And the reason why bombs have more of the U-235 is because is splits easier than U-238, so it's easier to end up with a self sustaining chain reaction, where ev

And the reason why bombs have more of the U-235 is because is splits easier than U-238, so it's easier to end up with a self sustaining chain reaction, where every U-235 that splits produces enough neutrons to split off two more U-235 atoms, which in turn splits 4, then 8, then 16 and so on - the chain reaction splits the whole lot all at once and you've got a bomb.