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Ion

Ion

: This article is about the electrically charged particle. For other uses of this word, see ion (disambiguation). An ion is an atom or group of atoms with a net electric charge. A negatively charged ion, which has more electrons in its electron shell than it has protons in its nucleus, is known as an anion, for it is attracted to anodes, and 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. 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. Polyatomic anions which contain oxygen are sometimes known as 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⁺, S O₃²⁻. A collection of non-aqueous ions, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its properties are quite different from solids, liquids, and gases.

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⁻. Francium has the lowest ionization energy of all the elements and fluorine has the greatest.

Other ions

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.

History

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.

Etymology

The word ion is a name given by Michael Faraday, from Greek , neutral present participle of , "to go", thus "a goer". So, anion, , and cation, κ, mean "(a thing) going up" and "(a thing) going down", respectively, and anode, , and cathode, κ, mean "a going up" and "a going down", respectively, from , "way".

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 and ion cannons. Category:Physical chemistry ko:이온 ms:Ion ja:イオン simple:Ion th:ไอออน

Ion (disambiguation)

- In physics, an ion is an atom or group of atoms with a net electric charge, having lost (cation) or gained (anion) an electron.
- In computing, Ion is a window manager for the X Window System.
- In ancient Greece, Ion of Chios was a writer and philosopher.
- In ancient Greek philosophy, Ion is a dialogue by Plato, between Socrates and Ion, a reciter of epic poems.
- In ancient Greek theatre, Ion is a play by Euripedes on the relationship between humans and the gods, in which Ion is instead the son of Apollo.
- The Saturn ION is a compact car sold by General Motors.
- In ancient Greek mythology, Ionas, also called Ion, was the son of Xuthus and Creüsa, daughter of Erechtheus.

Atom

:For alternative meanings see atom (disambiguation). An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. It is the smallest unit of an element to retain all the chemical properties of that element. The word atom originally meant a smallest possible particle of matter, not further divisible. Later, the objects that had been called atoms were found to be further divisible into smaller subatomic particles, but the word atom nonetheless continues to refer to them. Most atoms are composed of three types of massive subatomic particles which govern their external properties:
- electrons, which have a negative charge and are the least massive of the three;
- protons, which have a positive charge and are about 1836 times more massive than electrons; and
- neutrons, which have no charge and are about 1838 times more massive than electrons. Together, protons and neutrons form the nucleus of an atom, which is surrounded by the electrons. Atoms can differ in the number of each of the subatomic particles they contain. Atoms of the same element have the same number of protons, although the same element can differ in the number of neutrons which are then called isotopes of that element. Atoms are electrostatically neutral if they have an equal number of protons and electrons. Atoms which have either gained or lost electrons are called ions. Atoms are the fundamental building blocks of chemistry, and are conserved in chemical reactions. Atoms are able to bond into molecules and other types of chemical compounds. Molecules are made up of multiple atoms; for example, a molecule of water is a combination of two hydrogen and one oxygen atom.

