With a whiff, 'e-nose' can sense fine whiskey

Scotch or Irish, single malt or blended? While a whiskey enthusiast might be able to distinguish the good stuff from run-of-the-mill by smell alone, most tipplers rely on the label, black or otherwise.


Affordable and productive electrolysis from a 3D printer

Stephane Weusten defended his Ph.D. on how to build an inexpensive and effective electrolyzer using a 3D printer. He easily adjusted geometrical parameters to improve the performance of the device. This accelerates research ...

Energy & Green Tech

New flow battery stores power in simple organic compound

The intermittent supply of green electricity requires large-scale storage to keep our power grids stable. Since normal batteries do not scale very well, the idea of using flow batteries, which store electricity in a fluid ...

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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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