Georgia Institute Of Technology

• PHYS 2213

• CHAPTER 4 Structure of the Atom In the present first part of the paper the mechanism of the binding of electrons by a positive nucleus is discussed in relation to Planck’s theory. It will be shown that it is possible from the point of view taken to account in a simple way for the law of the line spectrum of hydrogen. - Niels Bohr, 1913 Structure of the Atom Pieces of evidence that scientists had in 1900 to indicate that the atom was not a fundamental unit: 1) There seemed to be too many kinds of atoms, each belonging to a distinct chemical element. 2) Atoms and electromagnetic phenomena were intimately related. 3) The problem of valence. Certain elements combine with some elements but not with others, a characteristic that hinted at an internal atomic structure. 4) The discoveries of radioactivity, of x rays, and of the electron.  Thomson’s “plum-pudding” model of the atom had the positive charges spread uniformly throughout a sphere the size of the atom, with electrons embedded in the uniform background.  In Thomson’s view, when the atom was heated, the electrons could vibrate about their equilibrium positions, thus producing electromagnetic radiation. Thomson’s