Download When Hard-Pressed, Hydrogen Becomes a Metal

When Hard-Pressed, Hydrogen Becomes a Metal
The most active metals are found in Group 1A. In
contrast to the other members of this group, hydrogen is typically a nonmetal. The very small size
of the hydrogen atom means that its electron is
bound quite firmly, and when hydrogen bonds to
other nonmetals, it typically does so by sharing
electrons rather than losing its electron to become
a cation. However, recent research indicates that
under extraordinarily high pressures, hydrogen
changes to a metal. Ho-Kwang Mao and R. J.
Hemley have performed experiments using a
diamond-anvil cell in which mechanical means are
used to produce millions of atmospheres of pressure in a tiny 20-m cell between two beveled,
gem-quality diamonds. These researchers found
that under 3 million atm of pressure, hydrogen
first assumes a solid phase that is transparent and
does not conduct electricity, and then it changes to
an opaque solid that conducts electricity like a
metal. There is a great deal of interest in this
metallic form of hydrogen because theory predicts
it should be a superconducting solid (zero resistance to current flow) at temperatures near 0°C,
much higher than the temperatures required for
any presently known superconducting material.
However, so far no conditions have been found
that stabilize the metallic form of hydrogen other
than extraordinarily high pressure. Researchers are
hoping that a way can be found to stabilize the
metallic hydrogen phase so that it persists under
less severe conditions. ■