The periodic table or periodic system is a scheme that shows the structure and arrangement of chemical elements according to a law of periodicity, which is that "the properties of the elements are a periodic function of their atomic numbers . "
In this way, all chemical elements are arranged in increasing order of their atomic number, which represents the number of protons in the nucleus of their atom and, consequently, the number of electrons found in the corona.
According to the above, each element has one more proton and one electron than the one before it. That is, the electronic structure of an atom is exactly the same as that of the element that comes from it, differing only in the last electron. All elements that have the same number of electrons, in their outermost shell, will have similar chemical properties.
From the beginning of the modern era of Chemistry, the ordering of known elements was a great concern of researchers, in order to relate their properties, among the leading scientists we have Johann Wolfgang Döbereiner, John Newlands, Dmitri I. Mendeleev and Julius Meyer, the latter two independently developed the periodicity law, achieving the same results.
The periodic table is made up of periods, which are the horizontal rows of it, where the elements have different physical and chemical properties. There are seven periods; the first three shorts, the next three longs and the seventh is incomplete. Within the 6th and 7th period the so-called Lanthanide and Actinide elements are located .
There are also groups or families, a set of certain elements that have similar properties. There are 18 groups represented by each of the columns in the table.
They are grouped into two sets, those of type A (groups 1, 2, 13 to 18): group IA (alkali metals), IIA (alkaline earth metals), IIIA (earths), IVA (carbonids), VA (nitrogenoids), VIA (chalcogens or ampigens), VIIA (halogens) and VIIIA (noble gases), which are called the representative elements; and elements of type B (groups 3 to 12), called transition elements.
