Question

what is the electrostatic potential energy (Eel) of the ionic bond between a Ca2+ ion and a S2- ion? Before doing the calculation, predict whether the result you get will be less than (more negative) than the Eel value for KCl (-7.24x10-19J)

Answer 1

I think the value of electrostatic potential energy of calcium sulfide CaS formed will be less(more negative) than KCl because the Ca2+ and S2- ions has more charge that is +2 and -2 respectively when compared to Kcl which has +1 and -1 charge.so it will be more negative .we know electrostatic potential energy= (k*q1*q2)/(r(cation)+r(anion)).

so the negative value will be more for CaS and radius of CaS is less than KCl as available from radius data.(note: radius value has not been given so standard value is considered).

electrostatic potential energy of CaS= (K*q1*q2)/(r(Ca2+ion)+(r(s2-ion))= (2.31 * 10^-28*(2*-2))/((0.99+1.84)*10^-10)m(unit for raduis).

k=2.31*10^-28

we get Eel= 3.26*10^-18J for CaS which is less than -7.24*10^-19(KCl) as predicted.