Molecular and Ionic Formula?

Question

OK, so I know how to tell if a formula should be molecular (covalent bond) or ionic from the word formula, but how do you tell if it is molecular or ionic from the short formula?

For example, would NO2 be nitrogen dioxide (molecular) or simply nitrogen oxide? I think it would be molecular because I think I did this one before, but I can't remember how to tell the difference.

Answer 1

Molecular formulas use the "Greek" naming system with "mono, di, tri" etc.

Almost always molecular formulas are composed of only nonmetals.

One exception would be the ammonium ion.  NH4^+

ammonium nitrate NH4NO3 is an ionic compound.

Other than that, most non-metal compound you'll study should be molecular.  SO2, SO3, CO2, N2O, CH4, etc, etc.

The first atom is not called "mono" if there is only one of those atoms.

NO is nitrogen monoxide

NO2 is nitrogen dioxide  (common name nitric oxide)

N2O5 is dinitrogen pentoxide.

N2O is dinitrogen monoxide  (common name nitrous oxide - laughing gas)

Usually the less electronegative atom is listed first (more electronegative atoms toward the upper right of the periodic table).

Hope that helps.

Answer 2

i think the difference will be in their electro negativity, you see, ionic bond   have always electronegativity of difference 1.7/1.8 but molecular doesnt look in such difference.. so firsly you should  see the difference in electronegativity between two elements.

Answer 3

As a fairly sound guide, two non-metals combining will do so via covalent bonding, while a metal and a non-metal will combine ionically.  So look to see where they are relative to each other on the Periodic Table: metals on the left; non-metals on the right.

(Though if the metal and non-metal are close together in the Periodic Table there could well be a fair degree of ionic character.)

Answer 4

The word formula and the short formula contain the same information. So you are quite right in thinking that NO2 is molecular (because of the small electronegativity difference between the two elements, or alternatively because it is a compound between two nonmetals). Nitrogen dioxide is indeed the correct name.