# Calculating charge density of an atom

1. Aug 29, 2011

### mitch_1211

here I am only considering the charge density of the nucleus, i.e the density of protons.

I know that from mass density i have rho = m/v -> v = m / rho
I'm not sure what mass to use here. Molecular weight? molar mass? where does avagadros number come into it?

then is it simply charge density = q/v

Will the volume calculated from v = m / rho differ from using 4/3 pi r^3 the volume of a sphere?

A little confused on which approach to use.

Mitch

2. Aug 30, 2011

### JeffKoch

Charge density implies charge per unit volume, which in your case is the total charge in the nucleus (depends on which nucleus you are talking about) divided by the volume of said nucleus, which ultimately is a meaningless quantity but nevertheless can be approximated depending on what property of it's "volume" you care about. Where do you think mass and avogadro's number come into this?

3. Aug 30, 2011

### mitch_1211

I think i will need avogadros number when calculating the volume from v = m / rho not sure if i need to use molar mass, atomic weight here