IV.

Interactions

Elementary particles exert forces on each other, and they are constantly created and annihilated. Forces and processes of creation and annihilation, are, in fact, related phenomena and are collectively called interactions. Four types of interaction, or fundamental forces, are known:

Nuclear, or strong, interactions are the strongest and are responsible for the binding of protons and neutrons to form nuclei. Next in strength are the electromagnetic interactions that are responsible for binding electrons to nuclei in atoms and molecules. From the practical viewpoint, this binding is of great importance because all chemical reactions represent transformations of such electromagnetic binding of electrons to nuclei. Much weaker are the so-called weak interactions that govern the radioactive decay of atomic nuclei, first observed (1896-1898) by the French physicists and chemists Antoine H. Becquerel, Pierre Curie, and Marie Curie. The gravitational interaction is important on a large scale, although it is the weakest of the elementary particle interactions.