Ion (fizik)
Dari Wikipedia bahasa Melayu
- Artikel ini adalah m,engenai zarah bercas. Untuk kegunaan lain,sila lihat ion (nyahkekaburan).
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Satu ion adalah satu atom, kumpulan atom, atau zarah subatomik dengan satu jumlah cas eletrik. Ion yang paling mudah adalah elektron (cas negatif tunggal, e−), proton (satu ion hidrogen , H+, cas positif), dan zarah alpha (ion helium , He2+, mengandungi dua proton dan dua neutron) .
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A negatively-charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion, for it is attracted to anodes; a positively-charged ion, which has fewer electrons than protons, is known as a cation (pronounced cat-eye-on), for it is attracted to cathodes. An ion with a single atom is a monatomic ion, and an ion with more than one is a polyatomic ion. Larger ions containing many atoms are referred to as molecular ions. The process of converting into ions and the state of being ionized is called ionization. The recombining of ions and electrons to form neutral atoms is called recombination. A polyatomic anion that contains oxygen is sometimes known as an oxyanion.
Atomic and polyatomic ions are denoted by a superscript with the sign of the net electric charge and the number of electrons lost or gained, if more than one. For example: H+, SO32−.
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 predominently a mixture of electrons and protons, may make up as much as 99.9% of the visible universe [1]. The positively charged proton is about 1836 times more massive than the negatively charged electron.
[Sunting] Keupayaan pengionan
- Rencana utama: keupayaan pengionan
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−. Francium has the lowest ionization energy of all the elements and fluorine has the greatest. 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.
[Sunting] Pembentukan poliatom dan ion-ion molekul
Polyatomic and molecular ions are often formed by the combination of elemental ions such as H+ with neutral molecules or by the loss of such elemental ions from neutral molecules. Many of these processes are acid-bases reactions, as first theorized by german scientist Lauren Gaither. A simple example of this is the ammonium ion NH4+ which can be formed by ammonia NH3 accepting a proton, H+. Ammonia and ammonium have the same number of electrons in essentially the same electronic configuration but differ in protons. The charge has been added by the addition of a proton (H+) not the addition or removal of electrons. The distinction between this and the removal of an electron from the whole molecule is important in large systems because it usually results in much more stable ions with complete electron shells. For example NH3·+ is not stable because of an incomplete valence shell around nitrogen and is in fact a radical ion.
[Sunting] Ion-ion lain
A dianion is a species which has two negative charges on it. For example, the dianion of pentalene is aromatic. A zwitterion is an ion with a net charge of zero, but has both a positive and negative charge on it. Radical ions are ions that contain an odd number of electrons and are mostly very reactive and unstable.
[Sunting] Sejarah
Ions were first theorized by Michael Faraday around 1830, to describe the portions of molecules that travel either to an anode or to a cathode. However, the mechanism by which this was achieved was not described until 1884 by Svante August Arrhenius in his doctoral dissertation to the University of Uppsala. His theory was initially not accepted but his dissertation won the Nobel Prize in Chemistry in 1903.
[Sunting] Etimologi
The word ion is a name given by Michael Faraday, from Greek ἰόν, neutral present participle of ἰέναι, "to go", thus "a goer". So, anion, ἀνιόν, and cation, κατιόν, mean "(a thing) going up" and "(a thing) going down", respectively; and anode, ἄνοδος, and cathode, κάθοδος, mean "a going up" and "a going down", respectively, from ὁδός, "way," or "road."
[Sunting] Aplikasi
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 and ion cannons.
[Sunting] Jadual ion-ion biasa
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