定义Definition
熔点是在一定压强下（通常为 101.325 kPa）晶体的固态与液态平衡共存的温度。纯净晶体有确定的熔点，熔化时吸收热量而温度保持不变。
The melting point is the temperature at which the solid and liquid forms of a crystalline substance are in equilibrium at a given pressure, usually 101.325 kPa. A pure crystal has a sharp melting point; while melting it absorbs heat without its temperature changing.
与结构的关系Link to structure
熔化要克服粒子间的作用力。巨型共价结构（金刚石、SiO₂）和离子晶体（MgO、NaCl）熔点高；金属的熔点差别很大；分子晶体只需克服分子间作用力，熔点低。第三周期单质的熔点为：Na 98 °C、Mg 650 °C、Al 660 °C、Si 1414 °C、P₄ 44 °C、S₈ 115 °C、Cl₂ −102 °C、Ar −189 °C，峰值出现在巨型共价结构的硅。
Melting overcomes the forces between particles. Giant covalent structures (diamond, SiO₂) and ionic crystals (MgO, NaCl) melt high; metals vary widely; molecular crystals need only overcome intermolecular forces and melt low. The period 3 elements melt at Na 98 °C, Mg 650 °C, Al 660 °C, Si 1414 °C, P₄ 44 °C, S₈ 115 °C, Cl₂ −102 °C and Ar −189 °C, peaking at giant covalent silicon.
检验纯度Testing purity
杂质使熔点降低并使熔程变宽，所以测熔点可以检验有机物的纯度，并与文献值比较以鉴定化合物。把样品与已知纯品混合测熔点，若熔点不下降，两者为同一物质（混合熔点法）。
Impurities lower the melting point and widen the melting range, so measuring it checks the purity of an organic solid and, compared with literature values, identifies it. Mixing the sample with a known pure compound: if the melting point does not fall, they are the same substance (mixed melting point).
年表Timeline
- 1742
摄尔修斯以水的冰点和沸点为定点建立温标
Celsius bases his scale on the freezing and boiling points of water
- 约 1900
毛细管熔点测定法在有机化学实验中普及
The capillary melting-point method becomes standard in organic laboratories