Properties of the atom

Subatomic particles

:see main article subatomic particles Up until 1961, the subatomic particles were thought to consist of only protons, neutrons and electrons. However, protons and neutrons themselves are now known to consist of varieties of a still smaller particle called the quark, and the electron is considered a type of lepton. Therefore in modern atomic theory, the two basic constituents of matter are the lepton and the quark of which the above three particles of the atom are composed. All particles exhibit a wave-particle duality so that the electron is better understood as a wave when drawn about a nucleus. Unlike planets revolving around the sun, the electron is not held around the nucleus of the atom by gravity, but rather by electromagnetism.
Atom sizes
The atom is many times smaller than the wavelength that human vision can detect in any kind of microscope. However, there are ways of projecting the atom so as to obtain amplified images of it. These include: scanning tunneling microscopy (STM), atomic force microscopy (ATM), and nuclear magnetic resonance (NMR). In measuring an atom, the size of the area that an electron can travel in must be determined. Electrons travel in areas called atomic orbitals. This area forms a cloud where the electron may be situated. In the helium atom above (shown in its ground state), the atomic orbital where the electron may be situated describes a sphere. However, the cloud or atomic orbital in which an electron can travel changes shapes depending on the energy of the electron. So some electrons travel in the shape of a dumbbell with the nucleus in the smallest space in-between. There are other more complicated shapes as well. And the heavier the element, the more electrons there are and the more shapes there are for the orbitals in the atom. It therefore not only becomes more complicated to measure the size of the atom, but it becomes complicated to create models of the atoms of heavier elements. Since the electron orbitals are considered clouds, then the size of an atom is not easily defined since the places where the electron can be just gradually go to zero as the distance from the nucleus increases. For atoms that can form solid crystals, the distance between adjacent nuclei can give an estimate of the atom size. For atoms that do not form solid crystals other techniques are used, including theoretical calculations. As an example, the size of a hydrogen atom is estimated to be approximately 1.0586×10 m. Compare this to the size of the proton which is the only particle in the nucleus of the hydrogen atom which is approximately 10 m. Thus the ratio of the sizes of the hydrogen atom to its nucleus is about 100,000:1. Atoms of different elements do vary in size, but the sizes are roughly the same to within a factor of 2 or so. The reason for this is that elements with a large positive charge on the nucleus attract the electrons to the center of the atom more strongly. To illustrate the size of an atom, one million atoms can fit within the breadth of a strand of hair. An atom is mostly space. A basic analogy for the ratio of space inside an atom is this: if an atom were the size of a baseball stadium, the nucleus would be the size of a marble on second base and the electrons would orbit the perimeter.
Elements, isotopes and ions
Atoms are generally classified by their atomic number, which corresponds to the number of protons in the atom. The atomic number defines which element the atom is. For example, carbon atoms are those atoms containing six protons. All atoms with the same atomic number share a wide variety of physical properties and exhibit the same chemical behavior. The various kinds of atoms are listed in the periodic table in order of increasing atomic number. The mass number, atomic mass number, or nucleon number of an element is the total number of protons and neutrons in an atom of that element, because each proton or neutron essentially has a mass of 1 amu. The number of neutrons in an atom has no effect on which element it is. Each element can have numerous different atoms with the same number of protons and electrons, but varying numbers of neutrons. Each has the same atomic number but a different mass number. These are called the isotopes of an element. When writing the name of an isotope, the element name is followed by the mass number. For example, carbon-14 contains 6 protons and 8 neutrons in each atom, for a total mass number of 14. The simplest atom is the hydrogen atom, which has atomic number 1 and consists of one proton and one electron. The hydrogen isotope which also contains one neutron so is called deuterium or hydrogen-2; the hydrogen isotope with two neutrons is called tritium or hydrogen-3. Tritium is an unstable isotope which causes the atom to lose mass in a process called radioactivity. The elements in the periodic table beginning with number 86, radon, and those that follow have no stable isotopes and are all radioactive. The atomic mass listed for each element in the periodic table is an average of the isotope masses found in nature, weighted by their abundance. Although most sources state that there are 92 elements that occur naturally on earth from hydrogen up to uranium in the periodic table, it has been recently discovered that plutonium, the 94th element, also occurs naturally. Most of these elements were created through stellar nucleosynthesis and supernova nucleosynthesis. Several elements that do not occur on earth have been found to be present in stars. Elements not normally found in nature have been artificially created by nuclear bombardment, but they are usually unstable and spontaneously change into stable natural chemical elements by the processes of radioactive decay. Atoms that have either lost or gained electrons are called atomic ions (with either positive(+) or negative charge(−), respectively). Atoms are canonically distinguished from ions by their balanced electrical charge.
Atomic spectrum
:see main article Atomic spectroscopy Each element in the periodic table therefore consists of an atom in a unique configuration i.e. with different amounts of protons in the nucleus. Each atom of each element can also be uniquely described by the shapes of its atomic orbitals and the number of electrons within them. There is also another way in which each element with its own configuration is distinctive, that is, by its atomic spectrum. A spectrum is created when light is passed through a prism and the light breaks up into its component colors. Spectroscopy studies the spectrum of each element. Each atom of each element creates its own light pattern unique to itself, its own spectral signature. Scientists can use a spectrometer to study the atoms in stars and other distant objects, and due to the distinctive spectral lines that each element produces, are able to tell the chemical composition of distant planets, stars and galaxies.
Electron configuration
:see main article electron configuration The chemical behavior of atoms is largely due to interactions between electrons. Electrons of an atom remain within certain, predictable electron configurations. Electrons fall into shells based on their relative energy level. Generally, the higher the energy level of a shell, the further away it is from the nucleus. The electrons in the outermost shell, called the valence electrons, have the greatest influence on chemical behavior. Core electrons (those not in the outer shell) play a role, but it is usually in terms of a secondary effect due to screening of the positive charge in the atomic nucleus. valence electrons of a hydrogen atom. The principal quantum number is at the right of each row and the azimuthal quantum number is denoted by letter at top of each column.]] An electron shell can hold up to 2n² electrons, where n is the number of the shell. Whichever occupied shell is currently most outward is the valence shell, even if it only has one electron. In the most stable state, an atom's electrons will fill up its shells in order of increasing energy. Under some circumstances an electron may be excited to a higher energy level (that is, it absorbs energy from an external source and leaps to a higher shell), leaving a space in a lower shell, but at some point it will fall back to its previous level, emitting its excess energy as a photon. Electron shells also have distinctive shapes denoted by letters. In the illustration, the letters s, p, and d describe the shape of the atomic orbital. Electrons also have another property that describes their configuration due to the fact that they rotate in space. Thus electrons are said to have spin (physics).
Valence and bonding
:see main article valence electrons and chemical bond The number of electrons in an atom's outermost shell (ie the valence shell) governs its bonding behavior. Therefore, elements with the same number of valence electrons are grouped together in the periodic table of the elements. Group (i.e. column) 1 elements contain one electron on their outer shell; Group 2, two electrons; Group 3, three electrons; etc. As a general rule, the fewer electrons in an atom's valence shell, the more reactive it is. Group 1 metals are therefore very reactive, with caesium, rubidium, and francium being the most reactive of all metals. Every atom is much more stable (i.e. less energetic) with a full valence shell. This can be achieved one of two ways: an atom can either share electrons with neighboring atoms (a covalent bond), or it can remove electrons from other atoms (an ionic bond). Another form of ionic bonding involves an atom giving some of its electrons to another atom; this also works because it can end up with a full valence by giving up its entire outer shell. By moving electrons, the two atoms become linked. This is known as chemical bonding and serves to build atoms into molecules or ionic compounds. Five major types of bonds exist:
- ionic bonds;
- covalent bonds;
- coordinate covalent bonds;
- hydrogen bonds; and
- metallic bonds.
Atoms and antimatter
:see main article antimatter Antimatter can also form atoms, composed of antielectrons (positrons), antiprotons, and antineutrons.

Atoms and the Big Bang

In models of the Big Bang, Big Bang nucleosynthesis predicts that within one to three minutes of the Big Bang all the current atomic material in the universe was created producing no heavier element than lithium, but mostly hydrogen and helium. However, although the basic atomic particles of matter were created, atoms themselves could not form in the intense heat. Big Bang chronology of the atom continues to approximately 379,000 years after the Big Bang when the cosmic temperature had dropped to just 3,000 K which allowed the first atoms to form. It was then cool enough to allow protons to capture one electron each and form neutral atoms of hydrogen. Hydrogen makes up approximately 75% of the atoms in the universe. Helium makes up 24% and all other elements make up 1%. Since the size of the universe is unknown, the total numbers of atoms in the universe is unknown, but the number is not thought to be infinite because current theory suggests we live in a finite universe. One thing we can say about the mass of the baryons in the universe, meaning the mass of the protons and neutrons, is that we can tell what the ratio of their density ought to be from the Big Bang model. Einstein's theory of General Relativity suggests that the universe is the same in all directions and from all viewpoints. Therefore, examining one region of the universe and the density of atoms in that region should tell us how densely atoms are scattered throughout the entire universe, but as said previously, does not tell us how far the universe extends and how many atoms exist in total. Big Bang Nucleosynthesis predicts that 1/20 of the total mass of the Universe is baryonic matter. (The baryon is the category used to describe neutrons and protons which are similar in mass but different in electric charge.) So theoretically we should be able to study a region of space and calculate the amount of matter we see through our telescopes and one-twentieth of the matter should be baryons. However, from the density we can see through telescopes of matter in regions of the visible universe, 99% of the baryons are missing. This has given rise to theories of dark matter (which should also be made of baryons--or if you prefer atoms, since baryons make up the nucleus of atoms) in order to make up the difference in missing matter. What that means is that there are probably more atoms out there than we can see through our usual means of detection. In other words, we cannot see visible light from these atoms nor have we detected electromagnetic radiation, but they exist. In fact, in some cases we have detected, through radio-wave detectors, entire galaxies such as Virgo H121 that do not appear in normal telescopes.

