Dictionary:
i·on (ī'ŏn', ī'ən)  |
An atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons.
[Greek ion, something that goes, neuter present participle of ienai, to go.]
ion
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| Sci-Tech Encyclopedia: Ion |
An atom or group of atoms that bears an electric charge. Positively charged ions are called cations, and negatively charged ions are called anions. When a single atom gains or loses an electron, monoatomic ions are formed. For example, reaction of the element sodium (Na) with the element chlorine (Cl) leads to the transfer of electrons from Na to Cl to form Na+ cations and Cl− anions. In general, atoms of metallic elements (on the left side of the periodic table) lose electrons to form cations, while atoms of nonmetallic atoms (on the right side of the periodic table) gain electrons to form anions. Ions can bear multiple charges, as in the magnesium ion (Mg2+) or the nitride ion (N3−). The charge on monoatomic ions is usually the same for elements in the same column of the periodic table; for example, hydrogen (H), sodium, lithium (Li), potassium (K), rubidium (Rb), and cesium (Cs) all form +1 ions. See also Periodic table.
Ions can also comprise more than one atom and are then called polyatomic ions. For example, the ammonium ion (NH4+) carries a positive charge and is composed of one nitrogen atom and four hydrogen atoms. The nitrate ion (NO3−) is composed of one nitrogen atom and three oxygen atoms and carries a single negative charge. Polyatomic ions are usually depicted inside brackets with superscripted charges, as shown in the structure below.
Anions and cations can combine to form solid materials called salts, which are named by the cation name followed by the anion name. For a salt composed of the polyatomic ions ammonium and nitrate, the formula is NH4NO3 and the name is ammonium nitrate. For monoatomic ions, the cation name is the same as the element and the anion name is the element name with the ending -ide. Thus, common table salt, NaCl, is called sodium chloride. The ratio of anions to cations must always be such that an electrically neutral material is produced. Thus, magnesium nitrate must contain one magnesium for every two nitrates, giving the formula Mg(NO3)2. See also
| Computer Desktop Encyclopedia: ion |
(1) (IDL On the Net) See IDL.
(2) 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.
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| World of the Body: ions |
Ions carry an electric charge or charges. Those with one or more positive charges are called cations, whereas those with negative charges are called anions. The names arise from considering what happens if a current is passed through an ionic solution; cations migrate to the cathode and anions to the anode, allowing current to flow through the solution. Common inorganic cations found in the body are sodium (Na+), potassium (K+), and calcium (Ca2+), while common anions are chloride (Cl-) and bicarbonate (HCO3-). Neither anions or cations can exist in isolation, as the total electrical charge must be in balance. A solution of sodium chloride will have an equal number of Na+ and Cl- ions, and a solution of calcium chloride will have twice the number of Cl- ions as Ca2+ ions. Organic molecules can also be ionic. The neurotransmitter acetylcholine chloride will give, in solution, a positively charged acetylcholine moiety together with a chloride ion. Some organic molecules may carry a positive and a negative charge on different parts of the molecule and are known as zwitterions.
— Alan W. Cuthbert
See also body fluids; composition of the body.
| Food and Nutrition: ion |
An atom or molecule that has lost or gained one or more electrons, and thus has an electric charge. Positively charged ions are known as cations, because they migrate towards the cathode (negative pole) in solution, while negatively charged ions migrate towards the positive pole (anode) and hence are known as anions.
| Dental Dictionary: ion |
n
An atomic particle, atom, or chemical radical bearing an electrical charge, either negative or positive.
| Geography Dictionary: ion |
An atom or group of atoms that has either lost one or more electrons, making it positively charged (cation), or has gained one or more electrons thereby becoming negatively charged (anion). See ionosphere.
| Britannica Concise Encyclopedia: ion |
For more information on ion, visit Britannica.com.
| Sports Science and Medicine: ion |
An atom or molecule that carries a charge due to the gain or loss of an electron.
| Columbia Encyclopedia: ion |
ion, atom or group of atoms having a net electric charge.
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 ion 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 cation. If an atom or group gains electrons or loses protons, it will have a net negative charge and is called an anion.
