Melting point: definition in chemistry
Melting point: The temperature at which a solid turns into a liquid at a given pressure. For a pure substance it is the same as the freezing point.
At the melting point, solid and liquid can exist together, and added heat goes into breaking down the solid's structure rather than raising the temperature. Pure crystalline substances melt sharply at a fixed temperature, while impurities lower the melting point and spread it over a range, so chemists use melting points to check purity. Melting points reflect how strongly particles are held together: ionic and giant covalent solids melt at much higher temperatures than molecular solids.
Examples
- Ice — 0 °C
- Gallium — about 29.8 °C, so it can melt in the palm of a hand
- Table salt (NaCl) — 801 °C
- Tungsten — 3,422 °C, the highest of any metal
On the periodic table
Melting points tend to peak toward the middle of each period, at giant covalent elements such as carbon and silicon or at transition metals such as tungsten, and are lowest for the noble gases.