αα\alpha means "proportional to" (the proportionality constant depends on the medium) rrr is the distance of separation. qqq is the charge of the ion ( only the magnitude of the charge is shown here.) kkk is the proportionality constant (Coulomb's constant). μμ\mu is the permanent dipole moment of the polar molecule (sections 8.7.4.2 and 8.8). From section 8.7 and 8.8 we treat define the dipole moment by the following equation