State of Matter Definition

Chemistry Glossary Definition of State of Matter

Diagram of states of matter
The four most common states of matter are solid, liquid, gas, and plasma.

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Physics and chemistry both study matter, energy, and interactions between them. From the laws of thermodynamics, scientists know matter can change states and the sum of the matter and energy of a system is constant. When energy is added or removed to matter, it changes state to form a state of matter. A state of matter is defined as one of the ways in which matter can interact with itself to form a homogeneous phase.

State of Matter vs Phase of Matter

The phrases "state of matter" and "phase of matter" are used interchangeably. For the most part, this is fine. Technically a system can contain several phases of the same state of matter. For example, a bar of steel (a solid) may contain ferrite, cementite, and austenite. A mixture of oil and vinegar (a liquid) contains two separate liquid phases.

States of Matter

In everyday life, four phases of matter exist: solids, liquids, gases, and plasma. However, several other states of matter have been discovered. Some of these other states occur at the boundary between two states of matter where a substance doesn't really display the properties of either state. Others are most exotic. This is a list of some states of matter and their properties:

Solid: A solid has a defined shape and volume. Particles within a solid are packed very close together fixed in an ordered arrangement. The arrangement may be sufficiently ordered to form a crystal (e.g., NaCl or table salt crystal, quartz) or the arrangement may be disordered or amorphous (e.g., wax, cotton, window glass).

Liquid: A liquid has a defined volume but lacks a defined shape. Particles within a liquid are not packed as close together as in a solid, allowing them to slide against each other. Examples of liquids include water, oil, and alcohol.

Gas: A gas lacks either a defined shape or volume. Gas particles are widely separated. Examples of gases include air and the helium in a balloon.

Plasma: Like a gas, a plasma lacks a defined shape or volume. However, the particles of a plasma are electrically charged and are separated by vast differences. Examples of plasma include lightning and the aurora.

Glass: A glass is an amorphous solid intermediate between a crystalline lattice and a liquid. It is sometimes considered a separate state of matter because it has properties distinct from solids or liquids and because it exists in a metastable state.

Superfluid: A superfluid is a second liquid state that occurs near absolute zero. Unlike a normal liquid, a superfluid has zero viscosity.

Bose-Einstein Condensate: A Bose-Einstein condensate may be called the fifth state of matter. In a Bose-Einstein condensate the particles of matter stop behaving as individual entities and may be described with a single wavefunction.

Fermionic Condensate: Like a Bose-Einstein condensate, particles in a fermionic condensate may be described by one uniform wavefunction. The difference is the condensate is formed by fermions. Because of the Pauli exclusion principle, fermions can't share the same quantum state, but in this case pairs of fermions behave as bosons.

Dropleton: This is a "quantum fog" of electrons and holes that flow much like a liquid.

Degenerate Matter: Degenerate matter is actually a collection of exotic states of matter that occur under extremely high pressure (e.g., within the cores of stars or massive planets like Jupiter). The term "degenerate" derives from the way matter can exist in two states with the same energy, making them interchangeable.

Gravitational Singularity: A singularity, like at the center of a black hole, is not a state of matter. However, it bears noting because it's an "object" formed by mass and energy that lacks matter.

Phase Changes Between States of Matter

Matter can change states when energy is added or removed from the system. Usually, this energy results from changes in pressure or temperature. When matter changes states it undergoes a phase transition or phase change.

Sources

  • Goodstein, D. L. (1985). States of Matter. Dover Phoenix. ISBN 978-0-486-49506-4.
  • Murthy, G.; et al. (1997). "Superfluids and Supersolids on Frustrated Two-Dimensional Lattices". Physical Review B. 55 (5): 3104. doi:10.1103/PhysRevB.55.3104
  • Sutton, A. P. (1993). Electronic Structure of Materials. Oxford Science Publications. pp. 10–12. ISBN 978-0-19-851754-2.
  • Valigra, Lori (June 22, 2005) MIT Physicists Create New Form of Matter. MIT News.
  • Wahab, M.A. (2005). Solid State Physics: Structure and Properties of Materials. Alpha Science. pp. 1–3. ISBN 978-1-84265-218-3.