Atomic Physics Delta College：原子物理学 三角洲大学.ppt

Atomic Physics Chapter 28 Atomic Models Introduction How do neon signs work? Our main focus will be on the hydrogen atom. It is the simplestatomic system. Why is it important to study the hydrogen atom? Studying the quantum numbers for the allowed states of hydrogen will help us to describe the allowed states of more complex atoms. The hydrogen atom is an ideal system for relating theory to experimentation. Much that we learn about hydrogen can be extended to single electron ions like He and Li. Early Models Of The Atom The Greek model Tiny, hard, indestructible sphere 3 The J. J. Thomson model A volume of positive charge is embedded with negative charges called “electrons” The Rutherford model A positive nucleus orbited by electrons. The nucleus contains 99.9% of the atom’s mass The Rutherford model Which force holds the electrons in orbit? The Coulomb force Problems with the Rutherford Model There were two basic difficulties with the Rutherford model. It could not explain why atoms radiate discrete frequencies. Accelerating electrons should radiate electromagnetic waves. Electron Transitions Using a high voltage to move electrons through a gas causes the gas electrons to become excited and to jump from lower energy levels to higher energy levels. Photons of various wavelengths are produced when electrons fall from higher energy levels to lower energy levels. Emission Spectra The emission spectrum of hydrogen Can be produced by applying a high voltage across an evacuated glass tube filled with hydrogen The observed wavelengths are characteristic only of hydrogen 279, 57 The Balmer Series In the Balmer Series nf = 2 There are four prominent wavelengths 656.3 nm (red) 486.1 nm (green) 434.1 nm (purple) 410.2 nm (deep violet) 278, 28.7 Balmer Wavelengths The Balmer Series Wavelength Equation RH is the Rydberg constant RH = 1.0973732 x 107 m-1 Two Other Important Series Lyman series (UV) nf = 1 Paschen series (IR) nf = 3 70 Spectral Line