In terms of gaining or losing electrons, the elements of the periodic table are classified into three categories: inert gases, nonmetals and metals. Generally, inert gases do not readily gain nor lose electrons, while nonmetals are more likely to acquire electrons. Metals contain low ionization energies, which refer to the amount of energy required to free or remove an electron. These elements also have low electron affinities, or the attractive forces between an incoming electron and the nucleus of an atom. The lower the ionization energies and electron affinities of an atom are, the greater the tendency to lose electrons.
On a periodic table, ionization energy increase as one moves from left to right across a row. Elements found on the left side of this table have much lower ionization energies than those on the right. Likewise, elements on the right side tend to gain electrons. These elements are generally nonmetals.
In reactions between metals and nonmetals, the number of electrons lost by a metal will depend in which group it is in. For example, metals in group 1A will lose one electron from its valence shell, while a metal in group 3A loses three electrons. Alternatively, nonmetals in group 5A gain three electrons because they have five electrons in the valence shell.Learn more about Atoms & Molecules