons and elec- 

 trons; thus it is said to be neutral, since the 

 total atomic charge is zero. 



As shown in part A of figure 24-1, the 

 hydrogen atom has a single proton in the nucleus 

 and a single orbital electron. Hydrogen, the 

 lightest element, is said to have a mass of 

 approximately one. The next heavier atom, 

 that of helium (part B of fig. 24-1), had a mass 

 of four relative to hydrogen and was expected 

 to contain four protons. It was found that the 

 helium atom has only two protons instead of the 

 four expected; the remainder of its mass is 

 attributed to two neutrons located in the nucleus 

 of the helium atom. The more complex atoms 

 contain more protons and neutrons in the 



Figure 24-2.— Characteristics of 

 atomic particles. 



147.154 

 elementary 



nucleus, with a corresponding increase in the 

 number of planetary electrons. The planetary 

 electrons are arranged in orbits or shells of 

 definite energy levels outside the nucleus. 



The characteristics of the elementary atomic 

 particles are compiled in figure 24-2, Note 

 that the mass of a proton is much greater than 

 that of an electron; it takes about 1847 electrons 

 to weigh as much as one hydrogen proton. 



It is possible for atoms of the same element 

 to have different numbers of neutrons, and 

 therefore different masses. Atoms which have 

 the same atomic number (number of protons in 

 the atom) but different masses are called 

 isotopes . Different isotopes of the same element 

 are identified by the atomic mass number, 

 which is the total number of neutrons and 

 protons contained within the nucleus of the 

 atom. 



The element hydrogen has three known 

 isotopes, as shown in figure 24-3. The simplest 

 and most common known form of hydrogen 

 consists of 1 proton, which is the nucleus, 

 and 1 orbital electron. Another form of hydro- 

 gen, deuterium, consists of 1 proton and 1 

 neutron forming the nucleus. The third 

 form, tritium, consists of 1 proton and 2 

 neutrons forming the nucleus and 1 orbital 

 electron. 



In scientific notation, the three isotopes 

 of hydrogen are written as follows: 



H^ 



Common hydrogen 



.1 



Deuterium 



H 



Tritium 



.1 



H 



In this notation, the subscript preceding 

 the symbol of the element indicates the atomic 

 number of the element. The superscript following 



615 



