# How many neutrons in an ""^238U atom?

Sep 11, 2017

In ""^238U........?
Well, for a start, the number of nuclear protons is $92$; i.e. for uranium, $Z , \text{the atomic number} = 92$ this is what defines uranium as an element.
Now the mass number is $238$, and therefore there are $238 - 92 = 146 \cdot \text{neutrons}$.
And finally the number of electrons, which is easy given what we know. We know we deal with a NEUTRAL element, and if $Z = 92$, the positive charge provided by the protons must be matched by an equal number of electrons, conceived to whizz around the nuclear core; i.e. there are 92 electrons..... The fissile isotope of uranium is ""^235U; how many neutrons in this nuclide?