The ordinal number of a chemical element corresponds to the positive charge of the atomic nucleus, that is, to the number of protons contained in it. Since the atom is electrically neutral, it is obvious that the serial number of a chemical element also corresponds to the number of electrons that form the electron shell of the atom.
The number of the period in which a chemical element is located corresponds to the number of energy levels (electron layers) in the atom.
The group number corresponds to the number of electrons at the outer energy level of the atoms of the elements of the A-groups. That is, this constant is very important, because it expresses the magnitude of the nuclear charge.
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