Step-by-step explanation:
When sodium reacts with with chlorine atoms, an electrovalent bond is formed as a result of this interaction
The driving force for this interatomic interaction is the need for both sodium and chlorine to attain a stable electronic configuration. 
 
Sodium has one valence electron, Chlorine has 7 valence electrons. 
 Na = 2, 8, 1 
 Cl = 2, 8, 7 
 Sodium loses one electron as the less electronegative specie; 
 Na → Na⁺ + e⁻ 
 
 Chlorine then gains the one electron: 
 Cl + e → Cl⁻
Combine reaction;
 Na⁺ + Cl⁻ → NaCl
The Na transfers an electron to Cl and thereby becomes positively charged. The chlorine becomes negatively charged. The electrostatic attraction between the two develops the ionic bond.