The representative particle for salt, or sodium chloride (NaCl), is the formula unit. This term refers to the simplest ratio of the ions in the compound. In the case of NaCl, it consists of one sodium ion (Na+) and one chloride ion (Cl–), making the formula unit NaCl.
To understand why the formula unit is the representative particle in this context, it’s important to consider that NaCl is an ionic compound. Ionic compounds do not exist as discrete molecules; instead, they form a lattice structure that is extended throughout the solid. Each formula unit represents the ratio of ions in this lattice. Therefore, when discussing salts like NaCl, using the formula unit helps to simplify and accurately convey the composition of the substance.