The electronic configuration of sodium atom is 2, 8, 1 and chlorine atom is 2, 8, 7. The atoms will form a bond by of electrons.
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The electronic configuration of sodium atom is 2, 8, 1, hence, it has 1 valence electron. Chlorine atom has 7 valence electrons and its electronic configuration is 2. 8, 7.
When sodium (Na) and chlorine (Cl) combine, the sodium atom loses an electron to form Na+, and the chlorine atoms gain an electron to form Cl−.
These oppositely charged ions are held together by the electrostatic force of attraction called ionic bond.