CHEMISTRY COMMUNITY

If a compound has a linear shape, how do you determine polarity or non-polarity? Is there a sure fire method?

For example, if there is a positive charge on the central atom, and a negative charge on one bonded atom does that mean those charges cancel each other regardless of another atom attached to the central atom without a pull on it?

Basically, you want to look and see if the dipole moments cancel out. You can definitely look at the charges, which means you are looking to see whether there are lone pairs on the central atoms or there exists a lack or abundance of lone pairs from the outer atoms that make the outer atoms have a positive or negative charge.

But I would also simply consider the electronegativity of each atom. In a linear model, there's always going to be a sort of X--A--X, where the X can be the same or different. I would first start off by seeing the relationship between the X--A's. If the dipole moment is going towards the X from the central atom in both bonds, then it would be a nonpolar molecule. That's actually the only case where it would be nonpolar, because if the dipole moment shows that X is going towards A and/or only one bond shows that the dipole is going to the X from the central atom, then there's a dipole moment, meaning that it's a polar molecule.

I understand that I am close to incoherency as it's pretty late at night, but TL;DR: There's no surefire way. You have to look and see if dipoles cancel using electronegativity.

I hope this helped and answered your question!