Hello aspirant

Formation of sodium chloride can be understood as this:-

The electronic configuration of sodium is 2,8,1 i.e  it has only one electron in its outermost shell. So, it will donate one electron to form a sodium ion i.e. Na+.

The electronic configuration of chlorine is 2,8,7 i.e it has 7 electrons in the outermost shell and it needs one more electron to achieve stable electronic configuration. So, a chlorine atom takes one electron to form a negatively charged chloride ion i.e. Cl-

When sodium reacts with chlorine, it transfers its one outermost electron to the chlorine atom. By losing one electron, sodium atom forms a sodium ion (Na+) and by gaining one electron, the chlorine atom forms a chloride ion (Cl-).

Sodium ion has positive charge whereas chloride ions have negative charge. Due to opposite charges, sodium ion and chloride ions are held together by the electrostatic force of attraction to form sodium chloride, Na+Cl- or NaCl.

In sodium chloride compound, the electronic configuration of sodium is 2,8 which resembles with neon inert gas and the electronic configuration of chloride ion is 2,8,8 which resembles with argon inert gas. Due to this, sodium chloride compound is very stable.

Hope this helps