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 solution 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 bases; dissociation). Substances that ionize in solution are called electrolytes; 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 radiation. Ultraviolet radiation and low-energy X rays 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 ionosphere). 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 accelerators, 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 chromatography). 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.
| Biology Q&A: What is an ion? |
An ion is an atom that is charged by the loss or gain of
electrons. For example, when an atom gains one or more electrons, it becomes
negatively charged. When an atom loses one or more electrons, it becomes
positively charged.
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| Science Dictionary: ion |
An atom that has either lost or gained one or more electrons, so that it has an electrical charge. Ions can be either positively or negatively charged.
| Veterinary Dictionary: ion |
An atom or group of atoms having a positive (cation) or negative (anion) electric charge by virtue of having gained or lost one or more electrons. Substances forming ions are electrolytes.
- i. channel — see channel.
- dipolar i. — zwitterion.
- hydrogen i. — the positively charged hydrogen atom (H+), present to excess in acid solutions.
- i. pair — the pair of ions created when an atom has had an electron removed by ionizing radiation.
- i. pump — see calcium pump, sodium pump.
- i. trapping — a strategy for treatment of poisonings based on the principle that cell membranes are less permeable to ionized compounds. With knowledge of the characteristics of the toxin, treatment can be given to alter the acid–base balance in favor of ionization.
| Electronics Dictionary: ion |
An atom with fewer electrons in orbit than the number of protons in the nucleus is a positive ion. An atom with a greater number of electrons in orbit than the number of protons in the nucleus is a negative ion.
| Wikipedia: Ion |
For other uses, see Ion (disambiguation).
An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.
Since protons are positively charged and electrons are negatively charged, if there are more electrons than protons, the atom or molecule will be negatively charged. This is called an anion (pronounced /ˈænaɪən/; an-eye-on), from the Greek ἀνά (ana), meaning 'up'.
Conversely, if there are more protons than electrons, the atom or molecule will be positively charged. This is called a cation (pronounced /ˈkætaɪən/; cat-eye-on), from the Greek κατά (kata), meaning 'down'.
An ion consisting of a single atom is called a monatomic ion. If it consists of two or more atoms, it is called a polyatomic ion. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions.
When writing the chemical formula for an ion, its charge is written as a superscript '+' or '−' following a number indicating the difference between the number of protons and the number of electrons. The number is omitted if it is equal to 1. For example, the sodium cation is written as Na+, the '+' indicating that it has one less electron than it has protons. The sulfate anion is written as SO42−, the '2−' indicating that it has two more electrons than it has protons.
If an ion contains unpaired electrons, it is called a radical ion. Just like neutral radicals, radical ions are very reactive.
Contents |
Formation
Formation of monatomic ions
Monatomic ions are formed by the addition of electrons to the valence shell of the atom, or the losing of electrons from this shell. The inner shells of an atom are filled with electrons that are tightly bound to the positively-charged atomic nucleus, and so do not participate in this kind of chemical interaction. The process of gaining or losing electrons from a neutral atom or molecule is called ionization.
Atoms can be ionized by bombardment with radiation, but the more usual process of ionization encountered in chemistry is the transfer of electrons between atoms or molecules. This transfer is usually driven by the attaining of stable ("closed shell") electronic configurations. For example, a sodium atom, Na, has a single electron in its valence shell, surrounding a stable, closed inner shell of 10 electrons. Since the 10-electron configuration is very stable, sodium "likes" to lose its extra electron so that it can attain to this stable configuration, becoming the sodium cation in the process:
- Na → Na+ + e−
On the other hand, a chlorine atom, Cl, has 7 electrons in its valence shell, which is one short of the stable, filled shell with 8 electrons. Thus, chlorine "likes" to gain an extra electron in order to attain to the stable 8-electron configuration, becoming the chloride anion in the process:
- Cl + e− → Cl−
This driving force is what causes sodium and chlorine to undergo a chemical reaction, where the "extra" electron is transferred from sodium to chlorine, forming sodium cations and chloride anions. Being oppositely-charged, these cations and anions combine together to form sodium chloride, NaCl, more commonly known as salt.
