. 2009 Sep 3;109(12):6858–6919. doi: 10.1021/cr900053k

Table 1. Selected Bonding Strengths.

Cation bonding strength (Lewis acid strength) and electronegativity in valence units from ref (1)
symbol	average observed coordination number	bonding strength	remarks
Cs⁺	9.2	0.109
Tl⁺	3−9	0.11−0.33	Lone pair
Rb⁺	8.0	0.124
K⁺	7.9	0.126
Na⁺	6.4	0.156
H₂O	2	0.2	Bonding through H
Ca²⁺	7.3	0.274
Mg²⁺	6.0	0.334
Al³⁺	5.3	0.57
Nb⁵⁺	6.1	0.82	d⁰ element
Si⁴⁺	4.0	1.00
Mo⁶⁺	4.9	1.23	d⁰ element
P⁵⁺	4.0	1.25
C⁴⁺	3.0	1.33
S⁶⁺	4.0	1.5
N⁵⁺	3.0	1.67
Cl⁷⁺	4.0	1.75

Anion bonding strength (Lewis base strength) in valence units
symbol	coordination number	bonding strength	remarks
ClO₄⁻	12	−0.08
NO₃⁻	9	−0.11
Br⁻	8	−0.12
VO₃⁻	7	−0.14	Polymeric tetrahedral coordination
Cl⁻	6	−0.17
SO₄²⁻	12	−0.17
Oxalate	12	−0.17
MoO₄²⁻	12	−0.17
H₂O	2	−0.2	Through O
CO₃²⁻	9	−0.22
F⁻	4	−0.25
PO₄³⁻	12	−0.25
SiO₃²⁻	7	−0.29	Chain
Si₂O₇⁶⁻	19	−0.32
BO₃³⁻	9	−0.33
SiO₄⁴⁻	12	−0.33
BO₄⁵⁻	12	−0.42
O²⁻	4	−0.50