工程與科技 大學 3年以上以前

不知道這題要怎麼計算..求解了謝謝

EXAMPLE 2.8 w Calculate the attractive force between a pair of Ba2+ and S2- ions that just touch each other. Assume the ionic radius of the Ba2+ ion to be 0.143 nm and that of the S2-ion to be 0.174 nm.