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Hydrogen Bonds

Hydrogen Bonds

A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...

Hydrogen Bonds

Hydrogen Bonds

Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
Hydrogen Bonds Control the World!
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared.

Phase Diagram

Phase Diagram

The phase of a given substance depends on the pressure and temperature. Thus, plots of pressure versus temperature showing the phase in each region provide considerable insights into the thermal properties of substances. Such plots are known as phase diagrams. For instance, in the phase diagram for water (Figure 1), the solid curve boundaries between the phases indicate phase transitions (i.e., temperatures and pressures at which the phases coexist).

Phase Diagram

Phase Diagram

A phase diagram is a graphical representation of the physical states of a substance under different conditions of temperature and pressure. It shows the boundaries between solid, liquid, and gas phases and the conditions at which these phases coexist in equilibrium. An area in a phase diagram represents a single phase, whereas lines or phase boundaries represent the equilibrium between two phases.In the phase diagram of water, the boundary line between the solid and liquid states illustrates...

Phase Diagrams

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. These diagrams indicate the physical states that exist under specific conditions of pressure and temperature and also provide the pressure dependence of the phase-transition temperatures (melting points, sublimation points, boiling points). Regions or areas labeled solid, liquid, and gas represent single phases, while lines or curves represent...

States of Water

States of Water

Water exists in any one of the three classical states: solid (ice), liquid (water), and gas (steam or water vapor). The state of water depends on i) the intermolecular forces that draw molecules together and ii) the kinetic energy that leads to movements that pull them apart.
Water freezes when the intermolecular forces are greater than the kinetic energy. Unlike most other substances, water is less dense in its solid state than in its liquid state. This is because each water molecule can form...

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Related Experiment Video

Updated: May 19, 2026

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

Published on: March 31, 2018

Room-temperature structures of solid hydrogen at high pressures.

Hanyu Liu¹, Li Zhu, Wenwen Cui

¹State Key Lab of Superhard Materials, Jilin University, Changchun 130012, China.

The Journal of Chemical Physics

|August 28, 2012

Summary

This summary is machine-generated.

High-pressure solid hydrogen transitions into insulating and metallic phases at 300 K. Simulations reveal a partially ordered hexagonal close-packed (po-hcp) phase and a metallic Cmca phase, supporting metallization below 300 GPa.

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Area of Science:

Condensed Matter Physics
Materials Science
Computational Chemistry

Background:

Solid hydrogen exhibits complex phase transitions under extreme pressures.
Understanding these phases is crucial for high-pressure physics and planetary science.

Purpose of the Study:

To explore the structural and electronic properties of solid hydrogen at 300 K between 150-300 GPa.
To investigate phase transitions and their stability.
To provide theoretical support for experimental observations of hydrogen metallization.

Main Methods:

First-principles metadynamics simulations.
Gibbs free energy calculations.
Analysis of structural and bonding characteristics.

Main Results:

At 200 GPa, a transition from hexagonal close-packed (hcp) to a partially ordered hcp (po-hcp) phase was observed.
The po-hcp phase features graphene-like layers and disordered molecules, explaining high Raman peaks (>4000 cm(-1)).
At 275 GPa, a transformation to the metallic Cmca phase was predicted, stable at lower pressures than previously thought.

Conclusions:

The study confirms the stability of the po-hcp and metallic Cmca phases at 300 K.
Temperature plays a significant role in stabilizing these phases.
Theoretical results support the claim of solid hydrogen metallization below 300 GPa at 300 K.