Abstract The origins of atomic physics were entwined with the development of quantum mechanics itself ever since the first model of the hydrogen atom by Bohr. This introductory chapter surveys some of the early ideas, including Einstein’s treatment of the interaction of atoms with radiation, and a classical treatment of the Zeeman effect. These methods, developed before the advent of the Schrodinger equation, remain useful as an intuitive way of thinking about atomic structure and transitions between the energy levels. The ‘proper’ description in terms of atomic wave functions is presented in subsequent chapters.
Abstract The origins of atomic physics were entwined with the development of quantum mechanics itself ever since the first model of the hydrogen atom by Bohr. This introductory chapter surveys some of the early ideas, including Einstein’s treatment of the interaction of atoms with radiation, and a classical treatment of the Zeeman effect. These methods, developed before the advent of the Schrodinger equation, remain useful as an intuitive way of thinking about atomic structure and transitions between the energy levels. The ‘proper’ description in terms of atomic wave functions is presented in subsequent chapters.
The first objective of this chapter is to briefly review some of the basic ideas about the structure of matter, in particular the concepts of microscopic physics, in order to recall the knowledge gained in previous physics (and chemistry) courses and make it more precise. Our review will be very concise, and most statements will be made without any proof or detailed discussion. A second objective is to give a brief description of some of the crucial stages in the early development of quantum physics. We shall not follow the strict historical order of this development or present the arguments used at the beginning of the last century by the founding fathers of quantum mechanics; rather, we shall stress the concepts which we shall find useful later on. Our last objective is to give an elementary introduction to some of the basic ideas, like those of a quantum particle or energy level, that will reappear throughout this text. We shall base our review on the Bohr theory, which provides a simple, though far from convincing, explanation of how energy levels are quantized and how the spectrum of the hydrogen atom arises. This chapter should be reread later on, once the basic ideas of quantum mechanics have been made explicit and illustrated by examples. From the practical point of view, it is possible to skip the general considerations of Sections 1.1 and 1.2 at the first reading and begin with Section 1.3, returning to those two sections later on as needed.
Quantum mechanics began in very early twentieth century when Max Planck found the expression for black body thermal radiation in which the emitted light was not a continuum as postulated by classical physics. Erwin Schrodinger applied his equation to solve the quantum harmonic oscillator, the quantum rigid rotor, and a hydrogen-like atom. Pertaining to the solution of the Schrodinger equation to hydrogen atoms are the quantum numbers. C. K. Ingold’s overview of Schrodinger wave mechanics: “What can be known about an electron, considered as a particle, is of a statistical nature, and is summarized in the behavior of a wave. When considering singlet substances, the normal Zeeman Effect occurs, providing the discrete values of the orbital angular momentum. In an attempt to rationalize the anomalous Zeeman effect, W. Pauli proposed the fourth degree of freedom of the electron which he called “two-valuedness not describable classically”.
This chapter examines the historical development of quantum mechanics, focusing on key experiments and theories that challenged classical physics. It begins with blackbody radiation, highlighting the discrepancy between classical predictions and experimental observations, leading to Planck's quantization hypothesis, which posits that energy is emitted in discrete packets (quanta). The chapter covers the photoelectric effect and Compton scattering, demonstrating wave–particle duality and validating quantum theory. It also discusses atomic models, culminating in the Bohr model and the energy-level diagram of the hydrogen atom, which explains atomic phenomena such as line spectra and discrete energy transitions. The chapter concludes by introducing the quantum model, which supersedes the Bohr model by incorporating wave–particle duality and the uncertainty principle, highlighting the necessity of quantum mechanics for accurate atomic-scale descriptions.
This chapter explores the foundational applications of quantum theory in the context of atomic physics. Beginning with the limitations of classical physics in explaining atomic phenomena, it introduces the quantum model of the atom, with particular emphasis on the Bohr model and its success in describing hydrogen spectra. The chapter then develops key quantum concepts such as quantisation of energy levels, wave–particle duality, and the Compton effect behaviour. Applications include the analysis of atomic emission and absorption spectra, the photoelectric effect, and X-ray production, all of which highlight the quantum mechanical understanding of matter and radiation. Through illustrative examples and problem-solving, the chapter demonstrates how quantum theory underpins modern atomic models and provides insight into the structure and behaviour of atoms.
We tried to introduce the idea of quantization in Chapter 9 as a completion of a one semester course. However, we skipped over some really interesting events in the history of Science between 1900 and 1913 when Bohr derived the quantized energy of the H atom. First we want to carry out the 1901 Planck derivation of the formula for blackbody radiation [1]. Many texts just show the curve, write e¼ hn, and move on. As a student, this author found that limited explanation very frustrating since energy quantization is a fundamental concept. Even among graduate texts in quantum mechanics, we are aware of only one that does the complete treatment which we will draw upon for the mathematics [2] but supplement with a narrative that we have found helpful to students over the years. Then in 1905, Albert Einstein (1879-1955), one of the most influential scientists of all time, gave an explanation of the photoelectric effect [3] for which he received the Nobel Prize in 1921. Even reducing our list to essential topics, we need to discuss the Davisson-Germer experiment [4]. The photoelectric effect introduces the idea that light waves can act as particles while the Davisson-Germer experiment showed that particles can act like waves and confirmed the De Broglie equation [5]. However, you can be assured that it will not be as difficult as you might have anticipated and if you can absorb the meaning of just these three key experiments you should be able to begin thinking in terms of quantum mechanics! Despite our slow historical development, this is 2010 and we have to get to the twenty-first century somehow!
The past two decades of attention to introductory physics education has emphasized enhanced development of conceptual understanding to accompany calculational ability. Given this, it is surprising that current texts continue to rely on the Bohr model to develop a flawed intuition, and introduce correct atomic physics on an ad hoc basis. For example, Halliday, Resnick, and Walker1 describe the origin of atomic quantum numbers as such: “The restrictions on the values of the quantum number for the hydrogen atom, as listed in Table 39-2, are not arbitrary but come out of the solution to Schrödinger's equation.” They give no further justification, but do point out the values are in conflict with the predictions of the Bohr model.