no rely if that's atom, you will discover it image in periodic table and that's for gratis. by fact with the aid of defination, the style of proton and electrons would desire to be equivalent in variety for an atom For ion, that's formed with the aid of the addition of subtraction of electrons from or to an atom. consequently, it ought to have cost (eg Ca^2+) For fomula unit, from the defination from wikipedia. that's the backside total variety ratio of ions represented in an ionic compound. Strickly talking, that's no longer "certainly one of those compound". for occasion, in a crystal of salt, there may well be billion of Na+ and Cl- ions exist in the crystal. even nonetheless, by fact the ratio of Na+ and Cl- is usually a million:a million. consequently, we write NaCl as a substitute of enable say "Na10000Cl10000. For polyatomic ions. From the call, all of us comprehend that "poly" advise "extra beneficial than one". consequently, that's a mix of two or extra atoms and incorporate cost. For molecules. with the aid of defination, a moleules can exist with the aid of its very own in environment. that's not comparable to ions. For ions, a cation (eg Na+) would nicely be exist on condition that a counterion exist (eg Cl-). even nonetheless, for a oxygen molecules for occasion (O2), it may exist with the aid of its very own. A molecule oftentimes does not have cost. Ionic compounds oftentimes style lacttice shape yet no longer molecules. even nonetheless, be careful that some atom would nicely be a molecule additionally. For noble gas, for an occasion, argon (Ar) can exist in atomsphere in its atomic style. consequently that's an atom and molecule concurrently.