Energy & Green Tech

Hydrogen: Handle with care

When produced and used properly, hydrogen can potentially play many roles in the transition toward clean energy and industrial systems. Hydrogen can directly replace natural gas and coal in industrial and manufacturing processes ...

Electronics & Semiconductors

Bulky additives could make cheaper solar cells last longer

An insight into preventing perovskite semiconductors from degrading quickly, discovered at the University of Michigan, could help enable solar cells estimated to be two to four times cheaper than today's thin-film solar panels.

Energy & Green Tech

A new system for producing green hydrogen cheaply and efficiently

What does it take to produce green hydrogen more efficiently and cheaply? Apparently, small ruthenium particles and a solar-powered system for water electrolysis. This is the solution proposed by a joint team involving the ...

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A molecule is defined as a sufficiently stable, electrically neutral group of at least two atoms in a definite arrangement held together by very strong (covalent) chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules and biomolecules.

In the kinetic theory of gases the term molecule is often used for any gaseous particle regardless of its composition. According to this definition noble gas atoms are considered molecules despite the fact that they are composed of a single non-bonded atom.

A molecule may consist of atoms of a single chemical element, as with oxygen (O2), or of different elements, as with water (H2O). Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules.

No typical molecule can be defined for ionic crystals (salts) and covalent crystals (network solids), although these are often composed of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond or sodium chloride). The theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding. In glasses (solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds without any definable molecule, but also without any of the regularity of repeating units that characterises crystals.

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