The radii of an atom is difficult to quantify because electrons move towards and away from the nucleus (in electron clouds). The nucleus also does not have a defined boundary, but the radius can be approximated by:

\(R = 1.25 \cdot A^{\frac{1}{3}} \; [fm]\)

A femtometer is \(1 \; [fm] = 10^{-15} \; [m]\)

Thus, the volume of the sphere increases proportionally to the atomic mass. The ratio \( V/A\) is also constant suggesting the density is uniform like a liquid drop (i.e., the liquid-drop model). .

The radius of an unknown nucleus is determined to be twice a large as another. What is the ratio of their masses?