Atomic theory

The atomic theory is a theory of the nature of matter. It states that all matter is composed of atoms.

Historical theories

Democritus and Leucippus, Greek philosophers in the 5th century BC, presented the first theory of atoms (see article atomism for more details). They held that each atom had a different shape, like a pebble, that governed the atom's properties. Dalton and Avogadro rediscovered the works of Democritus and Leucippus and suggested in the 19th century that matter was made up of atoms, but they knew nothing of their structure. This theory was conflicting with the theory of infinite divisibility, which states that matter can always be divided into smaller parts. The controversy ended in 1911 when Jean Perrin demonstrated the existence of atoms through experimental validation of Einstein's theory of Brownian motion (which relied on atomic theory). For much of this time, atoms were thought to be the smallest possible piece of matter. However, in 1897, J.J. Thomson published his work proving that cathode rays are made of negatively charged particles (electrons). Since cathode rays are essentially emitted from matter, this proved that atoms are made up of subatomic particles and are therefore divisible, and not the indivisible "atomos" Democritus talked about. Physicists later invented a new term for indivisible units, namely elementary particles since the word atom had already been taken and come into common use. At first, it was believed that the electrons were distributed more or less uniformly in a sea of positive charge (the plum pudding model). However, an experiment conducted a few years later by Rutherford demonstrated that atoms are mostly empty space, with a lot of mass concentrated in a nucleus. In the gold foil experiment, he shot alpha particles (emitted by polonium) through a sheet of gold. He observed that most of the particles passed straight through the sheet without deflection (striking a fluorescent screen on the other side), but that, surprisingly, a small number were bounced right back (having come close to a nucleus). This led to the planetary model of the atom, in which the electrons orbited the nucleus like the planets orbiting the sun. The nucleus was later discovered to contain protons, and further experimentation by Rutherford found that the nuclear mass of most atoms surpassed the number of protons it possessed; this led him to postulate the existence of neutrons, whose existence would be proven in 1932 by James Chadwick. The planetary model of the atom still had shortcomings. Firstly, a moving electrical charge emits electromagnetic waves; according to classical physics, an orbiting charge would steadily lose energy and spiral towards the nucleus, eventually colliding with it. Secondly, the model didn't explain why hydrogen gas, when submitted to an electrical discharge, emitted light only in certain discrete spectra. Experiments by Max Planck and Albert Einstein demonstrated that energy is transferred in tiny fixed amounts known as quanta. In 1913, Niels Bohr used this idea in his Bohr model of the atom, in which the electrons could only orbit the nucleus in fixed circles. They couldn't spiral downwards because they couldn't lose energy in a continuous manner; they could only make quantum leaps between fixed energy levels. The Bohr model would eventually be replaced by a full quantum mechanics model in 1925.

Study of atoms

Because of their ubiquitous nature, atoms have been an important field of study for many centuries. Current research focuses on quantum effects, such as in Bose-Einstein condensate. The study of atoms was done largely by indirect means through the 19th century and early 20th century. In recent years, however, new techniques have made the identification and study of atoms easier and more accurate. The electron microscope, invented in 1931, can image large molecules, however, not the atom itself. Atomic force microscopy is another technique by which individual atoms can be visualized and even arranged into patterns. Methods also exist to identify atoms and compounds. Elemental analysis allows the exact identification of the types and amounts of atoms in a substance.

Practical uses of the atom

Atoms have given us the key to understanding our universe, understanding our earth and life upon it, improving technology, and creating life-saving pharmaceuticals. There does not exist a scientific field that is not affected by the understanding of the atom. Atoms are the basis for chemistry, physics, geology, astronomy and biology. Within the tiny atom are the powers to both create and destroy. Through fusion and fission man has learned to unleash the power of the atom. Our sun and other stars use fusion of the atom to create the heavier elements in the universe that were not created in the Big Bang. Fission of the atom is used to create power in nuclear power plants. Fusion of the atom may one day be used to create safer forms of power than current fuels that are destroying the delicate balance of earth's ecosystem.

External links

- [http://www.howstuffworks.com/atom.htm How Atoms Work] ko:원자 ms:Atom ja:原子 simple:Atom th:อะตอม

Electron shell

In atomic physics, an electron shell is a group of atomic orbitals with the same value of the principal quantum number n. Electron shells make up the electron configuration of an atom. It can be shown that the number of electrons that can reside in a shell is equal to

2n^2

. The existence of electron shells was first observed experimentally in Henry Moseley's X-ray absorption studies. He labelled them with the letters K, L, M, etc. These letters were later found to correspond to the n-values 1, 2, 3, etc. They are used in the spectroscopic Siegbahn notation. The name originates from the Bohr model, in which groups of electrons were believed to orbit the nucleus at certain distances, so that their orbits formed "shells".

References

- Tipler, Paul & Ralph Llewellyn (2003). Modern Physics (4th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-4345-0 Category:Atomic physics Category:Quantum chemistry

Proton

:For alternative meanings see proton (disambiguation). In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1.602 × 10⁻¹⁹ coulomb) and a mass of 938.3 MeV/c² (1.6726 × 10⁻²⁷ kg), or about 1836 times the mass of an electron. The proton is observed to be stable, with a lower limit on its half-life of about 10³⁵ years, although some theories predict that the proton may decay. The proton and neutron are both nucleons. The nucleus of the most common isotope (called protium) of the hydrogen atom is a single proton. The nuclei of other atoms are composed of protons and neutrons held together by the strong nuclear force. The number of protons in the nucleus determines the chemical properties of the atom and which chemical element it is. Protons are classified as baryons and are composed of two up quarks and one down quark, which are also held together by the strong nuclear force, mediated by gluons. The proton's antimatter equivalent is the antiproton, which has the same magnitude charge as the proton but the opposite sign. In chemistry and biochemistry, the term proton may refer to the hydrogen ion, H⁺. In this context, a proton donor is an acid and a proton acceptor a base (see acid-base reaction theories).

