There are more than 100 substances listed in the Periodic Table of the Elements. This table is called “periodic” because, although each column is completely different, the properties of one row are very similar to the properties of the next. If you start on the left with an alkali metal, and you go through a row, you go to the next row and another alkali metal.
An AnomalyMost of the alkali metals, such as lithium, sodium, and potassium, are very similar. They are soft, reactive, silvery solids. They have one outer electron and conduct electricity. They are easily cut with a knife. But, there is an exception – an anomaly.
Right at the very top of these, in the same column, and the first element in the Periodic Table is hydrogen! Hydrogen is a gas. It is colorless. It does not conduct electricity (caution: mixed with oxygen, hydrogen can explode from a spark). Hydrogen forms covalent molecules.
Yet…Yet, the Periodic Table suggests hydrogen is a metal. Is it? Does it ever act like a metal?
At Room TemperatureUnder most conditions, hydrogen is not metallic. However, researchers did not fail to consider the possibility it could be under certain conditions. In 1935, it was suggested that extremely high pressure on the order of 250,000 times atmospheric pressure, hydrogen would behave as a metal. Such a pressure may be found deep within the earth. In fact, scientists have looked for the metal there. So far, without success.
What Would Characterize Solid Hydrogen Metal?Ordinarily, hydrogen freezes in the form of diatomic molecules, H2. Solid diatomic hydrogen is an insulator. Under much more severe conditions, the molecules would break apart, not into atoms, but into naked protons and electrons.
The stripped protons would collect into a tight packed matrix or lattice. The distance between them would be less than a Bohr radius (0.0529 x 10⁻9 meters). Although electrons would remain, they would not be identifiable with any particular protons. This is a characteristic of metallic bonding.
Hydrogen Metal LiquidLiquid hydrogen metal would have no rigid matrix. The system of protons and electrons would behave as a fluid.
The May 6, 1998 edition of Cornell News states, “Last year liquid metallic hydrogen was created for less than a microsecond by scientists at Lawrence Livermore National Laboratory in California.”
Such a headline indicates the almost certain existence of a solid form of hydrogen metal. It is expected it will behave as an alkali metal, when formed. In fact, it is postulated to exist in the high pressure centers of huge astronomical objects. It seems hydrogen is right where it belongs in the Periodic Table.
AN EXCITING DEVELOPMENT Followed by a Depressing SetbackIn January 2018 [just 2 years after this article was written] a sample of solid metallic hydrogen was prepared and placed in storage! Yes, it was achieved! Tests were performed. Tests and recently more tests, when, that sample was lost, possibly destroyed. Read about it in these two Science Alert articles, It’s Real: Metallic Hydrogen Has Been Created For The First Time, and The World’s Only Metallic Hydrogen Sample Has Disappeared.
Note: You might also enjoy Why Metals Conduct Electricity
- The Journal of Chemical Physics: On the Possibility of a Metallic Modification of Hydrogen, by E. Wigner, et.al.
- Cornell News: High-pressure scientists ‘journey’ to the center of the Earth, but can’t find elusive metallic hydrogen