Why some compound do not have molecular formula?

Answer 1

Once you get into the realm of compounds you are really looking at two types---ionic and molecular. Molecular compounds are made up of all the same type of molecule, and those molecules consist of a series of atoms covalently bonded together. The molecular formula of a molecular compound gives the number of each type of atom that makes up the molecule. Ionic compounds are different---there are no definable molecules present, just lattices of alternating positive and negative ions (charged atoms). So unlike molecular compounds there is no definable subunit in an ionic compound. Instead ionic compounds are represented by the simplest ratio of ions in the compound. For instance, in table salt there is one sodium ion per chlorine ion so the formula is NaCl. that does not mean there are little NaCl molecules making up the compound, just that the ratio of those two ions is 1:1. In calcium chloride there are two chloride ions for every calcium ion, so its formula is CaCl2. So the simple answe to the question is that molecular formulas are not used for ionic compounds because they are not comprised of molecules. That does not keep people (even chemists) from referring to the formulas of ionic compounds as "molecular formulas" but it is technically a misnomer. Simply calling them "formulas" or "ionic formulas" would be more appropriate.

Answer 2

An ionic compound cannot be represented by a molecular formula because it is not made up of molecules.

Answer 3

An ionic compound cannot be represented by a molecular formula because it is not made up of molecules.

Answer 4

Ionically bonded compounds do not have true molecules and therefore do not have molecular formulas.