Ask A Scientist© Chemistry Archive

name         Berndan R.
status       student
age          20s

Question -   Why does hydrogen turn in to metallic hydrogen?  Why
doesn't it just become solid hydrogen?
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Berndon :

          The term metallic refers to the type of bonding between individual
atoms, and is characterized by a material which conducts electricity rather
well. A material can have metallic properties as either a liquid or a
solid. For example, mercury is a liquid at room temperature and pressure,
yet it conducts electricity quite well. Copper, on the other hand, is a
solid at room temperature and pressure and also conducts electricity very
well. Both are metallic in this regard. If you put hydrogen under extremely
high pressures, the atoms are forced to become close together, and due to
the changes that this produces in electron energy states, it can be made
"metallic". If memory serves me correctly, almost all elements, including
hydrogen, can be compressed into a solid. Only helium cannot. This has to
do with a phenomenon called zero-point-energy and van der Waals forces. A
physicist can tell you more about this.

Jim Rubin
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When hydrogen is cooled to about 259 C. if freezes, forming solid
hydrogen, so it does "just become" solid hydrogen. However, if in addition,
the hydrogen is squeezed with a sufficiently high pressure, the electron
clouds are forced to overlap so that they are no longer confined to two
particular protons and instead form a continuous "sea" of electronic cloud.
At this point it becomes a conductor like other metals.

Vince Calder
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