Question

Why are constituents of ionic compounds ions but in covalent compounds the constituent particles molecules?

Answer 1

Ionic compound form because of transfer of electron from one atom to other,this transfer of electron from one atom to other create ions and they will become the main constituents of an ionic compound.
Two or more than two atom when combined they will form molecule and ions are the charged atom.Charged atom means they accepted or donated electron.
Covalent compound formed by sharing of electron so they need molecule who can share there electron for formation of bond that's why constituent particle of covalent bond are molecule and they have all the fundamental properties of compound molecule.
Ionic compounds consist of ions of opposite charges held together by strong electrostatic forces, whereas pairs of electrons are shared between bonded atoms in covalent compounds.