Modern chemistry is built upon the foundations of quantum mechanics. This course aims to provide a solid understanding of the conceptual foundations and standard topics of quantum mechanics, while emphasizing its applications in chemistry. To achieve this, key topics—including the harmonic oscillator, angular momentum, spin, and hydrogen-like atoms—will be presented in conjunction with related chemical phenomena and the principles of spectroscopy. This knowledge serves as a vital foundation for a deep understanding of the electronic structures of atoms and molecules, chemical bonding, and the quantum theory of chemical reactivity, which will be covered in "Quantum Chemistry II."