Question

why do we call sodium chloride rathar than chloride sodium?​

Answer 1

Sodium chloride, regular table salt, is also known as the mineral halite. The diagram to the right shows how sodium and chlorine atoms pack tightly together to form cube-like units of the compound NaCl. Crystals of table salt imitate this structure-they're shaped like little cubes.

Answer 2

Sodium chloride is taken as typical of ionic compounds, and is chosen rather than, say, cesium chloride, because it is found on every syllabus at this level.