# Chemistry A-level question

I am a bit confused with these terms, are they the same or have I gone mad?
Is there a difference between mass to charge ratio (m/z) used in mass spectrometry and charge to size ratio (charge density) used to explain why +3 metal-aqua ions are more polarising than +2 metal-aqua ions?
Thank you, sorry for the wordy question.
Original post by student2876
I am a bit confused with these terms, are they the same or have I gone mad?
Is there a difference between mass to charge ratio (m/z) used in mass spectrometry and charge to size ratio (charge density) used to explain why +3 metal-aqua ions are more polarising than +2 metal-aqua ions?
Thank you, sorry for the wordy question.

Yes, there is a difference.

m/z = (relative mass of ion)/(charge on ion)

(Linear) charge density = (charge on ion)/(ionic radius)
(edited 1 year ago)
Original post by TypicalNerd
Yes, there is a difference.

m/z = (relative mass of ion)/(charge on ion)

(Linear) charge density = (charge on ion)/(ionic radius)

Thank you so much! Random question, what do you mean by linear charge density?
Original post by student2876
Thank you so much! Random question, what do you mean by linear charge density?

Linear charge density is simply the ratio of the ion’s charge to its radius.

‘Charge density’ is more accurately defined as the ratio of an ion’s charge to its volume. Because the volume of an ion is (4πr^3)/3, you could say that the charge density is inversely proportional to the radius cubed, or CD α 1/r^3 (where CD is short for charge density).

As r increases, both the charge density and linear charge density will decrease, so both are useful measures of how polarising an ion is.

In summary, linear charge density is easier to work with compared to charge density, hence why I gave the definition of linear charge density in my first post.
(edited 1 year ago)