How to Calculate How Many More Neutrons U-238 Has Than U-235

Protons, neutrons and electrons make up each atom of an element. Picture a pomegranate surrounded by a cloud of buzzing gnats. An atom's protons and neutrons are packed together in its center, or nucleus, like the seeds of a pomegranate, and the electrons whiz around the nucleus in a blurred cloud of possible positions. The atoms of one element always have the same number of protons, but if they are isotopes, they may have different numbers of neutrons. Uranium-238 (U-238) and uranium-235 (U-235) are isotopes of uranium.

Instructions

1. • 1

     Write the names of the two uranium isotopes of you want to analyze. For example, write "U-238, U-235."

   • 2

     Circle or underline the number in each isotope's name. This is the isotope's atomic mass, which is approximately the number of protons and neutrons in one atom of the isotope.

   • 3

     Find the difference of the atomic-mass numbers of the two uranium isotopes. For example, subtract 235 from 238, which equals 3. This tells you U-238 has three more neutrons than U-235.