Definition of Plasma (State of Matter, Physics and Chemistry)

Angel Zamora Ramirez
Degree in physics

Plasma is a gaseous fluid in which a fraction of it is ionized, that is, it has a considerable amount of ions and free electrons, constituting the fourth state of aggregation of the subject.

Solid, liquid and gas... Perhaps most of us are familiar with these three states of the matter, however, there is a fourth state of aggregation that follows from the gaseous state and that we often pass through high. It is about plasma, an ionized gas that we can find in stars, plasma screens, fire, etc.

Plasma as a state of aggregation

When matter is in a solid state, its atoms or molecules are subject to cohesive forces between them and form defined structures. If we change the temperature or pressure of a solid in such a way that its molecules they start to move more, eventually the intermolecular forces decrease and we go to the state liquid.

In the liquid state the cohesive forces between molecules are less than in the solid state. Matter in a liquid state has a less organized structure and therefore does not have a defined volume. As in the previous case, if we modify the temperature or pressure of the liquid we can make it change to a gaseous state.

In a gas, the intermolecular forces are very small and in some cases practically zero. Gases are considered fluids in which the molecules that compose them move freely. By increasing the temperature or pressure of a gas, more movement of the molecules that compose it is generated and the number of collisions also increases. These collisions can cause the electrons of certain atoms to break free from their orbitals and go free.

It is at this point that a plasma is generated, an ionized gas with a certain amount of cations (positive ions) and free electrons. Free electrical charges make plasmas excellent electrical conductors and also respond to electromagnetic fields.

It could be said that this new state of matter was first studied by William Crookes in his experiments with cathode rays in the 1880s. However, it was the physicist Irving Langmuir who in 1928 coined the term "plasma" to refer to this ionized gas that would later be considered another state of matter.

Plasma on Earth and in the Universe

Plasma is considered the most abundant state of aggregation of matter. Almost 99% of the baryonic matter that we can observe in the Universe is in the plasmatic state.

This clearly does not apply to our planet, since most of the matter we observe here is in the other three states of aggregation. However, there are certain places or phenomena where we can observe matter in the plasmatic state. The lightning that we can observe during a thunderstorm results from the ionization of gas in the atmosphere. The ionosphere, which is the ionized layer of the atmosphere due to solar radiation, is also a plasma, as are the polar auroras that can be observed as a result of the interaction between the earth's magnetic field and the winds solar.

In the Universe we can find plasma almost everywhere. The stars themselves are large spheres of plasma resulting from thermonuclear reactions that occur in their cores. In addition, the heat generated by the stars also ionizes the gaseous medium that surrounds them, in general terms we can say that the interstellar medium is also a plasma. Also, stars tend to expel large jets of charged particles that we call "solar winds" and which are matter in the plasmatic state. Many of the nebulae that can be seen in various places in the Universe are nothing more than ionized gas that surrounds one or more stars.

In our day to day we can also find several examples of the technological use that plasma has. Plasma displays, as the name suggests, use compartments filled with noble gases that ionize and emit light. We can also find plasma in fluorescent tubes, neon lights, and plasma lamps that are used for decorative purposes.

A fifth state of matter?

Recent experiments carried out under extreme conditions have managed to obtain what many consider the fifth state of aggregation of matter. This is the Quark-Gluon Plasma, a type of plasma made up of free quarks and gluons.

Quarks and gluons are the building blocks of the protons and neutrons that make up atomic nuclei. Quark and gluon plasma is obtained in particle accelerators when heavy nuclei of lead or gold are collided. The collision between the nuclei generates enough temperature so that for a few moments the quarks and gluons are free and the plasma is formed.

Studying the plasma of quarks and gluons is especially relevant because during the first moments after the Big Bang and before the formation of the first atoms, it is believed that the existing matter was in this state.