Understanding the nature of the world requires improving our knowledge of the microworld. In this regard, the book gives a fairly comprehensive understanding of the basics of the atom, its structure, and spectral characteristics. The book consistently describes historical experiments with appropriate visual illustrations that help to better understand the development of ideas about the atom. The book contains information about the most basic models of the structure of atoms, ranging from the planetary model of the structure of the atom according to Rutherford, and ending with the basics of quantum theory, which is still relevant today. It is known that atoms can interact with each other, forming more complex structures - molecules, and knowledge about the type of chemical bond between atoms in a molecule is an important aspect in studying the structure of matter and predicting their chemical and physical properties, that can be gained through a logically structured information in the book. Importantly, the book discusses advanced methods for studying matter at the atomic level, including various types of scanning microscopy, X-ray crystallography, nuclear magnetic resonance and mass spectrometry. The book will be useful both for those who wish to deepen their knowledge about the atom, the regularities in changing the properties of an atom in the periodic table, modern research methods, and those who are interested in the nature of the world, especially on a nanometer scale.