The Paull Exclusion Principle
In Chapter 40 we considered a variety of electron traps. from fictional one-dimension altars to the real three-dimensional trap of a hydrogen atom. In all those examples.we trapped only one electron, However. when we discuss traps containing two or more electrons (as we shall in the next two sections). we must consider a principle that governs any panicle whose spin quantum numbers is not zero or an integer. This principle applies not only to electrons but also to protons and neutrons. all of which have s = }. The principle is known as the Pauli exclusion principle after Wolfgang Pauli. who formulated it in 1925. For electrons. it states that
*No two electrons confined to the same trap can have the same set of values for its quantum numbers
As we shall discuss in Section 41-9. this principle means that no two electrons in an atom can have the same four values for the quantum numbers Ii. I. m., and m., In other words. the quantum numbers of any two electrons in an atom must
differ in at least one quantum number. Were this not true. atoms would collapse. and thus you and the world as you know it could not exist.