When Na and Cl atoms combine to form NaCl, they undergo ionic bonding. In ionic bonding, electrons are transferred from one atom to another, resulting in the formation of positively charged ions (cations) and negatively charged ions (anions). In the case of NaCl, sodium (Na) atom loses one electron to chlorine (Cl) atom, resulting in the formation of sodium cation (Na+) and chloride anion (Cl-). These oppositely charged ions are then attracted to each other by electrostatic forces, forming an ionic bond. The resulting compound, NaCl, is an ionic compound held together by the strong electrostatic attraction between Na+ and Cl- ions.