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see CreusaCreusa
, in Greek mythology. 1 Daughter of Erechtheus and wife of Xuthus. Her sons, Achaeus by Xuthus, and Ion by Xuthus or Apollo, are the ancestors of the Achaeans and the Ionians. 2 Princess of Corinth: see Jason and Medea.
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atom or group of atoms having a net electric chargecharge,
property of matter that gives rise to all electrical phenomena (see electricity). The basic unit of charge, usually denoted by e, is that on the proton or the electron; that on the proton is designated as positive (+e
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Positive and Negative Electric Charges

A neutral atom or group of atoms becomes an ion by gaining or losing one or more electrons or protons. Since the electron and proton have equal but opposite unit charges, the charge of an ion is always expressed as a whole number of unit charges and is either positive or negative. A simple ion consists of only one charged atom; a complex ioncomplex ion,
charged molecular aggregate (see ion), consisting of a metallic atom or ion to which is attached one or more electron-donating molecules. In some complex ions, such as sulfate, SO4−2
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 consists of an aggregate of atoms with a net charge. If an atom or group loses electrons or gains protons, it will have a net positive charge and is called a cationcation
, atom or group of atoms carrying a positive charge. The charge results because there are more protons than electrons in the cation. Cations can be formed from a metal by oxidation (see oxidation and reduction), from a neutral base (see acids and bases) by protonation, or
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. If an atom or group gains electrons or loses protons, it will have a net negative charge and is called an anionanion
, atom or group of atoms carrying a negative charge. The charge results because there are more electrons than protons in the anion. Anions can be formed from nonmetals by reduction (see oxidation and reduction) or from neutral acids (see acids and bases) or polar compounds
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Since ordinary matter is electrically neutral, ions normally exist as groups of cations and anions such that the sum total of positive and negative charges is zero. In common table salt, or sodium chloride, NaCl, the sodium cations, Na+, are neutralized by chlorine anions, Cl. In the salt sodium carbonate, Na2CO3, two sodium cations are needed to neutralize each carbonate anion, CO3−2, because its charge is twice that of the sodium ion.

Ionization of Neutral Atoms

Ionization of neutral atoms can occur in several different ways. Compounds such as salts dissociate in solutionsolution,
in chemistry, homogeneous mixture of two or more substances. The dissolving medium is called the solvent, and the dissolved material is called the solute. A solution is distinct from a colloid or a suspension.
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 into their ions, e.g., in solution sodium chloride exists as free Na+ and Cl ions. Compounds that contain dissociable protons, or hydrogen ions, H+, or basic ions such as hydroxide ion, OH, make acidic or basic solutions when they dissociate in water (see acids and basesacids and bases,
two related classes of chemicals; the members of each class have a number of common properties when dissolved in a solvent, usually water. Properties
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; dissociationdissociation,
in chemistry, separation of a substance into atoms or ions. Thermal dissociation occurs at high temperatures. For example, hydrogen molecules (H2
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). Substances that ionize in solution are called electrolyteselectrolyte
, electrical conductor in which current is carried by ions rather than by free electrons (as in a metal). Electrolytes include water solutions of acids, bases, or salts; certain pure liquids; and molten salts.
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; those that do not ionize, like sugar and alcohol, are called nonelectrolytes. Ions in solution conduct electricity. If a positive electrode, or anode, and a negative electrode, or cathode, are inserted into such a solution, the ions are attracted to the electrode of opposite charge, and simultaneous currents of ions arise in opposite directions to one another. Nonelectrolytes do not conduct electricity.

Ionization can also be caused by the bombardment of matter with high-speed particles or other radiationradiation
, term applied to the emission and transmission of energy through space or through a material medium and also to the radiated energy itself. In its widest sense the term includes electromagnetic, acoustic, and particle radiation, and all forms of ionizing radiation.
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. Ultraviolet radiationultraviolet radiation,
invisible electromagnetic radiation between visible violet light and X rays; it ranges in wavelength from about 400 to 4 nanometers and in frequency from about 1015 to 1017 hertz.
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 and low-energy X raysX ray,
invisible, highly penetrating electromagnetic radiation of much shorter wavelength (higher frequency) than visible light. The wavelength range for X rays is from about 10−8 m to about 10−11
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 excite molecules in the upper atmosphere sufficiently to cause them to lose electrons and become ionized, giving rise to several different layers of ions in the earth's atmosphere (see ionosphereionosphere
, series of concentric ionized layers forming part of the upper atmosphere of the earth from around 30 to 50 mi (50 to 80 km) to 250 to 370 mi (400 to 600 km) where it merges with the magnetosphere, the region of the Van Allen radiation belts.
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). A gas can be ionized by passing an electron current through it; the ionized gas then permits the passage of a much higher current. Heating to high temperatures also ionizes substances; certain salts yield ions in their melts as they do in solution.

