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Liquids and Solids



A liquid is a phase of matter with definite volume but no definite shape. Liquids are subject to cohesive forces, which attract like molecules, and adhesive forces, which attract unlike molecules. A solid is a phase of matter with definite shape and volume. Solids may be amorphous, in which there is no regular, repeating pattern, or crystalline, in which particles are arranged in a regular, repeating pattern. Crystalline solids may be metallic, ionic, covalent, or molecular solids. Crystalline solids can be described by their unit cells, the smallest repeating units of matter within them. The attributes of a unit cell for a substance can be determined by X-ray crystallography, a method in which X-rays are diffracted by particles in a crystal and the diffracted beams are absorbed and studied. Matter is affected by its internal energy and adopts forms ranging from solids, liquids, gases, and plasmas (four common states of matter) through several phase transitions, which include freezing, melting, vaporization, condensation, sublimation, and deposition. Changes between these states of matter can be graphed on a phase diagram.

At A Glance

  • Liquids are a type of matter with definite volume but no definite shape. Particles of a liquid experience cohesive forces, which give rise to surface tension, and adhesive forces, which give rise to capillary action.
  • Solids have a definite shape and volume. They can be amorphous, with no regular pattern among the particles, or crystalline, in which the particles repeat at regular intervals within a crystalline lattice.
  • Crystalline solids can be described by the type of repeating units, called unit cells, of which they consist.
  • X-ray crystallography, a method of determining the molecular structure of a crystal by diffracting light through it, gives information about the makeup of a crystal's unit cell.
  • Solid, liquid, and gas are three common states of matter on Earth. A change between these phases is a phase transition. A fourth state of matter, plasma, is less common on Earth because it requires high energies.
  • A phase diagram is a graphical representation of the relationship between a substance's phases of matter and temperature, as well as pressure.