Simple Molecular Lattices | 简单分子晶格

📚 Simple Molecular Lattices | 简单分子晶格

Simple molecular lattices are one of the four major structure types tested in Cambridge A-Level Chemistry. They consist of small discrete molecules held together in the solid state by weak intermolecular forces. Their properties contrast sharply with giant ionic, metallic, and covalent lattices, and many exam questions focus on explaining these differences in terms of bonding and structure.

简单分子晶格是剑桥 A-Level 化学考查的四大结构类型之一。它们由小的离散分子组成，在固态时通过微弱的分子间力结合在一起。其性质与巨型离子、金属和共价晶格形成鲜明对比，许多考试题目都要求从键合和结构的角度解释这些差异。

1. Simple Molecular Lattice: Definition and Examples | 简单分子晶格的定义与例子

A simple molecular lattice is a regular three-dimensional arrangement of small molecules. The particles occupying the lattice points are entire molecules, not atoms or ions. Examples include iodine (I₂), ice (H₂O), dry ice (CO₂), methane (CH₄), sulfur (S₈), phosphorus (P₄), and buckminsterfullerene (C₆₀).

简单分子晶格是小分子的规则三维排列。占据晶格点的粒子是整个分子，而不是原子或离子。例子包括碘（I₂）、冰（H₂O）、干冰（CO₂）、甲烷（CH₄）、硫（S₈）、白磷（P₄）和富勒烯（C₆₀）。

In these substances, strong covalent bonds hold the atoms together inside each molecule, but only weak intermolecular forces operate between neighbouring molecules. It is the weakness of these intermolecular forces that gives simple molecular solids their characteristic low melting and boiling points.

在这些物质中，强共价键将原子结合在每个分子内部，但相邻分子之间只存在微弱的分子间力。正是这些分子间力的微弱性，赋予了简单分子固体低熔点和低沸点的特征。

2. Intramolecular Bonds versus Intermolecular Forces | 分子内键与分子间力

Inside a molecule, atoms are joined by strong covalent bonds, with typical bond enthalpies ranging from about 150 kJ mol⁻¹ to 500 kJ mol⁻¹. Between molecules, the forces of attraction are much weaker, typically in the range 1–40 kJ mol⁻¹.

在分子内部，原子通过强共价键结合，典型的键焓约为 150 kJ mol⁻¹ 至 500 kJ mol⁻¹。在分子之间，吸引力要弱得多，通常在 1–40 kJ mol⁻¹ 范围。

This distinction is essential. When a simple molecular solid melts or boils, the molecules themselves remain intact; only the intermolecular forces are overcome. Covalent bonds inside each molecule do not break under normal melting or boiling conditions.

这一区分至关重要。当简单分子固体熔化或沸腾时，分子本身保持完整；被克服的只是分子间力。分子内部的共价键在正常熔化或沸腾

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