Difference Between Molecular and Metallic Hydrogen

The key difference between molecular and metallic hydrogen is that molecular hydrogen has gaseous properties, whereas metallic hydrogen has metallic properties similar to that of alkali metals.

Hydrogen is the first chemical element in the periodic table of elements. It usually occurs in the gaseous state as dihydrogen molecule. In this state, hydrogen is named as molecular hydrogen because it is in the molecular form. In addition to the gaseous state, hydrogen can occur in the liquid state, solid state, slush state, and in the metallic state.

CONTENTS

1. Overview and Key Difference
2. What is Molecular Hydrogen
3. What is Metallic Hydrogen
4. Side by Side Comparison – Molecular vs Metallic Hydrogen in Tabular Form
5. Summary

What is Molecular Hydrogen?

The term molecular hydrogen refers to the dihydrogen gas state. It is the naturally occurring state of hydrogen. The chemical formula of molecular hydrogen is H₂ and has two hydrogen atoms bonded to a single covalent bond between them. The molecular weight of this chemical species is 2.01 g/mol.

When considering the properties of molecular hydrogen, it is colourless, odourless, tasteless, non-toxic and highly combustible. Also, it is a nonmetallic form of hydrogen. In addition, hydrogen gas readily forms covalent bonds with other nonmetallic chemical elements, and they can also react with metallic elements. Therefore, hydrogen in any molecule can be named as molecular hydrogen.

Hydrogen gas naturally occurs in our atmosphere (mainly in the upper atmosphere) but in very trace amounts. However, we can produce hydrogen gas artificially via the reaction between acids and metals which evolves hydrogen gas as a byproduct. However, in the industrial scale productions, hydrogen gas is mainly produced from natural gas. Less often, it is also produced from electrolysis of water.

Hydrogen gas is highly flammable. It can react with oxygen gas, producing water and heat. Pure oxygen-hydrogen flame radiates UV light. Moreover, hydrogen gas can react with almost all oxidizing materials. For example, it can react with chlorine gas spontaneously and violently at room temperature, forming hydrogen chloride.

What is Metallic Hydrogen?

Metallic hydrogen is a phase of hydrogen which has properties of a typical metal. Therefore, this type of hydrogen can act as an electrical conductor. The concept about metallic hydrogen first came into the stage in 1935 after Eugene Wigner and Hillard Bell Huntington who predicted the concept of metallic hydrogen on a theoretical background.

When considering the properties of metallic hydrogen, it can exist as a liquid at high pressure and temperature conditions. Here, the pressure has to be more than 25 Gpa, where there is a bulk phase containing a lattice of protons and delocalized electrons. According to the assumptions of researchers, metallic hydrogen occurs in the interior of planets such as Jupiter and Saturn. Moreover, liquid metallic hydrogen is also a possible state according to the theories. Apart from that, it is assumed that metallic hydrogen has superconductivity properties.

What is the Difference Between Molecular and Metallic Hydrogen?

The key difference between molecular and metallic hydrogen is that molecular hydrogen has gaseous properties, whereas metallic hydrogen has metallic properties similar to that of alkali metals. Moreover, molecular hydrogen is made up of dihydrogen molecules while metallic hydrogen is made up of proton lattice and delocalized electrons.

Furthermore, another difference between molecular and metallic hydrogen is that molecular hydrogen occurs in the gaseous state while metallic hydrogen occurs in the metallic state.

Summary – Molecular vs Metallic Hydrogen

Molecular hydrogen usually occurs in the gaseous state. Other than the gaseous state, hydrogen can occur in the liquid state, solid-state, slush state, and in the metallic state. The key difference between molecular and metallic hydrogen is that molecular hydrogen has gaseous properties, whereas metallic hydrogen has metallic properties similar to that of alkali metals.

Reference:

1. “24.2H: Dihydrogen.” Chemistry LibreTexts, Libretexts, 5 June 2019, Available here.
2. “Hydrogen.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.

Image Courtesy:

1. “Oxidation of hydrogen gas” By Bensaccount (talk) (Uploads) – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Jupiter diagram” By Kelvinsong – Own work (CC BY-SA 3.0) via Commons Wikimedia