Atom, Bohr theory simple model

As we learned in Chapter 1, science gives insight into nature through models or theories that explain laws and predict behavior. Here we look at the Bohr model, a theoiy for the way electrons behave in atoms that explains the periodic law and links the macroscopic properties of elements to the microscopic properties of their atoms. We must keep in mind that this is a model for the atom and not the real thing. In fact, a more successful and complete model for the atom, called the quantum mechanical model, is significantly different, as we shall see in the next section. Nonetheless, the simple model developed here helps us to understand the periodic law and allows us to predict a great deal of chemical behavior. 

Chemists were quick to appreciate Bohr s model because it provided an extremely clear and simple interpretation of chemistry. It explained the reason behind Mendeleev s table, that the position of each element in the table is nothing other than the number of electrons in the atom of the element, which, of course, represents an equal number of periodic changes in the nucleus. Each subsequent atom has one more electron, and the periodic valence changes reflect the successive filling of the orbital. Bohr s model also provided a simple basis for the electronic theory of valence. 

In recent years the old quantum theory, associated principally with the names of Bohr and Sommerfeld, encountered a large number of difficulties, all of which vanished before the new quantum mechanics of Heisenberg. Because of its abstruse and difficultly interpretable mathematical foundation, Heisenberg s quantum mechanics cannot be easily applied to the relatively complicated problems of the structures and properties of many-electron atoms and of molecules in particular is this true for chemical problems, which usually do not permit simple dynamical formulation in terms of nuclei and electrons, but instead require to be treated with the aid of atomic and molecular models. Accordingly, it is especially gratifying that Schrodinger s interpretation of his wave mechanics3 provides a simple and satisfactory atomic model, more closely related to the chemist s atom than to that of the old quantum theory. 

The Bohr model (1913) of atomic structure is a simple quantum mechanical model electrons can only have certain values or quantities of energy. The Bohr model was also quantitative and accounted for Balmer s formula. However, Bohr s original theory was flawed and could not account for the spectra of atoms other than the hydrogen atom (or related species, for example He ) and has been replaced by Schrodinger s quantum mechanical model. Anyone who is not shocked by quantum theory has not understood it , is a saying attributed to Bohr. 

---