Finding the Radius of a Thomson Atom in Relation to Hydrogen Atom Radius

[wumple]

Homework Statement

Assume that the density of positive charge in any Thomson atom is the same as for the hydrogen atom. find the radius R of a Thomson atom of atomic number Z in terms of the radius Rh of the hydrogen atom.

Homework Equations

The Attempt at a Solution

I don't know where to start...could someone give me a hint?

 

[Delphi51]

Write an expression for the charge density of a hydrogen atom (with an Rh in it). Set that equal to a similar expression for the charge density of an atom of atomic number z.