Final answer:
Sodium (Na) and chlorine (Cl) combine to form sodium chloride (NaCl), an ionic compound with unique properties distinct from both sodium metal and chlorine gas.
Step-by-step explanation:
When sodium (Na) and chlorine (Cl) chemically combine, they form sodium chloride (NaCl), which is best defined as an ionic compound. This is because it is composed of a metal, sodium (which forms sodium cations Na+), and a nonmetal, chlorine (which forms chloride anions Cl−), that combine in a 1:1 ratio. The properties of sodium chloride are vastly different from the individual properties of sodium and chlorine. For example, sodium alone is a highly reactive metal, while chlorine is a poisonous gas. However, when these two elements react, they form sodium chloride, a stable and essential compound for life that, instead of being reactive or poisonous like its constituent elements, dissolves safely in water.