In chemistry, valence electrons are called electrons located on the outer (valence) shell of an atom . Valence electrons determine the behavior of a chemical element in chemical reactions , that is, they take part in the formation of a chemical bond , and completes the electron layer of the atoms participating in it. The less valence electrons an element has, the easier it gives these electrons (exhibits the properties of a reducing agent ) in reactions with other elements. And vice versa, the more valence electrons are contained in an atom of a chemical element, the easier it gets electrons (exhibits oxidizing properties) in chemical reactions, all other things being equal. Fully filled external electron shells have inert gases that exhibit minimal chemical activity. The frequency with which the outer electron shell is filled with electrons determines the periodic change in the chemical properties of the elements in the periodic table.
The number of valence electrons (maximum valency ) is equal to the group number in the periodic table in which the chemical element is located (except for subgroups).