Contents   1 Characteristics        2.Properties of the electron            3.  History of discovery              4.Mendeleev                   5.Structure of the periodic system                      6.Groups                          7.Periods                               8.Blocks                                   9.Other periodic patterns                                     10.Literature                                       Atom (from the Greek atomos - indivisible) - mononuclear, chemically indivisible particle of a chemical element, the carrier material properties. Substances consist of atoms. The atom itself consists of a positively charged nucleus and the negatively charged electron cloud. In general, the atom is electrically neutral. Size of the atom is completely determined by the size of its electron cloud, since the size of the nucleus is negligible compared to the size of the electron cloud. The core consists of positively charged protons Z (proton charge corresponds to 1 in arbitrary units) and N neutrons, which do not carry a charge (protons and neutrons are called nucleons). Thus the nuclear charge determined only by the number of protons and atomic number is equal to the periodic table. Positive charge of the nucleus is compensated by negatively charged electrons (electron charge -1 in arbitrary units) that form the electron cloud. Thus the number of electrons equal to the number of protons. The mass of protons and neutrons are (respectively 1 and 1 amu). Determine the mass of the atomic mass of its nucleus, because the electron mass is about 1850 times smaller than the mass of the proton and neutron, and rarely taken into account in the calculations. The number of neutrons can be found from the difference between the mass of the atom number of protons (N = AZ). Kind of atoms of a chemical element with a nucleus consisting of a well-defined number of protons (Z) and neutrons (N) is called a nuclide