History

Ernest Rutherford is generally credited with the discovery of the proton. In 1918 Rutherford noticed that when alpha particles were shot into nitrogen gas, his scintillation detectors showed the signatures of hydrogen nuclei. Rutherford determined that the only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggested that the hydrogen nucleus, which was known to have an atomic number of 1, was an elementary particle. Prior to Rutherford, Eugene Goldstein had observed canal rays, which were composed of positively charged ions.

Technological applications

Protons can exist in spin states. This property is exploited by nuclear magnetic resonance spectroscopy. In NMR spectroscopy, a magnetic field is applied to a substance in order to detect the shielding around the protons in the nuclei of that substance, which is provided by the surrounding electron clouds. Scientists can use this information to then construct the molecular structure of the molecule under study.

Antiproton

The antiproton is the antiparticle of the proton. It was discovered in the year 1955 by Emilio Segre and Owen Chamberlain, for which they were awarded a 1959 Nobel Prize in Physics. CPT-symmetry puts strong constraints on the relative properties of particles and antiparticles and, therefore, is open to stringent tests. For example, the charges of the proton and antiproton must sum to exactly zero. This equality has been tested to one part in 10^-8. The equality of their masses is also tested to better than one part in 10^-8. By holding antiprotons in a Penning trap, the equality of the charge to mass ratio of the proton and the antiproton has been tested to 1 part in 9×10^-11. The magnetic moment of the antiproton has been found with error of 8×10^-3 nuclear Bohr magnetons, and is found to be equal and opposite to that of the proton.

External links

- [http://pdg.lbl.gov/ Particle Data Group] Category:Nucleon ko:양성자 ms:Proton ja:陽子 simple:Proton th:โปรตอน

Nucleus

Nucleus usually refers to the center of something, but can mean:
- atomic nucleus, the collection of protons and neutrons in the center of an atom that carries the bulk of the atom's mass and positive charge
- cell nucleus, the membrane-bound subcellular organelle found in eukaryotes, visible via microscopy, which contains, primarily, the cell's chromosomes
- nucleus (neuroanatomy), a central nervous system structure composed mainly of gray matter that mediates electrical signaling within a particular subsystem
- comet nucleus, the solid core of a comet
- galaxy nucleus, the central region of a galaxy
- ice nucleus, the center of an ice crystal
- cloud condensation nuclei, the basis for the development of a cloud droplet
- syllable nucleus, the central part of a syllable
- sentence nucleus, the syllable which receives the greatest stress in a word
- Nucleus CMS, an open-source weblog system
- Nucleus RTOS, a brand of operating system
- Nucleus (band), a British jazz-rock band led by Ian Carr

Etymology

"Nucleus" is New Latin, the diminutive of the Latin nux (nut). ko:핵 th:นิวเคลียส

Anode

.]] An anode (from the Greek άνοδος = 'going up') is the electrode in a device that electrons flow out of to return to the circuit. Literally, the path through which the electrons ascend out of an electrolyte solution. The other charged electrode in the same cell or device is the cathode. For electrons to flow through the anode a positive charge is applied to the anode (attracting electrons).

Flow of electrons

The flow of electrons is always from anode–to–cathode outside of the cell or device and from cathode–to–anode inside the cell or device regardless of the cell or device type. Inside a chemical cell ions are carrying the electrons but the flow is still from cathode–to–anode inside the cell. (note that in most electronic circuit diagrams current is shown to flow from positive to negative but that the actual electrons in the circuit are flowing OPPOSITE to the electrical current diagram).

Electrolytic anode

In electrochemistry, the anode is where oxidation occurs and is also the negative polarity contact in an electrolytic cell. At the anode anions are forced by the electrical voltage potential to chemically react and give off electrons (oxidation) which then flow up and into the driving circuit.

Battery or galvanic cell anode

In a battery or galvanic cell the anode is the negative contact that electrons flow from through the circuit. Internally the anions are flowing to the anodic material inside the cell which is connected to the negative contact of the cell; but, external to the cell in the circuit electrons are being pushed out through the negative contact and thus through the circuit by the voltage potential of the cell.

Vacuum tube anode

In electronic vacuum devices circuits such as a cathode ray tube, the anode is the positively charged electron collector. In a tube the anode is a charged positive plate that collects the electrons emitted by the cathode through electric attraction.

Diode anode

In a semiconductor diode the anode is the P-doped layer which initially supplies electrons to the junction. In the junction region the electrons supplied by the anode combine with holes supplied from the N-doped region creating a depleted zone. As the P-doped layer supplies electrons to the depleted region, positive dope ions are left behind in the P-doped layer ('P' for positive charge carrier ions). This creates a base charge of positive on the anode. When a positive voltage is applied to anode of the diode from the circuit more electrons are able to be transferred to the depleted region and this causes the diode to become conductive, allowing current to flow through the circuit. The terms anode and cathode should not be applied to a zener diode since it allows flow in either direction based on potential applied to the zener diode.

Sacrificial Anode

In cathodic protection a metal anode that is more reactive to the corrosive environment of the system to be protected is electrically linked to the protected system and partially corrodes or dissolves which protects the metal of the system it is connected to. As an example an iron or steel ship's hull may be protected by a zinc sacrificial anode which will dissolve into the seawater and prevent the hull from being corroded. Sacrificial anodes are particularly needed for systems where a static charge is generated by the action of flowing liquids, such as pipelines and watercraft.

Related antonym

The opposite of an anode is a cathode. When the charge on the system is reversed the electrodes switch functions and anode becomes cathode, while cathode becomes anode as long as the reversed charge is applied.

Polyatomic

Polyatomic ions are groups of atoms that usualyl stay together and carry an overall ionic charge. For example, a nitrate ion, NO3. The nitrate ion has one nitrogen atom tightly bonded to three oxygen atoms. The ionic charge is 1-.

Oxygen

Oxygen is a chemical element in the periodic table. It has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe, usually covalently bonded with other elements. Unbound oxygen (usually called molecular oxygen, O₂, a diatomic molecule) first appeared on Earth during the Paleoproterozoic era (between 2500 million years ago and 1600 million years ago) and as a product of the metabolic action of early anaerobes (archaea and bacteria). The presence of free oxygen drove most of the organisms then living to extinction. The atmospheric abundance of free oxygen in later geological epochs and up to the present has been largely driven by photosynthetic organisms, roughly three quarters by phytoplankton and algae in the oceans and one quarter from terrestrial plants.

