Electrostatic force arises due the charges at rest.In a isolated atom there is three fundamental particles called electron,proton and neutron.the electron is negatively charged,proton is positively charged and the neutron is neutral.
Generally the force between electron and proton is attractive,there will be also repulsion between proton and proton.due to the strong nuclear forces atom main its stability In an stable atom the the neutron to proton ratio lies between 1 to 1.42.if the number of neutrons are increased more,the stability will be hampered resulting the decrease in nuclear force also.
As neutron is neutral,there will be no change in the electrostatic forces as there is no increment of charge.but when the neutron number is increased at that time the binding energy per nucleon is decreased which in turn affects the nuclear force which is a short range force.the nucleus becomes heavy and unstable which undergoes decay.
one thing we have to remember also that the nuclear force is spin dependent .so the change in neutron number affects the strong nuclear force which is the reason for its decrement.
