Electronics & Semiconductors

A molecular shift register that can be controlled by external charges

In recent years, electronics engineers have been trying to create molecular-scale electronics, new types of devices that use single molecules. In order for these devices to work, however, scientists first need to identify ...

Electronics & Semiconductors

A new type of hybrid colloidal quantum dot/organic solar cells

Solution-processed semiconductors, including materials such as perovskites and quantum dots (i.e., small particles of matter in the quantum size regime), are substances with a conductivity ranging between that of insulators ...

Energy & Green Tech

New organic flow battery brings decomposing molecules back to life

After years of making progress on an organic aqueous flow battery, Harvard University researchers ran into a problem: the organic anthraquinone molecules that powered their ground-breaking battery were slowly decomposing ...

Computer Sciences

Computer scientists create programmable self-assembling DNA

Computer scientists at University of California, Davis, Maynooth University in Ireland and the California Institute of Technology have created DNA molecules that can self-assemble into patterns essentially by running their ...

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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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