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The state of a substance—whether it is a gas, liquid, or solid—depends on both pressure and temperature. To standardise comparisons, scientists use a set of reference conditions: a temperature of 0 °C (32 °F) and a pressure of 1 atm. Under these conditions, the phase of most elements is fixed: some are solid, while others remain gaseous or liquid.
When a material changes from solid to liquid, it is said to melt; when it changes from liquid to solid, it freezes. The freezing point and the melting point are identical, differing only in the direction of the transition. A solid is found at temperatures below its freezing point, while a liquid or gas exists above the melting point.
At standard temperature and pressure (STP), the following elements remain gaseous or liquid and therefore have freezing points below 0 °C:
All other elements are solid at STP, meaning their freezing points exceed 0 °C.
