However this is not a stable atom, because the outer shell called the valence shell is not FULL to its max capacity of 8. So for Na the valence number is 1. The valence number is the number of unpaired electrons in the outer shell. Another issue we will study is stability of atoms. The stability of an atom is the state in which the atom is usually found.
Atoms always try and exist in a state in which the outer shell is full with electrons.
They do this by forming bonds with other atoms of other elements to give compounds, example Na bonds with Cl to give NaCl. This is an ionic bond because there is no sharing of electrons.