Book: Introduzione alla fisica atomica

Scope and Aim
Introduzione alla fisica atomica, authored by Enrico Fermi in 1928, offers a compact and systematic introduction to atomic physics as it stood at the end of the old quantum era. The text aims to equip students with the experimental facts, the conceptual tools, and the mathematical methods needed to follow contemporary theories of atomic structure and spectra. Emphasis falls on clear exposition and practical calculation rather than on philosophical debate.

Classical Foundations and Experimental Background
The book begins by grounding atomic theory in the wealth of experimental evidence available at the time: scattering experiments, spectral series, X-ray data, and effects of external fields. Fermi reconstructs the problem facing physicists by showing how classical electrodynamics and mechanics fail to account for discrete spectral lines, stability of atoms, and radiation phenomena. This empirical orientation establishes why new, nonclassical assumptions about electrons and energy levels became necessary.

Bohr-Sommerfeld Theory and Atomic Models
A central portion of the text develops the Bohr model and its Sommerfeld extensions with mathematical clarity. Quantization conditions, orbital angular momentum rules, and the calculation of energy levels receive step-by-step treatment, with hydrogen and hydrogen-like ions treated as paradigmatic examples. Fermi demonstrates how relativistic corrections and elliptical orbits explain fine structure, and he shows the practical use of quantization rules for multi-electron approximations where possible.

Spectral Phenomena and Perturbations
Spectroscopy forms a recurring thread, and the connection between quantized energy differences and observed spectral lines is made explicit through worked examples. The book examines fine and hyperfine splitting, Zeeman effects, and selection rules as consequences of orbital structure and perturbations. Transition probabilities and intensity considerations are discussed in relation to emission and absorption processes, providing students with tools to connect theory to measured spectra.

Quantum Principles and Emerging Ideas
While rooted in the old quantum theory, the text acknowledges and incorporates the newer conceptual advances of the mid-1920s where appropriate. The role of quantization rules, correspondence principles, and conservation laws receives careful analysis, and Fermi treats the conceptual shift toward a discrete description of atomic phenomena with both rigor and restraint. Mathematical derivations are presented so the student can see how formal rules arise from empirical constraints and theoretical symmetries.

Pedagogy and Legacy
Fermi's style combines concise mathematical derivations with physical intuition, making technical topics accessible without sacrificing precision. Worked calculations, illustrative problems, and a disciplined emphasis on the relation between observation and theory characterize the instructional method. The book became an influential teaching resource in Italy and beyond, appreciated for its clarity and for providing a solid grounding that prepared students to engage with later developments in quantum mechanics and atomic physics.