Why do sodium and chlorine become oppositely charged ions in table salt?

In sodium chloride, sodium and chlorine form oppositely charged ions through the transfer of an electron to achieve a stable, closed outer shell configuration, often referred to as the octet rule.12

The process occurs because:

• Electron Transfer: A sodium atom has a single electron in its outermost shell. By donating this electron to a chlorine atom—which needs one electron to complete its own valence shell—both atoms attain a stable, closed-shell structure.13
• Ion Formation: Once the electron is transferred, the sodium atom becomes a positively charged cation (Na⁺), and the chlorine atom becomes a negatively charged anion (Cl⁻).1
• Lattice Energy: While the initial ionization requires an input of energy, the formation of a crystalline array releases a large quantity of energy known as lattice energy. This strong electrostatic attraction between the resulting oppositely charged ions stabilizes the compound, making the solid state lower in energy than the individual elements.45