When atoms combine with each other to form compounds, the process is called bonding. Atoms do this in order to achieve the stability of the closest Nobel gas (a full outer shell of electrons). Metals have only a few electrons in their outer shell (1-3) so they will readily lose these electrons to attain the electronic configuration of the closest Nobel gas.

For. eg, Lithium has an electronic configuration of 2,1. Lithium will lose its single outer electron to form a lithium ion resulting in an outer shell of 2 electrons (remember the first electron shell has a maximum capacity of 2 electrons). Hence the lithium ion produced will have a full outer shell with the electronic configuration of helium (closest nobel gas).

The opposite is true for non metals; they have many electrons in their outer shell and will readily gain or share electrons to achieve the stability of a full outer shell (electronic configuration of the closest nobel gas).

You may be wondering why non metals cannot lose all of its outer electrons; or why metals can’t gain numerous electrons to complete its outer shell. The answer is simple – energy. It is far too energy consuming for non metals to lose all its outer electrons and for metals to gain electrons to complete their outer shell. The energy we are considering here is the energy needed to overcome electrostatic forces of attraction. You will learn about this further in your studies.