Characteristics

At standard temperature and pressure, oxygen is mostly found as a gas consisting of a diatomic molecule with the chemical formula O₂. O₂ has two energetic forms:
- The low-energy predominant single-bonded diradical triplet oxygen. This native diradical quality of oxygen contributes to its destructive chemical nature. This form is stabilized by the degeneracy effect.
- The high-energy double-bonded molecule singlet oxygen. Oxygen is a major component of air, produced by plants during photosynthesis, and is necessary for aerobic respiration in animals. The word oxygen derives from two words in Greek, οξυς (oxys) (acid, sharp) and γεινομαι (geinomai) (engender). The name "oxygen" was chosen because, at the time it was discovered in the late 18th century, it was believed that all acids contained oxygen. The definition of acid has since been revised to not require oxygen in the molecular structure. Liquid O₂ and solid O₂ have a light blue color and both are highly paramagnetic. Liquid O₂ is usually obtained by the fractional distillation of liquid air. Liquid and solid O₃ (ozone) have a deeper color of blue. A recently discovered allotrope of oxygen, tetraoxygen (O₄), is a deep red solid that is created by pressurizing O₂ to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O₂ or O₃.

Applications

Liquid oxygen finds use as an oxidizer in rocket propulsion. Oxygen is essential to respiration, so oxygen supplementation has found use in medicine (as oxygen therapy). People who climb mountains or fly in airplanes sometimes have supplemental oxygen supplies (as air). Oxygen is used in welding (such as the oxyacetylene torch), and in the making of steel and methanol. Oxygen presents two absorption bands centered in the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming from vegetation canopies in those oxygen bands to characterize plant health status from a satellite platform. This is because in those bands, it is possible to discriminate the vegetation's reflectance from the vegetation's fluorescence, which is much weaker. The measurement presents several technical difficulties due to the low signal to noise ratio and due to the vegetation's architecture, but it has been proposed as possibility to monitor the carbon cycle from satellite, thus in a global scale. Oxygen, as a mild euphoric, has a history of recreational use that extends into modern times. Oxygen bars can be seen at parties to this day. In the 19th century, oxygen was often mixed with nitrous oxide to promote an analgesic effect; indeed, such a mixture (Entonox) is commonly used in medicine today.

History

Oxygen was first discovered by Michał Sędziwój, Polish alchemist and philosopher in late 16th century. Sędziwój assumed the existence of oxygen by warming nitre (saltpeter). He thought of the gas given off as "the elixir of life". Oxygen was again discovered by the Swedish pharmacist Carl Wilhelm Scheele sometime before 1773, but the discovery was not published until after the independent discovery by Joseph Priestley on August 1, 1774, who called the gas dephlogisticated air (see phlogiston theory). Priestley published his discoveries in 1775 and Scheele in 1777; consequently Priestley is usually given the credit. It was named by Antoine Laurent Lavoisier after Priestley's publication in 1775.

Occurrence

Oxygen is the second most common component of the earth's atmosphere (20.947% by volume).

Compounds

Due to its electronegativity, oxygen forms chemical bonds with almost all other elements (which is the origin of the original definition of oxidation). The only elements to escape the possibility of oxidation are a few of the noble gases. The most famous of these oxides is dihydrogen monoxide, or water (H₂O). Other well known examples include compounds of carbon and oxygen, such as carbon dioxide (CO₂), alcohols (R-OH), aldehydes, (R-CHO), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO₃⁻), perchlorates (ClO₄⁻), chromates (CrO₄²⁻), dichromates (Cr₂O₇²⁻), permanganates (MnO₄⁻), and nitrates (NO₃⁻) are strong oxidizing agents in and of themselves. Many metals such as iron bond with oxygen atoms, iron (III) oxide (Fe₂O₃). Ozone (O₃) is formed by electrostatic discharge in the presence of molecular oxygen. A double oxygen molecule (O₂)₂ is known and is found as a minor component of liquid oxygen. Epoxides are ethers in which the oxygen atom is part of a ring of three atoms.

Isotopes

Oxygen has fifteen known isotopes with atomic masses ranging from 12 to 26. Three of them are stable and twelve are radioactive. The radioisotopes all have half lives of less than three minutes. The stable isotopes have mass numbers of 16, 17 and 18, of which oxygen-16 is the most common (over 99%).

Precautions

Oxygen can be toxic at elevated partial pressures (i.e. high relative concentrations). This is important in some forms of scuba diving, such as with a rebreather. Certain derivatives of oxygen, such as ozone (O₃), singlet oxygen, hydrogen peroxide, hydroxyl radicals and superoxide, are also highly toxic. The body has developed mechanisms to protect against these toxic species. For instance, the naturally-occurring glutathione can act as an antioxidant, as can bilirubin which is normally a breakdown product of hemoglobin. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels. This is true as well of compounds of oxygen such as chlorates, perchlorates, dichromates, etc. Compounds with a high oxidative potential can often cause chemical burns. The fire that killed the Apollo 1 crew on a test launchpad spread so rapidly because the pure oxygen atmosphere was at normal atmospheric pressure instead of the one third pressure that would be used during an actual launch. (See partial pressure.) Oxygen derivatives are prone to form free radicals, especially in metabolic processes. Because they can cause severe damage to cells and their DNA, they are thought to be related to cancer and aging.