Formation of polyatomic and molecular ions
Polyatomic and molecular ions are often formed by the gaining or losing of elemental ions such as H+ in neutral molecules. For example, when ammonia, NH3, accepts a proton, H+, it forms the ammonium ion, NH4+. Ammonia and ammonium have the same number of electrons in essentially the same electronic configuration, but ammonium has an extra proton that gives it a net positive charge.
Ammonia can also lose an electron to gain a positive charge, forming the ion NH3·+. However, this ion is unstable, because it has an incomplete valence shell around the nitrogen atom, making it a very reactive radical ion.
Due to the instability of radical ions, polyatomic and molecular ions are usually formed by gaining or losing elemental ions such as H+, rather than gaining or losing electrons. This allows the molecule to preserve its stable electronic configuration while acquiring an electrical charge.
Ionization potential
The energy required to detach an electron in its lowest energy state from an atom or molecule of a gas with less net electric charge is called the ionization potential, or ionization energy. The nth ionization energy of an atom is the energy required to detach its nth electron after the first n − 1 electrons have already been detached.
Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron, in its outermost shell, so in ionized form it is commonly found with one lost electron, as Na+. On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as Cl−. Caesium has the lowest measured ionization energy of all the elements and helium has the greatest.[1] The ionization energy of metals is generally much lower than the ionization energy of nonmetals, which is why metals will generally lose electrons to form positively-charged ions while nonmetals will generally gain electrons to form negatively-charged ions.
Ionic bonding
Ionic bonding is a kind of chemical bonding that arises from the mutual attraction of oppositely-charged ions. Since ions of like charge repel each other, they do not usually exist on their own. Instead, they are bound to ions of the opposite charge. The resulting compound is called an ionic compound, and is said to be held together by ionic bonding.
The most common type of ionic bonding is seen in compounds of metals and nonmetals (except noble gases, which rarely form chemical compounds). Metals are characterized by having a small number of electrons in excess of a stable, closed-shell electronic configuration. As such, they have the tendency to lose these extra electrons in order to attain to the stable configuration. This property is known as electropositivity. Non-metals, on the other hand, are characterized by having an electron configuration just a few electrons short of a stable configuration. As such, they have the tendency to gain more electrons in order to attain to the stable configuration. This tendency is known as electronegativity. When a highly electropositive metal is combined with a highly electronegative nonmetal, the extra electrons from the metal atoms are transferred to the electron-deficient nonmetal atoms. This reaction produces metal cations and nonmetal anions, which are attracted to each other to form a salt.
Plasma
A collection of non-aqueous gas-like ions, or even a gas containing a proportion of charged particles, is called a plasma, often called the fourth state of matter because its properties are quite different from solids, liquids, and gases. Astrophysical plasmas containing predominantly a mixture of electrons and protons, may make up as much as 99.9% of visible matter in the universe.[2]
Applications
Ions are essential to life. Sodium, potassium, calcium and other ions play an important role in the cells of living organisms, particularly in cell membranes. They have many practical, everyday applications in items such as smoke detectors, and are also finding use in unconventional technologies such as ion engines. Inorganic dissolved ions are a component of total dissolved solids, an indicator of water quality in the world.
Common ions
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See also
References
 |
This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2007) |
- ^ http://www.lenntech.com/Periodic-chart-elements/ionization-energy.htm Chemical elements listed by ionization energy
- ^ Plasma, Plasma, Everywere Science@NASA Headline news, Space Science n° 158, September 7, 1999.
External links
- Department of Education, Newfoundland and Labrador-Canada "Periodic Chart of IonsPDF (70.9 KiB)". A Periodic table reporting ionic charges for every chemical element.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
| Translations: Ion |
Ελληνική (Greek)
n. - (φυσ.) ιόν
Português (Portuguese)
n. - íon (m) (Quím.) (Fís.)
中文（简体）(Chinese (Simplified))
离子
中文（繁體）(Chinese (Traditional))
n. - 離子
العربيه (Arabic)
(الاسم) الأيون
עברית (Hebrew)
n. - יון (אטום טעון חשמל)
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Related answers
- Why is an iron ion is attracted to a sulfide ion but not to a zinc ion?
- Why an iron ion is attracted to a sulfide ion but not to a zinc ion?
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