Table 1.

Unhydrated radius, self-energy, image charge potential, and hydrogen-bond perturbation energy of various ions.

ion species	unhydrated radiusa [Å]	self-energy in bulka [kBT]	image charge potential at the interfaceb [kBT]	hydrogen-bond perturbation energyc [kBT]
Na+	0.95	−3.66	1.83	0.43
K+	1.33	−2.61	1.31	1.18
NH4+	1.48	−2.35	1.17	1.62
F−	1.36	−2.56	1.28	1.26
Cl−	1.81	−1.92	0.96	2.96
Br−	1.95	−1.78	0.89	3.71
I−	2.16	−1.61	0.80	5.04
NO3−	2.64	−1.32	0.66	9.20

^aUnhydrated radius is from the book by J. Israelachvili⁶⁵ and ion’s self-energy was calculated with water dielectric constant ε_water ~ 80.

^bFrom the equation by L. Onsager et al.⁴⁴ at the distance of ion’s unhydrated radius and at infinite dilution.

^cFrom hydrogen-bond perturbation energy 0.5 k_BT/Ų by Y. Levin⁵⁴.