![]() ![]() Water can be said to have several distinct solid states. A distinct state of matter can be defined as any set of states distinguished from any other set of states by a phase transition. A phase transition indicates a change in structure and can be recognized by an abrupt change in properties. This diagram illustrates transitions between the four fundamental states of matter.Ī state of matter is also characterized by phase transitions. At very high temperatures, such as those present in stars, it is assumed that essentially all electrons are “free”, and that a very high-energy plasma is essentially bare nuclei swimming in a sea of electrons. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons. Lightning, electric sparks, fluorescent lights, neon lights, plasma televisions, some types of flame and the stars are all examples of illuminated matter in the plasma state.Ī gas is usually converted to a plasma in one of two ways, either from a huge voltage difference between two points, or by exposing it to extremely high temperatures. The plasma state is often misunderstood, but it is actually quite common on Earth, and the majority of people observe it on a regular basis without even realizing it. In fact it is this electron “sea” that allows matter in the plasma state to conduct electricity. Positively charged nuclei swim in a “sea” of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal. ![]() Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Like a gas, plasma does not have definite shape or volume. For example, supercritical carbon dioxide is used to extract caffeine in the manufacture of decaffeinated coffee. A supercritical fluid has the physical properties of a gas, but its high density confers solvent properties in some cases, which leads to useful applications. In this state, the distinction between liquid and gas disappears. A vapour can exist in equilibrium with a liquid (or solid), in which case the gas pressure equals the vapor pressure of the liquid (or solid).Ī supercritical fluid (SCF) is a gas whose temperature and pressure are above the critical temperature and critical pressure respectively. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature.Īt temperatures below its critical temperature, a gas is also called a vapor, and can be liquefied by compression alone without cooling. A gas has no definite shape or volume, but occupies the entire container in which it is confined. In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighboring molecules is much greater than the molecular size. Not only will a gas conform to the shape of its container but it will also expand to fill the container. Solids can be transformed into liquids by melting and can also change directly into gases through the process of sublimation. Glasses and other non-crystalline, amorphous solids without long-range order are not thermal equilibrium ground states therefore they are described below as nonclassical states of matter. Ice has fifteen known crystal structures, or fifteen solid phases, which exist at various temperatures and pressures. For example, iron has a body-centred cubic structure at temperatures below 912 ☌, and a face-centred cubic structure between 9 ☌. There are various different crystal structures, and the same substance can have more than one structure (or solid phase). In crystalline solids, the particles (atoms, molecules, or ions) are packed in a regularly ordered, repeating pattern. Solids can only change their shape by force, as when broken or cut. As a result, a solid has a stable, definite shape, and a definite volume. The forces between particles are strong so that the particles cannot move freely but can only vibrate. In a solid, the particles (ions, atoms or molecules) are closely packed together. Clockwise from top left, they are solid, liquid, plasma and gas, represented by an ice sculpture, a drop of water, electrical arcing from a tesla coil, and the air around clouds respectively. ![]()
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