含义Meaning
鲍林（1932）发现异核键 A–B 的键能比两同核键键能的平均值大，多出的部分 Δ（离子–共价共振能）随两原子吸电子能力差而增大，由此定义电负性差。规定 χ(F) = 3.98。
Pauling (1932) noticed that A–B bonds are stronger than the mean of A–A and B–B; the excess Δ (ionic–covalent resonance energy) grows with the difference in electron-attracting power and defines Δχ, with χ(F) = 3.98.
符号说明Symbols
| 符号Symbol | 含义 Meaning | 单位 Unit |
|---|---|---|
| \(D\) | 键解离能bond-dissociation energy | eV |
| \(\Delta\) | 额外离子共振能extra ionic resonance energy | eV |
推导Derivation
若 A–B 是纯共价键，其键能应为两同核键的平均（鲍林原取算术平均，后改几何平均）。
A purely covalent A–B would have the mean of A–A and B–B.
实测更大，差值 Δ 来自离子结构 A⁺B⁻ 的共振贡献。
The measured excess Δ comes from the ionic resonance structure.
经验发现 \(\Delta \propto (\Delta\chi)^2\)，单位 eV 时比例系数约 1（kJ/mol 时为 96.5）。
Empirically Δ ∝ (Δχ)², with coefficient 1 in eV.
适用条件与局限Assumptions & limitations
只给出相对值；电负性随氧化态、杂化变化（sp 碳比 sp³ 碳电负性大）。
Relative only; varies with oxidation state and hybridisation.
例题Worked example
H–F：D = 5.86 eV，H–H 4.52、F–F 1.66：Δ = 5.86 − √(4.52×1.66) = 3.12 eV → Δχ = 1.77（表值 3.98 − 2.20 = 1.78）。
H–F: Δ = 3.12 eV → Δχ = 1.77 (tables: 1.78).