States of matter are forms in which matter exists. The four states of matter observed in everyday life are solids, liquids, gases, and plasma. Other states of matter also exist, although they require special conditions. Here is a look at the states of matter, their properties, and the names of phase transitions between them.
Matter is anything that has mass and takes up space. It consists of subatomic particles, atoms, ions, and compounds. Sometimes these particles are tightly bound and close together, while other times particles are loosely connected and widely separated. States of matter describe the qualities displayed by matter. Basically, the state of matter of a substance depends on how much energy its particles have.
We can change the energy of matter by altering its temperature or pressure, causing matter to transition from one state to another. But, when matter changes state, its chemical identity remains the same. So, if you take ice, melt it, and then boil it, its state of matter changes, but it’s always water.
The four fundamental states of matter are solids, liquids, gases, and plasma. But, scientists are discovering new states of matter that exist under extreme conditions.
A solid is a state of matter with a defined shape and volume. Atoms, ions, and molecules in a solid pack tightly together and may form crystals. Examples of solids include rocks, ice, diamond, and wood.
A liquid is a state of matter with a defined volume, but no defined shape. In other words, liquids take the shape of their container. Particles in a liquid have more energy than in a solid, so they are further apart and less organized (more random). Examples of liquids include water, juice, and vegetable oil.
A gas is a state of matter lacking either a defined volume or defined shape. Like a liquid, a gas takes the shape of a container. Unlike a liquid, a gas easily expands or contracts to fill the entire volume of the container. Particles in a gas have more energy than in solids or liquids. They tend to be further apart and move more randomly than in a liquid. Examples of gases include air, water vapor, and helium.
Plasma is a state of matter similar to a gas, except all of the particles carry an electrical charge. Also, plasma tends to exist at very low pressure, so the particles are even further apart than in a gas. Plasma can consist of ions, electrons, or protons. Examples of plasma include lightning, the aurora, the Sun, and the inside of a neon sign.
Bose-Einstein condensate (BEC) is sometimes called the fifth state of matter. In Bose-Einstein condensate, atoms and ions stop behaving as separate particles and collapse into a single quantum state that can be described using a single wavefunction. This state of matter was verified experimentally in 1995 by Eric Cornell and Carl Wieman. Bose-Einstein condensate is “colder” than an ordinary solid and may form very near absolute zero.
A superfluid is a second liquid state formed by some types of matter. A superfluid displays zero viscosity. In other words, it has no resistance to flow. Superfluidity was observed for helium in 1937. Because it could flow without friction, superfluid helium climbed the walls of its container and dripped over the sides. Like Bose-Einstein condensate, superfluidity occurs near absolute zero.
A fermionic condensate is a state of matter similar to a Bose-Einstein condensate, except it consists of fermions, such as quarks and leptons. Normally, the Pauli exclusion principle forbids fermions from entering the same quantum state. In a fermionic condensate, a pair of fermions behaves as a boson, allowing multiple pairs to enter the same quantum state.
Rydberg matter is a type of plasma formed when excited ions condense. You can think of it as dusty plasma. So far, it occurs in the elements hydrogen, potassium, nitrogen, and cesium. This type of matter consists mainly of small hexagonal planar clusters. Scientists make Rydberg matter in a lab or observe it in the upper atmosphere of planets and in clouds in space.
Photonic matter is the state of matter formed when photons interact with a gas in such a way that the photons have apparent mass and can interact with each other. Photons with apparent mass can even form photonic “molecules.”
Color-glass condensate is a state of matter proposed to exist when atomic nuclei travel near the speed of liquid. Because of their speed, the nucleus appears compressed along its direction of motion. This causes the gluons of the nucleus to appear as a sort of wall or region of increased density.
There are other proposed states of matter, including quark matter, degenerate matter, dropleton, quantum Hall state, superglass, supersolid, and string-net liquid.
Changes in temperature and pressure causes matter to change from one state to another. This change is called a phase transition or phase change. Examples of phase transitions including the melting of ice (a solid) into water (a liquid) and the boiling of water into water vapor (a gas). Here are the names of the phase transitions between solids, liquids, gases, and plasma:
