ion, ion- +
(Greek: ion, "going"; neuter present participle of ienai, "to go"; because an ion moves toward the electrode of an opposite charge)
2. The charging of neutral particles in the atmosphere through violent contact with charged particles.
3. The production of ions in the atmosphere by the loss of an electron from a molecule, typically, for example, by cosmic rays or cosmic radiation.
Cosmic rays and radioactive decay are the main sources of atmospheric ionization.
Radioactivity at the surface can also produce ions in the lowest layer of the atmosphere.
Given an adequate mean free path, a primary ion caused by the incident radiation can be accelerated by the applied voltage to the point where its collisions produce several other ions, where each secondary ion does the same thing, and so on, causing an "avalanche".
The multiplication of ions can be in the millions or more.
Certain carbonium ions can be prepared in such a way that they are stable enough for study; more frequently they are only short-lived forms (intermediates) occurring during chemical reactions.
Carbonium ions are, in fact, one of the most common classes of intermediates in organic reactions, and knowledge of the structures and properties of these substances is fundamental to understanding reactions in which they occur.
Many of these reactions are of synthetic, biochemical, or industrial importance.
Special types of accelerators are capable of producing fairly intense, high-energy beams of heavy ions, which are used in basic research, as in the production of synthetic transuranium elements (for example, hahnium [atomic number 105]).
The hydrogen nucleus is made up of a particle carrying a unit positive electric charge, called a proton.
Because the bare nucleus can readily combine with other particles (electrons, atoms, and molecules), the isolated hydrogen ion can exist only in a nearly particle-free space (high vacuum) and in the gaseous state.
In common usage, the term hydrogen ion is used to refer to the hydrogen ion present in water solutions, in which it exists as the combined molecule H + H2O.
The amount of hydrogen ion present in a water solution is used as a measure of the acidity of a substance; the higher the concentration of hydrogen ion the more acidic the solution and the lower the pH.
In electrolysis, positive ions (cations) travel to the cathode, while negative ions (anions) travel to the anode.2. An atom from which one or more electrons have been torn off, leaving a positively charged particle.
Negative ions are atoms which have acquired one or more extra electrons, and clusters of atoms can also become ions.3. Etymology: from 1834, introduced by English physicist and chemist Michael Faraday, coined from Greek ion, neuter, present participle of ienai, "to go".
2. A linear accelerator in which ions are accelerated by an electric field in a standing-wave pattern that is set up in a resonant cavity by external oscillators or amplifiers.
2. The scattering in a nearly backward direction of an ion beam incident on a film or body.
2. A trans-membrane pore that presents a hydrophilic (dissolve in or mix with water) channel for ions to cross a lipid bilayer (layer two molecules thick) down their electrochemical gradients.
3. Protein expressed by virtually all living cells that creates a pathway for charged ions from dissolved salts, including sodium, potassium, calcium, and chloride ions, to pass through the otherwise impermeant lipid cell membrane.
Operation of cells in the nervous system, contraction of the heart and of skeletal muscle, and secretion in the pancreas are examples of physiological processes that require ion channels. In addition, ion channels in the membranes of intracellular organelles are important for regulating cytoplasmic calcium concentration and acidification of specific subcellular compartments
Ongoing basic research on ion channels seeks to understand the structural basis for permeability, ion selectivity, and gating at the molecular level.
Research efforts also attempt to answer questions about the cellular regulation of ion channel protein synthesis and about the subcellular distribution and ultimate degradation of channels.
In addition, compounds with greater specificity and potency for channels involved in pain sensation, cardiovascular disease, and other pathological conditions are potential sources for drug development.