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A type of subatomic particle consisting of two protons and two neutrons bound together into a particle identical to the nucleus of a helium-4 ion. It has a charge of +2 e and a mass of 4 u . Alpha particles are classically produced in the process of radioactive alpha decay , but may also be produced in other ways and given the same name.
A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...
Avogadro constant (N A) The ratio of the number of discrete constituent particles (such as molecules, atoms, or ions) to the amount of a substance, defined as exactly 6.022 140 76 × 10 23 mol −1. Avogadro number The number of discrete constituent particles in one mole of a substance, defined as exactly 6.02214076 × 10 23.
The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. Atoms of the same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules.
[3] [4] No writer before Rutherford is known to have used the term "atomic number" in this way, so it was probably he who established this definition. [ 5 ] [ 6 ] After Rutherford deduced the existence of the proton in 1920, "atomic number" customarily referred to the proton number of an atom.
In regular cold matter, quarks, fundamental particles of nuclear matter, are confined by the strong force into hadrons that consist of 2–4 quarks, such as protons and neutrons. Quark matter or quantum chromodynamical (QCD) matter is a group of phases where the strong force is overcome and quarks are deconfined and free to move.
A table or chart of nuclides is a two-dimensional graph of isotopes of the elements, in which one axis represents the number of neutrons (symbol N) and the other represents the number of protons (atomic number, symbol Z) in the atomic nucleus. Each point plotted on the graph thus represents a nuclide of a known or hypothetical chemical element.
An example is calcium-40, with 20 neutrons and 20 protons, which is the heaviest stable isotope made of the same number of protons and neutrons. Both calcium-48 and nickel-48 are doubly magic because calcium-48 has 20 protons and 28 neutrons while nickel-48 has 28 protons and 20 neutrons. Calcium-48 is very neutron-rich for such a relatively ...