The main quantum number is an integer which is definition of a condition of an electron at the power level. Power level is a set of stationary conditions of an electron in atom with close values of energy. The main quantum number defines remoteness of an electron from a kernel, and characterizes energy of electrons which occupy this level.
Set of numbers which characterize a condition of an electron are called quantum numbers. Wave function of an electron in atom, its unique state is defined by four quantum numbers – the main thing, magnetic, orbital and a spleen – the magnetic moment of the movement of an elementary particle expressed in quantitative value. The main quantum number has designation n. If the main quantum number increases, then both the orbit, and energy of an electron respectively increases. The value n is less, the value of power interaction of an electron with a kernel is more. If total energy of electrons is minimum, then such condition of atom is called unexcited or the main. The condition of atom with high value of energy is called excited. At the power level the largest number of electrons can be determined by formula N = 2n2. When there is a transition of an electron from one power level to another, also the main quantum number changes. In the quantum theory the statement is accepted that energy of an electron is quantized, that is can accept only discrete, certain values. To know a condition of an electron in atom it is necessary to consider energy of an electron, a form of an electronic cloud and other parameters. From area of natural numbers where n can be equal 1 and 2, and 3 and so on, the main quantum number can accept any value. In the quantum theory the power levels designate by letters, value n - numbers. Number of the period where there is an element, is equal to number of power levels in the atom which is in the main state. All power levels consist of subtotals. The subtotal consists of atomic orbitals which are defined, characterized by the main quantum number n, orbital number l and quantum number of ml. The number of subtotals of each level does not exceed value n. The wave Schrödinger equation is the most convenient description of the electronic structure of atom.