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What Are the Different States of Hydrogen?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

The importance of hydrogen for our lives is something we don’t think about but can easily accept. You drink it when it’s bonded to oxygen, otherwise known as water. It’s the first fuel source for a star as it radiates heat, allowing life as we know it to exist. And it was one of the first molecules to form in the Universe. But maybe you are not familiar with the different states of hydrogen. Yes, it’s related to the state of the matter, like a solid/liquid/gas, but more elusive classifications that one may not be familiar with but are just as important will be key here.

Molecular Form

Hydrogen in this state is in a gaseous phase and rather interestingly is a dual-atomic structure. That is, we represent it as H­2, with two protons and two electrons. No neutrons seems odd, right? It should be, because hydrogen is rather unique with this regard in that its atomic format doesn’t have a neutron. This does give it some fascinating properties such as a fuel source and its ability to bond to many different elements, the most relevant to us being water (Smith).

Metallic Form

Unlike our gaseous molecular hydrogen, this form of hydrogen is pressurized to the point that it becomes a liquid with special electrical conductive properties. That’s why it’s called metallic – not because of a literal comparison but because of the ease that electrons move about. Stewart McWilliams (University of Edinburgh) and a joint-U.S./China team looked into the properties of metallic hydrogen by using lasers and diamonds. Hydrogen is placed between two layers of diamonds in close proximity to each other. By vaporizing the diamond, sufficient pressure is generated up to 1.5 million atms and temperatures reach 5,500 degrees Celsius. By observing the light absorbed and emitted during this, properties of the metallic hydrogen could be discerned. It is reflective like metals are and is “15 times denser than hydrogen chilled to 15K” which was the temperature of the initial sample (Smith, Timmer, Varma).

While metallic hydrogen’s format makes it an ideal energy device for sending or storing, it’s difficult to make because of those pressure and temperature requirements. Scientists wonder if perhaps adding some impurities to molecular hydrogen could make the transition to metallic easier to coerce, for if the bonding between the hydrogens is altered then the physical conditions required to change into metallic hydrogen should be altered also, perhaps for the better. Ho-kwang Mao and team attempted this by introducing argon (a noble gas) to molecular hydrogen to create a weakly bounded (but under extreme pressure at 3.5 million atms) compound. When they examined the material in the diamond configuration from before, Mao was surprised to find that the argon actually made it harder for the transition to occur. The argon pushed the bonds further apart, reducing the interplay required for metallic hydrogen to form (Ji).

Ho-kwang Mao's set-up for metallic hydrogen production.

Ho-kwang Mao's set-up for metallic hydrogen production.

Clearly, mysteries still exist. One that scientists did narrow down was the magnetic properties of metallic hydrogen. A study by Mohamed Zaghoo (LLE) and Gilbert Collins (Rochester) looked at the conductivity of metallic hydrogen to see its conductive properties in relation to the dynamo-effect, the way our planet generates magnetic field by the movement of material. The team didn’t use diamonds but instead the OMEGA laser to strike a hydrogen capsule at high pressure as well as temperature. They were then able to see the minute movement of their material and capture magnetic data. This is insightful, for the conditions required to make metallic hydrogen are best found in the Jovian planets. Huge reservoirs of hydrogen are under sufficient pressure and heat to create the special material. With this large amount of it and the constant churning of it, a massive dynamo-effect is developed and so with this data scientists can build better models of these planets (Valich).

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Dark Form

With this format, hydrogen doesn’t display metallic nor gaseous properties. Instead, this is something in the middle of them. Dark hydrogen doesn’t send out light nor does it reflect it (hence the dark) like molecular hydrogen, but instead sheds thermal energy like metallic hydrogen does. Scientists first got the clues for this via the Jovian planets (again), when models were unable to account for the excessive heat they were shedding. Models showed molecular hydrogen on the exterior layers with metallic below it. Within these layers, pressures should be sufficiently high to produce dark hydrogen and make the heat needed to match observations while remaining invisible to sensors. As for seeing it on Earth, remember that study by McWilliams? Turns out, when they were around 2,400 degrees Celsius and around 1.6 million atm, they noticed their hydrogen began displaying properties of both metallic and molecular hydrogen – a semi-metallic state. Where else this form is as well as its applications are still unknown at this time (Smith).

So remember, every time you take a sip of water or breath in, a little bit of hydrogen enters you. Think about its different formats and how miraculous it is. And there are so many more elements out there too…

Works Cited

Ji, Cheng. “Argon is not the ‘dope’ for metallic hydrogen.” innovations-report, 24 Mar. 2017. Web. 28 Feb. 2019.

Smith, Belinda. “Scientists discover new ‘dark’ state of hydrogen.” Cosmos. Web. 19 Feb. 2019.

Timmer, John. “80 Years late, scientists finally turn hydrogen into a metal.” Conte Nast., 26 Jan. 2017. Web. 19 Feb. 2019.

Valich, Lindsey. “Researchers unravel more mysteries of metallic hydrogen.” innovations-report, 24 Jul. 2018. Web. 28 Feb. 2019.

Varma, Vishnu. “Physicists make metallic hydrogen in the lab for the first time.” Cosmos. Web. 21 Feb. 2019.

© 2020 Leonard Kelley

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