References

- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://physics.nist.gov/cgi-bin/AtData/main_asd Nist atomic spectra database]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes Fourteenth Edition]: Chart of the Nuclides, General Electric Company, 1989

External links

- [http://www.priestleysociety.net Priestley Society, Dedicated to Joseph Priestley the man who discovered oxygen]
- [http://www.best-home-remedies.com/minerals/oxygen.htm Oxygen - Benefits, Deficiency Symptoms And Food Sources]
- [http://www.josephpriestley.info Joseph Priestley Information Website, about the man who discovered oxygen]
- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://www.webelements.com/webelements/elements/text/O/index.html WebElements.com – Oxygen]
- [http://education.jlab.org/itselemental/ele008.html It's Elemental – Oxygen]
- [http://members.tripod.com/tjaartdb0/html/oxygen_toxicity.html Oxygen Toxicity]
- [http://www.uigi.com/oxygen.html Oxygen (O2) Properties, Uses, Applications]
- [http://www.compchemwiki.org/index.php?title=Oxygen Computational Chemistry Wiki]
- [http://koti.mbnet.fi/antitz/dime/en Tests with liquid oxygen :-)] Category:Nonmetals Category:Chalcogens als:Sauerstoff ko:산소 ms:Oksigen ja:酸素 simple:Oxygen th:ออกซิเจน

Hydrogen

|- | Critical temperature || 32.19 K |- | Critical pressure || 1.315 MPa |- | Critical density || 30.12 g/L (Bohr radius) Hydrogen (Latin: hydrogenium, from Greek: hydro: water, genes: forming) is a chemical element in the periodic table that has the symbol H and atomic number 1. At standard temperature and pressure it is a colorless, odorless, nonmetallic, univalent, highly flammable diatomic gas. Hydrogen is the lightest and most abundant element in the universe. It is present in water, all organic compounds (rare exceptions exist, like buckminsterfullerene) and in all living organisms. Hydrogen is able to react chemically with most other elements. Stars in their main sequence are overwhelmingly composed of hydrogen in its plasma state. The element is used in ammonia production, as a lifting gas, as an alternative fuel, and more recently as a power source of fuel cells. Despite its ubiquity in the universe, hydrogen is surprisingly hard to produce in large quantities on the Earth. In the laboratory, the element is prepared by the reaction of acids on metals such as zinc. The electrolysis of water is a simple method of producing hydrogen, but is economically inefficient for mass production. Large-scale production is usually achieved by steam reforming natural gas. Scientists are now researching new methods for hydrogen production; if they succeed in developing a cost-efficient method of large-scale production, hydrogen may become a viable alternative to greenhouse-gas-producing fossil fuels. One of the methods under investigation involves use of green algae; another promising method involves the conversion of biomass derivatives such as glucose or sorbitol at low temperatures using a catalyst. Yet another method is the "steaming" of Carbon, whereby hydrocarbons are broken down with heat to release hydrogen.

Basic features

Hydrogen is the lightest chemical element; its most common isotope comprises just one negatively charged electron, distributed around a positively charged proton (the nucleus of the atom). The electron is bound to the proton by the Coulomb force, the electrical force that one stationary, electrically charged nanoparticle exerts on another. The hydrogen atom has special significance in quantum mechanics as a simple physical system for which there is an exact solution to the Schrödinger equation; from that equation, the experimentally observed frequencies and intensities of the hydrogen's spectral lines can be calculated. Spectral lines are dark or bright lines in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. At standard temperature and pressure, hydrogen forms a diatomic gas, H₂, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under extreme pressures, such as those at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the extremely low pressure in space—virtually a vacuum—the element tends to exist as individual atoms, simply because there is no way for them to combine. However, clouds of H₂ and singular hydrogen atoms are said to form in H I and H II regions and are associated with star formation, however the existence of singular hydrogen atoms is disputed.. Hydrogen plays a vital role in powering stars through the proton–proton and carbon–nitrogen cycle. These are nuclear fusion processes, which release huge amounts of energy in stars and other hot celestial bodies as hydrogen atoms combine into helium atoms. H₂ is highly soluble in water, alcohol, and ether. It has a high capacity for adsorption, in which it is attached to and held to the surface of some substances. It is an odorless, tasteless, colorless, and highly flammable gas that burns at concentrations as low as 4% H₂ in air. It reacts violently with chlorine and fluorine, forming hydrohalic acids that can damage the lungs and other tissues. When mixed with oxygen, hydrogen explodes on ignition. A unique property of hydrogen is that its flame is completely invisible in air. This makes it difficult to tell if a leak is burning, and carries the added risk that it is easy to walk into a hydrogen fire inadvertently. See also: hydrogen atom.

Applications

Large quantities of hydrogen are needed in the chemical and petrolium industries, notably in the Haber process for the production of ammonia, which by mass ranks as the world's fifth most highly produced industrial compound. Hydrogen is used in the hydrogenation of fats and oils (into items such as margarine), and in the production of methanol. Hydrogen is used in hydrodealkylation, hydrodesulfurization, and hydrocracking. The element has several other important uses.
- The element is used in the manufacture of hydrochloric acid, in welding processes, and in the reduction of metallic ores.
- It is an ingredient in rocket fuels.
- It is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas.
- Liquid hydrogen is used in cryogenic research, including superconductivity studies.
- Since hydrogen is 14.5 times lighter than air, it was once widely used as a lifting agent in balloons and airships. However, this use was curtailed when the Hindenburg disaster convinced the public that the gas was too dangerous for this purpose.
- Deuterium, an isotope of hydrogen (hydrogen-2), is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.
- Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints. There are no "hydrogen wells" or "hydrogen mines" on Earth, so hydrogen cannot be considered a primary energy source like fossil fuels or uranium. Hydrogen can however be burned in internal combustion engines, an approach advocated by BMW's experimental hydrogen car. However, it is currently difficult and dangerous to store and handle in sufficient quantity for motor fuel use. Hydrogen fuel cells are being investigated as mobile power sources with lower emissions than hydrogen-burning internal combustion engines. The low emissions of hydrogen in internal combustion engines and fuel cells are currently offset by the pollution created by hydrogen production. This may change if the substantial amounts of electricity required for water electrolysis can be generated primarily from low pollution sources such as nuclear energy or wind. Research is being conducted on hydrogen as a replacement for fossil fuels. It could become the link between a range of energy sources, carriers and storage. Hydrogen can be converted to and from electricity (solving the electricity storage and transport issues), from bio-fuels, and from and into natural gas and diesel fuel. All of this can theoretically be achieved with zero emissions of CO₂ and toxic pollutants.

