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In mathematics, more precisely in measure theory, an atom is a measurable set that has positive measure and contains no set of smaller positive measures. A measure that has no atoms is called non-atomic or atomless .
An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper.
An example of a non-similar one is the non-bonding orbital of the allyl anion, whose electron density is concentrated on the first and third carbon atoms. [1] In fully delocalized canonical molecular orbital theory, it is often the case that none of the molecular orbitals of a molecule are strictly non-bonding in nature.
A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example, carbon-13 with 6 protons and 7 neutrons. The nuclide concept (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, whereas the isotope concept (grouping all atoms of each element) emphasizes chemical over nuclear.
A non-fullerene example is [As@Ni 12 As 20] 3−, an ion in which one arsenic (As) atom is trapped in a cage formed by the other 32 atoms. This notation was proposed in 1991 [ 3 ] with the discovery of fullerene cages ( endohedral fullerenes ), which can trap atoms such as La to form, for example, La@C 60 or La@C 82 .
Those that may in the future be found to be radioactive are expected to have half-lives longer than 10 22 years (for example, xenon-134). [citation needed] In April 2019 it was announced that the half-life of xenon-124 had been measured to 1.8 × 10 22 years.
Examples are the transition metals where the non-bonding pairs do not influence molecular geometry and are said to be stereochemically inactive. In molecular orbital theory (fully delocalized canonical orbitals or localized in some form), the concept of a lone pair is less distinct, as the correspondence between an orbital and components of a ...
Non-stoichiometric compounds also exhibit special electrical or chemical properties because of the defects; for example, when atoms are missing, electrons can move through the solid more rapidly. [ not verified in body ] Non-stoichiometric compounds have applications in ceramic and superconductive material and in electrochemical (i.e., battery ...