Ideas of Quantum Chemistry P7 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 26 1. The Magic of Quantum Mechanics Enrico Fermi 1901-1954 Italian physicist professor at universities in Florence Rome New York and in 1941-1946 at the University of Chicago. Fermi introduced the notion of statistics for the particles with a half-integer spin number called fermions during the Florence period. Dirac made the same discovery independently hence this property is called the Fermi-Dirac statistics. Young Fermi was notorious for being able to derive a formula from any domain of physics faster than someone sent to find it in textbooks. His main topic was nuclear physics. He played an important role in the A bomb construction in Los Alamos and in 1942 he built the world s first nuclear reactor on a tennis court at the University of Chicago. Fermi was awarded the Nobel Prize in 1938 for his demonstration of the existence of new radioactive elements and for results obtained with them especially with regard to artificial radioactive elements . The spin quantum number s characteristic of the type of particle31 often called simply its spin can be written as s n where n may be zero or a natural number an integer or half-integer number . The particles with a half-integer s . s fermions 2 for electron proton neutron neutrino are called fermions the particles with an integer s . s 1 for deuteron photon 37 38 s 0 for meson n and meson K bosons are called bosons. The magnetic39 spin quantum number ms quantizes the z component of the spin angular momentum. Thus a particle with spin quantum number s has an additional spin degree of freedom or an additional coordinate - spin coordinate a. The spin coordinate differs widely from a spatial coordinate because it takes only 2s 1 discrete values Fig. associated to s s 1 . 0 . s. Most often one will have to deal with electrons. For electrons the spin coordinate a takes two values often called up and down . We will arbitrarily choose a 2 and a 2 Fig. b. Satyendra Nath Bose 1894 1974 Indian physicist .