History

Hydrogen was first produced by Theophratus Bombastus von Hohenheim (1493–1541)—also known as Paracelsus—by mixing metals with acids. He was unaware that the explosive gas produced by this chemical reaction was hydrogen. In 1671, Robert Boyle described the reaction between two iron fillings and dilute acids, which results in the production of gaseous hydrogen. In 1766, Henry Cavendish was the first to recognize hydrogen as a discrete substance, by identifying the gas from this reaction as "inflammable" and finding that the gas produces water when burned in air. Cavendish stumbled on hydrogen when experimenting with acids and mercury. Although he wrongly assumed that hydrogen was a compound of mercury—and not of the acid—he was still able to accurately describe several key properties of hydrogen. Antoine Lavoisier gave the element its name and proved that water is composed of hydrogen and oxygen. One of the first uses of the element was for balloons. The hydrogen was obtained by mixing sulfuric acid and iron. Harold C. Urey discovered Deuterium, an isotope of hydrogen, by repeated distilling the same sample of water. For this discovery, Urey received the Nobel prize for in 1934. In the same year, the third isotope, tritium, was discovered. Because of its relatively simple structure, hydrogen has often been used in models of how an atom works.

Electron energy levels

The ground state energy level of the electron in a Hydrogen atom is 13.6 eV, which is equivalent to an ultraviolet photon of roughly 92 nm. With the Bohr Model the energy levels of Hydrogen can be calculated fairly accurately. This is done by modeling the electron as revolving around the proton, much like the earth revolving around the sun. Except the sun holds earth in orbit with the force of gravity, but the proton holds the electron in orbit with the force of electromagnetism. Another difference between the Earth-Sun system and the Electron-Proton system is that, in this model, due to quantum mechanics the electron is allowed to only be at very specific distances from the proton. Modeling the hydrogen atom in this fashion yields the correct energy levels and spectrum.

Occurrence

quantum mechanics.]] Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance in stars and gas giant planets. It is very rare in the Earth's atmosphere (1 ppm by volume), because being the lightest gas causes it to escape Earth's gravity, though when compounds are considered, it is the tenth most abundant element on Earth. The most common source for this element on Earth is water, which is composed two parts hydrogen to one part oxygen (H₂O). Other sources include most forms of organic matter (currently all known life forms) including coal, natural gas, and other fossil fuels. Methane (CH₄) is an increasingly important source of hydrogen. Throughout the Universe, hydrogen is mostly found in the plasma state whose properties are quite different to molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity, even when the gas is only partially ionised. The charged particles are highly influenced by magnetic and electric fields, for example, in the Solar Wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen can be prepared in several different ways: steam on heated carbon, hydrocarbon decomposition with heat, reaction of a strong base in an aqueous solution with aluminium, water electrolysis, or displacement from acids with certain metals. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas. At high temperatures (700–1100 °C), steam reacts with methane to yield carbon monoxide and hydrogen. :CH₄ + H₂O → CO + 3 H₂ Additional hydrogen can be recovered from the carbon monoxide through the water-gas shift reaction: :CO + H₂O → CO₂ + H₂

Compounds

The lightest of all gases, hydrogen combines with most other elements to form compounds. Hydrogen has an electronegativity of 2.2, so it forms compounds where it is the more nonmetallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H^- ions or just as a solute within the other element (as in palladium hydride). The latter tend to be covalent, since the H⁺ ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. These both form acids. Thus even in an acidic solution one sees ions like hydronium (H₃O⁺) as the protons latch on to something. Although exotic on earth, one of the most common ions in the universe is the H₃⁺ ion. Hydrogen combines with oxygen to form water, H₂O, and releases a lot of energy in doing so, burning explosively in air. Deuterium oxide, or D₂O, is commonly referred to as heavy water. Hydrogen also forms a vast array of compounds with carbon. Because of their association with living things, these compounds are called organic compounds, and the study of the properties of these compounds is called organic chemistry. organic chemistry

Forms

Under normal conditions, hydrogen gas is a mix of two different kinds of molecules which differ from one another by the relative spin of the nuclei. These two forms are known as ortho- and para-hydrogen (this is different from isotopes, see below). In ortho-hydrogen the nuclear spins are parallel (form a triplet), while in para they are antiparallel (form a singlet). At standard conditions hydrogen is composed of about 25% of the para form and 75% of the ortho form (the so-called "normal" form). The equilibrium ratio of these two forms depends on temperature, but since the ortho form has higher energy (is an excited state), it cannot be stable in its pure form. In low temperatures (around boiling point), the equilibrium state is comprised almost entirely of the para form. The conversion process between the forms is slow, and if hydrogen is cooled down and condensed rapidly, it contains large quantities of the ortho form. It is important in preparation and storage of liquid hydrogen, since the ortho-para conversion produces more heat than the heat of its evaporation, and a lot of hydrogen can be lost by evaporation in this way during several days after liquefying. Therefore, some catalysts of the ortho-para conversion process are used during hydrogen cooling. The two forms have also slightly different physical properties. For example, the melting and boiling points of parahydrogen are about 0.1 K lower than of the "normal" form.

Isotopes

Hydrogen is the only element that has different names for its isotopes. (During the early study of radioactivity, various heavy radioactive isotopes were given names, but such names are no longer used, although one element, radon, has a name that originally applied to only one of its isotopes.) The symbols D and T (instead of ²H and ³H) are sometimes used for deuterium and tritium, although this is not officially sanctioned. (The symbol P is already in use for phosphorus and is not available for protium.) ;¹H The most common isotope of hydrogen, this stable isotope has a nucleus consisting of a single proton; hence the descriptive, although rarely used, name protium. The spin of a protium atom is 1/2+. ;²H The other stable isotope is deuterium, with an extra neutron in the nucleus. Deuterium comprises 0.0184%–0.0082% of all hydrogen (IUPAC); ratios of deuterium to protium are reported relative to the VSMOW standard reference water. The spin of a deuterium atom is 1+. ;³H The third naturally occurring hydrogen isotope is the radioactive tritium. The tritium nucleus contains two neutrons in addition to the proton. It decays through beta decay and has a half-life of 12.32 years. Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. Like ordinary hydrogen, tritium reacts with the oxygen in the atmosphere to form T₂O. This radioactive "water" molecule constantly enters the Earth's seas and lakes in the form of slightly radioactive rain, but its half-life is short enough to prevent a buildup of hazardous radioactivity. The spin of a tritium atom is 1/2+. ;⁴H Hydrogen-4 was synthesized by bombarding tritium with fast-moving deuterium nuclei. It decays through neutron emission and has a half-life of 9.93696x10^-23 seconds. The spin of a hydrogen-4 atom is 2-. ;⁵H In 2001 scientists detected hydrogen-5 by bombarding a hydrogen target with heavy ions. It decays through neutron emission and has a half-life of 8.01930x10^-23 seconds. ;⁶H Hydrogen-6 decays through triple neutron emission and has a half-life of 3.26500^-22 seconds. ;⁷H In 2003 hydrogen-7 was created ([http://physicsweb.org/articles/news/7/3/3 article]) at the RIKEN laboratory in Japan by colliding a high-energy beam of helium-8 atoms with a cryogenic hydrogen target and detecting tritons—the nuclei of tritium atoms—and neutrons from the breakup of hydrogen-7, the same method used to produce and detect hydrogen-5.

