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element, chemical

A substance that cannot be decomposed into more elementary constituent substances by the methods of chemistry. From a physics point of view, to every chemical element corresponds a specific atom which is defined uniquely by the number of protons in its atomic nucleus (for example: nuclei with a single proton define the element hydrogen, two protons define helium, three Lithium, 26 iron and 92 uranium).

Definitioner

Lithium

Chemisches Element, dessen Atomkerne je drei Protonen enthalten. Im Rahmen der Allgemeinen Relativitätstheorie interessant, weil die Urknallmodelle Vorhersagen darüber machen, wieviel Kerne dieses und anderer leichter Elemente sich im frühen Universum gebildet haben sollten.

proton

Particle that carries positive electric charge and is comparatively massive; the atomic nuclei consist of protons and neutrons. Protons are not elementary particles, they are compound particles consisting of quarks that are bound together through the strong nuclear interaction . Collectively, protons, neutrons and a number of similar particles are called baryons.

protons (proton)

point

Elementary "building block" of geometrical entities such as surfaces or more general spaces. For instance, a surface is the set of all its points, of all possible locations on the surface, and all geometrical objects in that surface are defined by the points that belong to them - for instance, a line on the surface is the set of (infinitely many) points.

nuclei (nucleus)

Extremely dense central region of an atom, consisting of protons and neutrons held together by nuclear forces. The number of protons determines what chemical element a nucleus represents. Typical diameter for atomic nuclei are in the region of a quadrillionth of a metre= 10^-15 metres. This makes nuclei about a hundredth of a thousandth as large as atoms.

hydrogen

The lightest (and, in our universe, the most abundant) chemical element. The atomic nucleus of an ordinary hydrogen atom is a single proton. If the atomic nucleus contains an additional neutron, the atom is called heavy hydrogen or deuterium.

helium

After hydrogen, the second lightest chemical element. Its atomic nucleus consists of two protons and, ordinarily, two neutrons ("helium-4"); such helium nuclei are also called alpha particles. Another variety of helium, helium-3, has only one neutron in its nucleus. In the context of general relativity, both helium-3 and helium-4 are is of interest as two species of light atomic nuclei that formed in the early universe during Big Bang Nucleosynthesis.

chemical element (element, chemical)

chemical element

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element, chemical

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