. 2015 Jun 16;108(12):2886–2895. doi: 10.1016/j.bpj.2015.05.006

Table 1.

X-ray scattering contrasts and sizes of ions in water

	Z_I	V_I (Å³)^a	Z_eff^b	R_M−O (Å)^c
Cl⁻	18	40.2	4.6	–
Na⁺	10	−12.6	14.2	2.3
K⁺	18	4.3	16.6	2.8
Rb⁺	36	12.8	31.7	2.9
Cs⁺	54	24.7	45.8	3.1

The absolute limiting partial volume per ion (±1 Å³), from Marcus (40).

Calculated from Eq. 2 (±0.4e⁻).

Distance between the ion and the first hydration shell, from Marcus (41).