Discuss the formation of the barium ion.
First, let's define ions. Ions are electrically charged particles which are formed when atoms gain or lose electrons. These losses or gains result in a complete highest energy level. As a result, they have the electronic structures of noble gases.
Let's also note what we know about metal atoms: that they form positive ions, meaning that they lose one or more electrons in their highest energy level.
With this in mind, let's consider Barium: Barium is a a part of group 2A. It is also a metal. Thus, given the above information, we can recognize that Barium has two electrons beyond the noble gas and that it will lose these two electrons. The result of this loss is that Barium becomes a 2+ ion with a noble gas configuration.
Barium can also release two electrons into the lattice as it participates in a metallic bond.