References

# # # # # #
- [http://www.riken.go.jp/engn/r-world/research/lab/wako/ribeam/ RIKEN Beam Science Laboratory, Japan - Heavy hydrogen research]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes] Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989 ;Book references:
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External links

- [http://www.hydropole.ch/Hydropole/Intro/Phasediag.gif Hydrogen phase diagram.]
- [http://www.compchemwiki.org/index.php?title=Hydrogen Computational Chemistry Wiki] Category:Nonmetals Category:Fuels Category:Chemical elements ko:수소 ms:Hidrogen ja:水素 simple:Hydrogen th:ไฮโดรเจน

Oxygen

Characteristics

Applications

History

Occurrence

Oxygen is the second most common component of the earth's atmosphere (20.947% by volume).

Compounds

Isotopes

Precautions

References

External links

Plasma

:This article is about plasma in the sense of an ionized gas. For other uses of the term, such as blood plasma, see plasma (disambiguation). plasma (disambiguation) In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. "Ionized" in this case means that at least one electron has been removed from a significant fraction of the molecules. The free electric charges make the plasma electrically conductive so that it couples strongly to electromagnetic fields. This fourth state of matter was first identified by Sir William Crookes in 1879 and dubbed "plasma" by Irving Langmuir in 1928, because it reminded him of a blood plasma [http://www.plasmacoalition.org/what.htm].

Common plasmas

blood plasma Plasmas are the most common phase of matter. The entire visible universe outside the Solar System is plasma, since all we can see are stars. Since the space between the stars is filled with a plasma, although a very sparse one (see interstellar- and intergalactic medium), essentially the entire volume of the universe is plasma. In the Solar System, the planet Jupiter accounts for most of the non-plasma, only about 0.1% of the mass and 10⁻¹⁵ of the volume within the orbit of Pluto. Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of a plasma (see dusty plasmas). Commonly encountered forms of plasma include:
- Artificially produced
- Inside fluorescent lamps (low energy lighting), neon signs
- Rocket exhaust
- The area in front of a spacecraft's heat shield during reentry into the atmosphere
- Fusion energy research
- The electric arc in an arc lamp or an arc welder
- Plasma ball (sometimes called a plasma sphere or plasma globe)
- Earth plasmas
- Flames (ie. fire)
- Lightning
- The ionosphere
- The polar aurorae
- Space and astrophysical
- The Sun and other stars (which are plasmas heated by nuclear fusion)
- The solar wind
- The Interplanetary medium (the space between the planets)
- The Interstellar medium (the space between star systems)
- The Intergalactic medium (the space between galaxies)
- The Io-Jupiter flux-tube
- Accretion disks
- Interstellar nebulae

Characteristics

The term plasma is generally reserved for a system of charged particles large enough to behave as one. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e. respond to magnetic fields and be highly electrically conductive). In technical terms, the typical characteristics of a plasma are: # Debye screening lengths that are short compared to the physical size of the plasma. # Large number of particles within a sphere with a radius of the Debye length. # Mean time between collisions usually is long when compared to the period of plasma oscillations.

Plasma scaling

Plasmas and their characteristics exist over a wide range of scales (ie. they are scaleable over many orders of magnitude). The following chart deals only with conventional atomic plasmas and not other exotic phenomena, such as, quark gluon plasmas:

	Typical plasma scaling ranges: orders of magnitude (OOM)
Characteristic	Terrestrial plasmas	Cosmic plasmas
Size in metres (m)	10⁻⁶ m (lab plasmas) to: 10² m (lightning) (~8 OOM)	10⁻⁶ m (spacecraft sheath) to 10²⁵ m (intergalactic nebula) (~31 OOM)
Lifetime in seconds (s)	10⁻¹² s (laser-produced plasma) to: 10⁷ s (fluorescent lights) (~19 OOM)	10¹ s (solar flares) to: 10¹⁷ s (intergalactic plasma) (~17 OOM)
Density in particles per cubic metre	10⁷ to: 10²¹ (inertial confinement plasma)	10³⁰ (stellar core) to: 10⁰ (i.e., 1) (intergalactic medium)
Temperature in kelvins (K)	~0 K (Crystalline non-neutral plasma[http://sdphca.ucsd.edu/]) to: 10⁸ K (magnetic fusion plasma)	10² K (aurora) to: 10⁷ K (Solar core)
Magnetic fields in teslas (T)	10⁻⁴ T (Lab plasma) to: 10³ T (pulsed-power plasma)	10⁻¹² T (intergalactic medium) to: 10⁷ T (Solar core)

Temperatures

plasma scaling characteristic of the gas being excited.]] The defining characteristic of a plasma is ionization. Although ionization can be caused by UV radiation, energetic particles, or strong electric fields, (processes that tend to result in a non-Maxwellian electron distribution function), it is more commonly caused by heating the electrons in such a way that they are close to thermal equilibrium so the electron temperature is relatively well-defined. Because the large mass of the ions relative to the electrons hinders energy transfer, it is possible for the ion temperature to be very different from (usually lower than) the electron temperature. The degree of ionization is determined by the electron temperature relative to the ionization energy (and more weakly by the density) in accordance with the Saha equation. If only a small fraction of the gas molecules are ionized (for example 1%), then the plasma is said to be a cold plasma, even though the electron temperature is typically several thousand degrees. The ion temperature in a cold plasma is often near the ambient temperature. Because the plasmas utilized in plasma technology are typically cold, they are sometimes called technological plasmas. They are often created by using a very high electric field to accelerate electrons, which then ionize the atoms. The electric field is either capacitively or inductively coupled into the gas by means of a plasma source, e.g. microwaves. Common applications of cold plasmas include plasma-enhanced chemical vapor deposition<