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In particle physics, the electron mass (symbol: m e) is the mass of a stationary electron, also known as the invariant mass of the electron. It is one of the fundamental constants of physics . It has a value of about 9.109 × 10 −31 kilograms or about 5.486 × 10 −4 daltons , which has an energy-equivalent of about 8.187 × 10 −14 joules ...
The electron's mass is approximately 1 / 1836 that of the proton. [15] Quantum mechanical properties of the electron include an intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, per the Pauli exclusion principle. [14]
The relative isotopic mass, then, is the mass of a given isotope (specifically, any single nuclide), when this value is scaled by the mass of carbon-12, where the latter has to be determined experimentally. Equivalently, the relative isotopic mass of an isotope or nuclide is the mass of the isotope relative to 1/12 of the mass of a carbon-12 atom.
A set of base units in the atomic system as in one proposal are the electron rest mass, the magnitude of the electronic charge, the Planck constant, and the permittivity. [6] [9] In the atomic units system, each of these takes the value 1; the corresponding values in the International System of Units [10]: 132 are given in the table.
where is the elementary charge, is the electron mass, is the speed of light, and is the permittivity of free space. [1] This numerical value is several times larger than the radius of the proton . In cgs units , the permittivity factor and 1 4 π {\displaystyle {\frac {1}{4\pi }}} do not enter, but the classical electron radius has the same value.
The elementary charge, usually denoted by e, is a fundamental physical constant, defined as the electric charge carried by a single proton (+1 e) or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 e.
The masses of those particles are small compared to nucleons—the mass of an electron (0.511 MeV/c 2) [18] and the mass of a muon (with a value of 105.7 MeV/c 2) [19] are fractions of the mass of the "heavy" proton (938.3 MeV/c 2), and the mass of a neutrino is nearly zero. [20]
In general, however, the value of effective mass depends on the purpose for which it is used, and can vary depending on a number of factors. For electrons or electron holes in a solid, the effective mass is usually stated as a factor multiplying the rest mass of an electron, m e (9.11 × 10 −31 kg).