Ion
Ionic radius (Å)
Hydration free energy in kJ mol−1 (kcal mol−1)
Li+
0.60
−410 (−98)
Na+
0.95
−301 (−72)
K+
1.33
−230 (−55)
Rb+
1.48
−213 (−51)
Cs+
1.69
−197 (−47)