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A quark (/ k w ɔːr k, k w ɑːr k /) is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. [1] All commonly observable matter is composed of up quarks, down quarks and electrons.
Such states of matter are studied in condensed matter physics. In extreme conditions found in some stars and in the early universe, atoms break into their constituents and matter exists as some form of degenerate matter or quark matter. Such states of matter are studied in high-energy physics.
In bulk, matter can exist in several different forms, or states of aggregation, known as phases, [49] depending on ambient pressure, temperature and volume. [50] A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth).
The term phase is sometimes used as a synonym for state of matter, but it is possible for a single compound to form different phases that are in the same state of matter. For example, ice is the solid state of water, but there are multiple phases of ice with different crystal structures , which are formed at different pressures and temperatures.
For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons (hydrogen-1, by far the most common form, [57] also called protium), one neutron , two neutrons and more than two neutrons. The known elements form a set of atomic numbers, from the single-proton element hydrogen up to the 118-proton element oganesson ...
Chemistry is the scientific study of the properties and behavior of matter. [1] It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during reactions with other substances.
Water is a well-known example of such a material. For example, water ice is ordinarily found in the hexagonal form ice I h, but can also exist as the cubic ice I c, the rhombohedral ice II, and many other forms. Polymorphism is the ability of a solid to exist in more than one crystal form. For pure chemical elements, polymorphism is known as ...
Subatomic particles such as protons or neutrons, which contain two or more elementary particles, are known as composite particles. Ordinary matter is composed of atoms, themselves once thought to be indivisible elementary particles. The name atom comes from the Ancient Greek word ἄτομος which means indivisible or uncuttable.