Olympia Brown from Royal institute explains what happens to substance at change of a phase on the example of Hydrargyrum. And even if you know thermodynamics by heart, it is always interesting to look at the hammer made of the cooled Hydrargyrum.
Hydrargyrum — perhaps, the most convenient material for a visual aid on thermodynamics. At easily accessible temperatures it can be both fluid, and solid, and gaseous. However, the same can be told also about water, but to watch Hydrargyrum much more interestingly.
At ambient temperature (and in the range from 357 to -39 °C) Hydrargyrum fluid. separate atoms of metal have such high energy that constantly move as molecules of fluid water move. Energy of some of them is so high that they turn from the surface of liquid into gaseous state, forming toxic fumes.
If to look at the place of Hydrargyrum in Mendeleyev’s table, mobility of its atoms will speak simply: at an element with ordinal value 80 the external electronic shell is completely filled. Therefore atoms of Hydrargyrum are stable and hardly form among themselves loose couplings which are necessary for existence of a crystal lattice of metal.
If temperature of metal falls below fusion point (-38,83 °C), Hydrargyrum begins to behave as all other metals — becomes solid. At the same time atoms in it slow down the driving and are built in a crystal lattice.