the early nineteenth century, scientists began to tidy up the increasing amount of information they had available. In 1869, these efforts culminated in the 'development of what today is called the periodic law, which states that certain physical and chemical properties to express themselves at regular intervals when the elements are arranged in order of increasing atomic number.
Frequency In chemistry, Law which states that the chemical and physical properties of the elements recur in a systematic way for atomic numbers increasing. In the periodic table the elements are distributed according to the external electronic configuration. In particular, see the table in vertical position (for groups), we find elements that have the same number of electrons nell'orbitale outside, and for this reason they have similar physical and chemical characteristics. Instead of moving in a horizontal direction, ie by reading the table for periods, we find that electrons in atoms present nell'orbitale outer rise, continuously, from 1 to 8. When a period is completed, it will start a new one, so that the configurations external electronic, and with it the chemical properties of elements change periodically repeating line by line (ie, period by period). Adjacent elements within a period, therefore, have an electronic structure that varies regularly through it and therefore are characterized by a parallel change of ownership. The most important periodic properties: atomic radius, ionization, electron affinity and electronegativity. More precisely, the atomic radius increases moving in the periodic table from top to bottom, ie in individual groups and decreases from left to right, ie in each period. The first ionization energy, the affinity Electronic el'elettronegatività increase from left to right in the periodic table, but decrease from top to bottom.
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