There is the hydrogen bomb and there is the nuclear weapon that uses plutonium. As far as I know the atomic structure of hydrogen versus plutonium are at the opposite ends of the chemical chart spectrum. Hydrogen having the least atomic weight of all elements and plutonium having a very high number of orbiting electrons. Can someone please help me to understand what it is that these two elements have in common that allow for nuclear fission to take place? Does anyone know what 'heavy water' is and how it is involved in the nuclear chain reaction creation? In the opposite energy producing activity of fusion, what is the cause of power generation? Is it always two hydrogen particles coming together to form helium? How does such action generate energy?