Plasma is the state of matter that consists of a mass of free electrons and positively charged particles called “cations” mixed together.
Plasma has neither a specific shape nor a consistent volume. In other words, plasma can easily flow into and take the shape of a container, and will expand, redistributing itself to evenly fill that container.
Although the properties of plasma are similar to those of gases, plasma and gases are not the same thing. In plasma, electrons are released from their orbits around a nucleus, creating a “soup” of free electrons and nuclei. Because these charged particles are loose, plasma easily conducts electricity, and both produces and responds to magnetic fields.
Plasma is created when a gas is either exposed to a high temperature, or when high voltage electricity is passed through it. The heat or electricity makes the atoms in the gas move so quickly and collide so violently with one another that electrons are knocked from their orbits. Because of the way they are created, plasmas are sometimes called “ionized gases.”
Although plasma isn’t discussed as often as solids, liquids, and gases, and was the last phase of matter discovered, you’re probably more familiar with plasma than you think. Plasma gives neon and fluorescent lights their glow, is formed during lightning strikes, and, of course, is present in plasma televisions. Chemists also classify fire as a plasma.
Plasma makes up our sun, and is visible in the solar flares that erupt from its surface. Because plasma is the “stuff of stars,” it is the most common state of matter, making up about 99% of the observable universe.