The hypothesis of indivisibility and structureless of atom reigned two thousands years. In XVII and XVIII centuries chemists were confirming this idea by showing that certain substances can not be subjected to further splitting into components via chemical methods. However, even Descartes imagined matter as infinitely divisible. At the end of the XIX century the first subatomic particle was discovered — electron, and at the beginning of XX century, physicists discovered the structure of the atom. About thirty years later, it became clear that one of the constituents of atom, its nucleus, can be divided into components — nucleons. After another thirty years in the experiments, it was revealed that the nucleons were also hiding constituents — partons, which later received the names of quarks and gluons. In addition, it was found that the electron is a member of the entire family of weakly interacting particles — leptons. Later physicists managed to systematize leptons and quarks in three generations and build a comprehensive theory of their interaction.