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Nuclear Chemistry
All the chemical changes and many of the physical changes that we have
studied so far involve alterations in the electronic structures of atoms.
Electron-transfer reactions, emission and absorption spectra, and X rays result
from the movement of electrons from one energy level to another. In all of
these, the nuclei of the atoms remain unchanged, and different isotopes of the
same element have the same chemical activity. Nuclear chemistry, or radioactivity, differs from other branches of chemistry in that the important changes
occur in the nucleus. These nuclear changes also are represented by chemical
equations. However, because the isotopes of the same element may, from a
nuclear standpoint, be very different in reactivity, it is necessary that the equations show which isotopes are involved.
NUCLEAR EQUATIONS
Nuclear symbolism disregards valence and electrons and always includes the
mass number of the isotope (the whole number nearest the atomic weight of the
isotope), the atomic number of the element, and the symbol of the element. The
mass number is shown as a superscript preceding the symbol, and the atomic
number is shown as a subscript preceding the symbol. This notation is illustrated by the following examples: