question: plasma" is just ionized gas, yet it is regarded as a "different state of matter"...why aren't ionized liquids or solids considered different states of matter?
comment: Plasmas are gasses where some of the electrons have been pulled completely away from the nucleus of the individual atoms, whereas an ionized gas is one where the atoms have metely gained or lost an electron. The free flowing electrons in a plasma give it electrical and magnetic properties that simply ionized gasses won't have. You can use a magnetic field to move or contain a plasma but it will have no effect on an ionized gas. Plasma can also conduct electricity and generate magnetic fields, ionized gas can't. Plasmas also generate light when excited by electricity, neon and florescent bulbs use this property and it is why we can see the track of lightning.
passages: Plasma and ionized gases have properties and display behaviours unlike those of the other states, and the transition between them is mostly a matter of nomenclature and subject to interpretation. Based on the surrounding environmental temperature and density, partially ionized or fully ionized forms of plasma may be produced. Neon signs and lightning are examples of partially ionized plasma. The Earth's ionosphere is a plasma and the magnetosphere contains plasma in the Earth's surrounding space environment. The interior of the Sun is an example of fully ionized plasma, along with the solar corona and stars.
   Plasma is often called the "fourth state of matter" after solid, liquids and gases. It is distinct from these and other lower-energy states of matter. Although it is closely related to the gas phase in that it also has no definite form or volume, it differs in a number of ways, including the following:
  
  Section::::Resistivity and conductivity of various materials.
  
  BULLET::::- A conductor such as a metal has high conductivity and a low resistivity.
  
  BULLET::::- An insulator like glass has low conductivity and a high resistivity.
   Section::::Properties and parameters.:Comparison of plasma and gas phases.
  
  Plasma is often called the "fourth state of matter" after solid, liquids and gases, despite plasma typically being an ionized gas. It is distinct from these and other lower-energy states of matter. Although it is closely related to the gas phase in that it also has no definite form or volume, it differs in a number of ways, including the following:
  
  Section::::Plasmas in space science and astronomy.
  
  Plasmas are by far the most common phase of ordinary matter in the universe, both by mass and by volume.
   The word "plasma" comes or 'jelly', and describes the behaviour of the ionized atomic nuclei and the electrons within the surrounding region of the plasma. Very simply, each of these nuclei are suspended in a movable sea of electrons. Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879 (he called it "radiant matter"). The nature of this "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897.
   Section::::Mathematical descriptions.
  
  To completely describe the state of a plasma, all of the
  
  particle locations and velocities that describe the electromagnetic field in the plasma region would need to be written down.
  
  However, it is generally not practical or necessary to keep track of all the particles in a plasma.
  
  Therefore, plasma physicists commonly use less detailed descriptions, of which
  
  there are two main types:
  
  Section::::Mathematical descriptions.:Fluid model.
   Plasma is a state of matter in which an ionized gaseous substance becomes highly electrically conductive to the point that long-range electric and magnetic fields dominate the behaviour of the matter. The plasma state can be contrasted with the other states: solid, liquid, and gas.
   Like a gas, plasma does not have definite shape or volume. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Positively charged nuclei swim in a "sea" of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal, where this electron "sea" allows matter in the plasma state to conduct electricity.
   A gas is usually converted to a plasma in one of two ways, e.g., either from a huge voltage difference between two points, or by exposing it to extremely high temperatures. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons. This creates a so-called partially ionised plasma. At very high temperatures, such as those present in stars, it is assumed that essentially all electrons are "free", and that a very high-energy plasma is essentially bare nuclei swimming in a sea of electrons. This forms the so-called fully ionised plasma.
   For plasma to exist, ionisation is necessary. The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The degree of ionisation of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled by the electron and ion temperatures and electron-ion vs electron-neutral collision frequencies. The degree of ionisation, formula_1, is defined as formula_2, where formula_3 is the number density of ions and formula_4 is the number density of neutral atoms. The "electron density" is related to this by the average charge state formula_5 of the ions through formula_6, where formula_7 is the number density of electrons.
   BULLET::::- "Nonthermal plasmas" on the other hand are non-equilibrium ionized gases, with two temperatures: ions and neutrals stay at a low temperature (sometimes room temperature), whereas electrons are much hotter. (formula_14). A kind of common nonthermal plasma is the mercury-vapor gas within a fluorescent lamp, where the "electrons gas" reaches a temperature of 10,000 kelvins while the rest of the gas stays barely above room temperature, so the bulb can even be touched with hands while operating.
   BULLET::::- A "partially" or "weakly ionized gas" means the plasma is not dominated by Coulomb collisions, i.e. when formula_13.
  
  Most of "technological" (engineered) plasmas are weakly ionized gases.
  
  Section::::Properties and parameters.:Temperature.:Thermal vs. nonthermal (cold) plasmas.
  
  Based on the relative temperatures of the electrons, ions and neutrals, plasmas are classified as "thermal" or "non-thermal" (also referred to as "cold plasmas").
  
  BULLET::::- "Thermal plasmas" have electrons and the heavy particles at the same temperature, i.e. they are in thermal equilibrium with each other.
   In 1913, Birkeland may have been the first to predict that plasma was ubiquitous in space. He wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in 'empty' space."
   BULLET::::- Gas: A compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.
  
  BULLET::::- Plasma: Free charged particles, usually in equal numbers, such as ions and electrons. Unlike gases, plasmas may self-generate magnetic fields and electric currents, and respond strongly and collectively to electromagnetic forces.
  
  Section::::Low-energy states.:Modern states.
  
  BULLET::::- Excitonium
  
  BULLET::::- Degenerate matter: matter under very high pressure, supported by the Pauli exclusion principle.
  
  BULLET::::- Electron-degenerate matter: found inside white dwarf stars. Electrons remain bound to atoms but are able to transfer to adjacent atoms.
   In a chemical equation, the state of matter of the chemicals may be shown as (s) for solid, (l) for liquid, and (g) for gas. An aqueous solution is denoted (aq). Matter in the plasma state is seldom used (if at all) in chemical equations, so there is no standard symbol to denote it. In the rare equations that plasma is used in plasma is symbolized as (p).
  
  Section::::Non-classical states.
  
  Section::::Non-classical states.:Glass.
   Classically, states of matter are distinguished by changes in the properties of matter related to external factors such as pressure and temperature. States are usually distinguished by a discontinuity in one of those properties: for example, raising the temperature of ice produces a clear discontinuity at 0 °C as energy goes into phase transition, instead of temperature increase. The classical states of matter are usually summarised as: solid, liquid, gas, and plasma. In the 20th century, increased understanding of the more exotic properties of matter resulted in the identification of many additional states of matter, none of which are observed in normal conditions.
   Historically, the distinction is made based on qualitative differences in properties. Matter in the solid state maintains a fixed volume and shape, with component particles (atoms, molecules or ions) close together and fixed into place. Matter in the liquid state maintains a fixed volume, but has a variable shape that adapts to fit its container. Its particles are still close together but move freely. Matter in the gaseous state has both variable volume and shape, adapting both to fit its container. Its particles are neither close together nor fixed in place. Matter in the plasma state has variable volume and shape, and contains neutral atoms as well as a significant number of ions and electrons, both of which can move around freely.
   In most cases the electrons are close enough to thermal equilibrium that their temperature is relatively well-defined; this is true even when there is a significant deviation from a Maxwellian energy distribution function, for example, due to UV radiation, energetic particles, or strong electric fields. Because of the large difference in mass, the electrons come to thermodynamic equilibrium amongst themselves much faster than they come into equilibrium with the ions or neutral atoms. For this reason, the ion temperature may be very different from (usually lower than) the electron temperature. This is especially common in weakly ionized technological plasmas, where the ions are often near the ambient temperature.
   Section::::Properties and parameters.:Temperature.
  
  Plasma temperature is commonly measured in kelvin or electronvolts and is, informally, a measure of the thermal kinetic energy per particle. High temperatures are usually needed to sustain ionisation, which is a defining feature of a plasma. The degree of plasma ionisation is determined by the electron temperature relative to the ionization energy (and more weakly by the density), in a relationship called the Saha equation. At low temperatures, ions and electrons tend to recombine into bound states—atoms—and the plasma will eventually become a gas.
   The plasma state is often misunderstood, and although not freely existing under normal conditions on Earth, it is quite commonly generated by either lightning, electric sparks, fluorescent lights, neon lights or in plasma televisions. The Sun's corona, some types of flame, and stars are all examples of illuminated matter in the plasma state.
  
  Section::::Phase transitions.
   A particular case of fully ionizes gases are very hot thermonuclear plasmas, such as plasmas artificially produced in nuclear explosions or naturally formed in our Sun and all stars in the universe. Stars contain largely hydrogen and helium gases, that are "fully ionized" into electrons, protons (H) and helium ions (He). Equations to characterize such very hot, fully ionized thermonuclear plasmas in the presence of stellar magnetic fields can be approximated to ideal magnetohydrodynamics laws with high magnetic Reynolds number.
  
  Section::::History.
   Even if the macroscopic electric field is zero, any single ion will experience an electric field due to the neighboring charged particles in the plasma. This results in a broadening of some lines that can be used to determine the density of the plasma.
  
  Section::::Passive spectroscopy.:Spectral line ratios.
  
  The brightness of an atomic spectral line emitted by atoms and ions in a gas (or plasma) can depend on the gas's temperature and pressure.
   Section::::Complex plasma phenomena.:Non-neutral plasma.
  
  The strength and range of the electric force and the good conductivity of plasmas usually ensure that the densities of positive and negative charges in any sizeable region are equal ("quasineutrality"). A plasma with a significant excess of charge density, or, in the extreme case, is composed of a single species, is called a non-neutral plasma. In such a plasma, electric fields play a dominant role. Examples are charged particle beams, an electron cloud in a Penning trap and positron plasmas.
  
  Section::::Complex plasma phenomena.:Dusty plasma/grain plasma.
   In general, for multicomponent plasmas one defines the coupling parameter for each species "s" separately:
  
  Here, "s" stands for either electrons or (a type of) ions.
  
  Section::::The ideal plasma approximation.
  
  One of the criteria which determine whether a collection of charged particles can rigorously be termed an ideal plasma is that Λ»1.
   Section::::Plasma.
  
  The coupling constant of a plasma is given by the ratio of its average Coulomb-interaction energy to its average kinetic energy—or how strongly the electric force of each atom holds the plasma together . Plasmas can therefore be categorized into weakly- and strongly-coupled plasmas depending upon the value of this ratio. Many of the typical classical plasmas, such as the plasma in the solar corona, are weakly coupled, while the plasma in a white dwarf star is an example of a strongly coupled plasma.
  
  Section::::Quantum mechanics.
  
  Two coupled quantum systems can be modeled by a Hamiltonian of the formformula_5
   Plasma is composed of gaseous matter that has been completely ionized, usually through high temperature.
  
  Section::::Modern principles.:Acidity and basicity.
  
presuppositions: Plasma is the same as ionized gas.
corrections: Plasma is not the same as ionized gas.
raw_presuppositions: Plasma is the same as ionized gas. Plasma is the same as ionized gas.
raw_corrections: Plasma is not the same as ionized gas. Plasma is not the same as ionized gas.