hichem belarbi

This chapter provides a comprehensive and structured introduction to the fundamental concepts of atomic and molecular chemistry, adopting a historical and pedagogical approach. It begins with an exploration of atomic structure, from the discoveries of Democritus to Rutherford's nuclear atom model and Schrödinger's quantum mechanics. The document details the constituents of the atom (protons, neutrons, electrons), their characterization (atomic number, mass number, isotopes), and associated quantities such as molar mass and Avogadro's number. It then presents Bohr's model for the hydrogen atom, electronic transitions, spectral series, and the Rydberg-Balmer equation. The complexity of polyelectronic atoms is subsequently addressed by introducing key concepts such as the screening effect and effective nuclear charge, calculated using Slater's rules. The second part of the chapter focuses on chemical bonding. It begins with the Lewis model, its rules (duet and octet) and limitations, then explores molecular geometry via Gillespie's VSEPR model. Finally, the document presents more advanced models: valence bond theory and atomic orbital hybridization ($sp$, sp2, sp3, etc.), as well as molecular orbital theory (LCAO) to explain the formation of $\sigma$ and $\pi$ bonds, bond orders, and the magnetic properties of molecules. Each section is enriched with examples, solved exercises, and summary tables, linking the concepts to concrete applications.

Keywords: Atomistic, Atomic Structure, Quantum Mechanics, Bohr Model, Electronic Configuration, Periodic Table, Chemical Bonding, Lewis Structures, VSEPR Theory, Hybridization, Molecular Orbitals (LCAO), Effective Nuclear Charge, Spectroscopy, Stoichiometry.