It is expedient to speak about metal and nonmetallic properties of substance in connection with the Periodic Table. Mendeleyev's table establishes dependence of chemical properties of elements on a charge of their atomic nucleus.
All elements of a periodic system are divided into metals and nonmetals. Atoms of metal have small quantity of electrons at the external level which are kept by a kernel attraction. The positive charge of a kernel is equal to quantity of electrons at the external level. Communication of electrons with a kernel rather weak therefore they easily separate from a kernel. Metal properties are characterized by ability of atom of substance to easily give electrons from external level. The top horizontal row designated by the Roman figures shows quantity of free electrons in periodic Mendeleev's system at the external level. In the periods with I on III metals are located. With increase in the period (increase in quantity of electrons at the external level) metal properties weaken, and nonmetallic properties amplify. Vertical rows of the table of Mendeleyev (groups) show change of metal properties depending on substance atom radius. In group from top to down metal properties amplify because the radius of an orbit of the movement of electrons increases; from it communication of electrons with a kernel decreases. The electron at the last level in this case very easily separates from a kernel that is characterized as manifestation of metal properties. Also number of group indicates ability of atom of substance to attach atoms of other substance. The ability to attach atoms is called valency. Accession of atoms of oxygen is called oxidation. Oxidation is manifestation of metal properties. It is possible to identify by number how many atoms of oxygen metal atom can attach: the more atoms joins, the metal properties are stronger. All metals have similar properties. All have a metal gloss. It is explained by reflection of any light electronic gas which is formed by the free electrons moving between atoms in a crystal lattice. Existence of free mobile electrons gives property of conductivity of metals.