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Plasma: the negatively charged electrons (yellow) are freely streaming through the positively charged ions (blue).
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The Plasma State

Plasma is known as the fourth state of matter. The other three states are solid, liquid and gas.

In most cases, matter on Earth has electrons that orbit around the atom's nucleus. The negatively charged electrons are attracted to the positively charged nucleus. Remember, opposites attract! So the electrons stay in orbit around the nucleus. When temperatures get REALLY hot, the electrons can escape out of their orbit around the atom's nucleus. When the electron(s) leave, that leaves behind what scientists call a positively charged ion. This whole process is similar to a spacecraft that escapes the Earth's gravitational pull.

In summary, when electrons are no longer trapped in orbits around the nucleus, we have the plasma state. This is when a gas becomes a bunch of electrons which have escaped the pull of the nucleus and ions which are positively charged because they have lost one or more electrons.

Most of the matter in the universe is found in the plasma state. That is because stars contain so much of the matter in the universe (stars are so hot that their matter can only exist in the plasma state).

Last modified January 22, 2001 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA