Ionic bonds are formed by the complete transfer of electrons from one atom to another.
Ionic bonds are formed between atoms that have an electronegativity difference greater than about 1.9.
The bond formation between sodium and chlorine, a metal and a non-metal.
The electronegativity values of sodium and chlorine are 0.9 and 3.0 respectively. This tells us that sodium has a low ionization energy and a tendency to give electrons while chlorine has a tendency to take electrons. When those two atoms come together under suitable conditions, to complete their octets, sodium gives one electron to chlorine.
11Na : 1s2 , 2s2 , 2p6 , 3s1
17Cl : 1s2 , 2s2 , 2p6 , 3s2 , 3p5
Sodium loses its valence electron and its electron configuration becomes identical to that of neon: 1s2 2s2 2p6. Likewise, the valence shell of chlorine becomes completely filled and its electron configuration resembles that of argon.