Applications of Ionization

Ionization has many applications. Vapor lamps and fluorescent lamps take advantage of the light given off when positive ions recombine with electrons. Because of their electric charge the movement of ions can be controlled by electrostatic and magnetic fields. Particle acceleratorsparticle accelerator,
apparatus used in nuclear physics to produce beams of energetic charged particles and to direct them against various targets. Such machines, popularly called atom smashers, are needed to observe objects as small as the atomic nucleus in studies of its
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, or atom smashers, use both fields to accelerate and aim electrons and hydrogen and helium ions. The mass spectrometer utilizes ionization to determine molecular weights and structures. High-energy electrons are used to ionize a molecule and break it up into fragment ions. The ratio of mass to charge for each fragment is determined by its behavior in electric and magnetic fields. The ratio of mass to charge of the parent ion gives the molecular weight directly, and the fragmentation pattern gives clues to the molecular structures.

In ion-exchange reactions a specially prepared insoluble resin with attached dissociable ions is packed into a column. When a solution is passed through the column, ions from the solution are exchanged with ions on the resin (see chromatographychromatography
, resolution of a chemical mixture into its component compounds by passing it through a system that retards each compound to a varying degree; a system capable of accomplishing this is called a chromatograph.
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). Water softeners use the mineral zeolite, a natural ion-exchange resin; sodium ions from the zeolite are exchanged for metal ions from the insoluble salt that makes the water hard, converting it to a soluble salt. Ion-permeable membranes allow some ions to pass through more readily than others; some membranes of the human nervous system are selectively permeable to the ions sodium and potassium.

Engineers have developed experimental ion propulsion engines that propel rockets by ejecting high-speed ions; most other rocket engines eject combustion products. Although an ion engine does not develop enough thrust to launch a rocket into earth orbit, it is considered practical for propelling one through interplanetary space on long-distance trips, e.g., between the earth and Jupiter. If left running for long periods of time on such a trip, the ion engine would gradually accelerate the rocket to immense speeds.


(ÿ -on, -ŏn) An atom or molecule that has lost or gained one or more electrons, thus having a positive or negative charge.


An isolated electron or positron or an atom or molecule which by loss or gain of one or more electrons has acquired a net electric charge.


an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons


(1) (IDL On the Net) See IDL.

(2) (ION) An NVIDIA graphics platform typically used in Atom-based netbooks. See Intel Atom.

(3) An atom with fewer or greater electrons than normal as a result of a chemical reaction in the material. A positive ion, called a "cation" (pronounced "cat-eye-en"), is an atom that has one or more electrons stripped out, which means it has fewer electrons in its electron shells than it has protons in its nucleus. A negative ion, called an "anion" (pronounced "an-eye-en") is an atom that has one or more electrons forcibly added.

Batteries Contain Positive and Negative Ions
In a battery, there are positive ions on one side and negative ions on the other. When a conductor is placed in between to complete the circuit, the electrons flow from the negative ions to the positive side where they join the positive ions. See ion deposition.
References in periodicals archive ?
Non-selectivity of chloride ion-selective electrode used in the Hitachi 705.
Comparison of three commercially available ion-selective electrodes for ionized magnesium determination in serum: a two-center study [Abstract].
Ion-selective electrodes (ISEs) have become the predominant methodology for measuring serum lithium [1].
31P]-NMR spectroscopy, and a unique magnesium ion-selective electrode [Review].
Pseudohyponatremia is said to be less likely encountered with ion-selective electrode methods, without distinction made between diluted and nondiluted ISE methodology.
27, 2014 /PRNewswire/ -- This report analyzes the worldwide markets for Electrodes for Medical Devices in US$ Thousand by the following Product Segments: Blood Gas Electrodes, Defibrillator Electrodes, ECG Electrodes, EEG/EMG/ENG Electrodes, Electrosurgical Electrodes, Ion-selective Electrodes, pH Electrodes, Pacemaker Electrodes, and TENS Electrodes.
Fluoride ion-selective electrodes respond to the fluoride concentration in a non-linear relationship following the Nernst Equation [18].
It is gratifying that there is to be a link between the Hankow Union Hospital in Hunan Province and the College of Medicine of Swansea University, especially as it is now nearly 30 years since I gave a course of lectures on electrochemistry and ion-selective electrodes (with roles in blood electrolyte analysis) to an audience of several hundred at Hunan University in Changsha in October 1983.
This unit utilizes a unique soil sampling device and ion-selective electrodes to capture pH readings at a sampling density of 5-10 samples per 0.
The blood gas chapter seems up-to-date with respect to its inclusion of very contemporary devices such as ion-selective electrodes and indwelling fiberoptic catheters.