定义Definition
路易斯结构是用点表示价电子、用短线（或成对的点）表示共用电子对来描述分子或离子中原子成键情况的结构式。它显示了成键电子对和孤对电子，多数情况下各原子达到八隅体（氢为二电子）结构。
A Lewis structure shows the bonding in a molecule or ion using dots for valence electrons and lines (or pairs of dots) for shared pairs. It shows bonding pairs and lone pairs; in most cases each atom reaches an octet (two electrons for hydrogen).
画法Drawing one
数出全部价电子（阴离子加电子，阳离子减电子）；把电负性较小的原子放在中心，用单键连接各原子；把剩余电子作为孤对电子分给外围原子使其满足八隅体，再分给中心原子；中心原子不足八隅体时，把外围原子的孤对电子改为双键或三键。可用形式电荷判断哪种结构更合理。
Count all valence electrons (add for anions, subtract for cations); put the less electronegative atom in the centre and join atoms with single bonds; give the remaining electrons as lone pairs to the outer atoms to complete their octets, then to the central atom; if the central atom lacks an octet, turn outer lone pairs into double or triple bonds. Formal charges help choose the best structure.
例外Exceptions
缺电子：BF₃ 中硼周围只有 6 个电子。扩展八隅体：第三周期及以后的原子可以超过 8 个电子，如 PCl₅、SF₆。奇电子分子：NO、NO₂ 含未成对电子。电子离域的分子（如苯、O₃）需要用几个共振式共同描述。
Electron-deficient: boron in BF₃ has only six electrons. Expanded octet: atoms from period 3 onwards can exceed eight, as in PCl₅ and SF₆. Odd-electron molecules: NO and NO₂ have unpaired electrons. Molecules with delocalised electrons, such as benzene and O₃, need several resonance structures.
年表Timeline
- 1916
路易斯发表《原子与分子》，提出共用电子对成键
Lewis publishes The Atom and the Molecule, proposing the shared electron-pair bond
- 1919
朗缪尔推广并提出“八隅体”（octet）一词
Langmuir popularises the idea and coins the term octet
相关公式Formulas
例题Worked example
CO：C≡O 中 C 为 4 − 2 − 3 = −1，O 为 6 − 2 − 3 = +1。NH₄⁺ 中 N：5 − 0 − 4 = +1。
CO: C −1, O +1. NH₄⁺: N +1.