Answer:
Valence electrons
Explanation:
Valence electron is the number of electrons in the outermost shell of an atom. Valance electrons are equal to the group number of the elements in the periodic table. For example, halogens are located in group 7 of the periodic table, and they have 7 valence electrons. Also alkali metals located in group 1 have 1 valence electron. In the formation of an ionic bond valence electrons are either lost or gained, and in covalent bonds valence electrons are shared.
