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electron

Electron

Stan Zurek, Electron, Encyclopedia-Magnetica.com, {accessed 2021-03-08}
…this pages is being edited…
Electron - elementary particle
Electric charge:1)
-1.602 176 634 × 10-19 C
Mass:2)
9.109 383 7015 × 10-31 kg
Magnetic moment:3)
-9.284 764 7043 × 10-24 J/T
-1.001 159 652 181 28 μB
Spin: ½
Antiparticle: positron

Electron (typically denoted by a symbol e) - a fundamental sub-atomic particle which has the intrinsic property of a negative elementary electric charge.4)

An electron is a part of every atom, with the number of electrons corresponding to the number of protons (atomic number), so that their electrical charges balance out and an atom can be electrically neutral.5)

Electron's mass is only around 1/1836 of proton's, despite both having equal but opposite electric charge.6) For this reason, electrons contribute to less than 0.1% of the mass of atoms.

Prof. Frank Wilczek:7)
So, what is an electron? An electron is a particle and a wave; it is ideally simple and unimaginably complex; it is precisely understood and utterly mysterious; it is rigid and subject to creative disassembly. No single answer does justice to reality.

The small size of electrons allows obtaining much finer resolution of an electron microscope than it is possible for an optical microscope.

Electric and magnetic properties of electrons, as well as their electromagnetic interactions dictate many properties of matter, obviously electrical, electronic and magnetic, but also chemical properties.

The name “electron” was proposed by G.J. Stone in 1894, and the electron was discovered by J.J. Thompson in 1897. Electron's mass and charge were measured by R.A. Millikan and H. Fletcher in 1909.8)


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This page is being edited and can be incomplete or incorrect.

Microscopic properties

Microscopic properties of an electron have been extensively studied since its discovery. However, because of its very small size there are no experimental techniques which allow direct “probing” or visualising in the same sense as it is possible to observe some small structures under an optical microscope.9)

Many properties of electron, such as electric charge or spin are detectable or measurable. It is possible to describe the rules of but it is not possible to explain the reason for their existence, and therefore they are asummed to be “fundamental” properties.

Size

Electron size
Karim (2020)10) ~1 × 10-36 m
Mac Gregor (1992)11) < 1 × 10-18 m
Dhobi et al. (2020)12) 1 × 10-15 m
Mac Gregor (1992)13) 5 × 10-13 m
Wilczek (2013)14) 2 × 10-12 m
Dhobi et al. (2020)15) 2 × 10-12 m

Size of a particle has meaning in classical physics. However, at very small scales the quantum effects begin to play a significant role and it difficult to define the meaning of “size” of the assumed spherical object. It is not straightforward to agree even on methodology which should be used for definition, calculation or measurement.16)17) Measurement at decreasing scales require larger energies, which can produce additional particles and thus confuse the outcome of the measurement.

Wilczek (2013):18)
Attempts to pin down an electron's position more accurately than this require, according to the uncertainty principle, injecting the electron with so much energy that extra electrons and anti-electrons are produced, confusing the identity of the original electron.

Depending on the approach there can be several radius definitions for the electron:19)

  • classical electron radius
  • quantum-mechanical Compton radius
  • QED-corrected quantum-mechanical Compton radius
  • electric charge radius
  • observed QED charge distribution for a bound electron
  • magnetic field radius

By using known physical constants and experimental data, the calculations based on these different approaches can give estimates which differ by several orders of magnitude.20)21)22)

Consequently, the question “What is the size of the electron?” remains one of the unanswered questions in physics.23)

Electric charge

See also the main article: Electric charge.
Schematic representation of electrostatic field of a stationary negative charge, by using electric field lines

S. Zurek, Encyclopedia Magnetica, CC-BY-4.0

Scientists can describe, but still cannot explain what exactly is electric charge. However, it is sufficient for such a basic property that it exists, it has some physical meaning and is measurable within the given system of units.24)

An electron possesses an elementary amount of negative electric charge e. Its value is a physical constant, expressed in the SI system as: -1 e = -1.602 176 634 × 10-19 C, and electric charge of other bodies can be expressed as integer multiples of it.25)

Only such sub-atomic particles like quarks are thought to have electric electric charge in non-integer quantities e.g. -1/3 e or +2/3 e, but they only exists in configurations which add up to integer values of charge. For example, proton comprises three quarks (up, up, down), which add up to +1 e. Therefore, in any macroscopic application there the charge is always quantised by the elementary amount of 1 e.26)27)

An electron in isolation is an electric monopole - it is a source of electric field. By convention, it is assumed that that imaginary electric field lines begin at positive charges and terminate at negative charges.28)

Like charges repel, opposite charges attract, causing mechanical forces which act on the charged bodies. This can be referred to as the electrostatic force, because it exists always, even if the charges remain stationary. This is different from magnetic or electromagnetic forces, which arise when the electric charges are in motion.

A neutral body can become polarised in electric field, by means of electrostatic induction, without the need for the charges to exchange between the bodies.

Opposite charges attract, same charges repel, neutral bodies generate no force (grey) but neutral bodies in the presence of other charges become locally polarised due to electrostatic induction

S. Zurek, Encyclopedia Magnetica, CC-BY-4.0

Spin

Electron spin as an analogy of a sphere spinning around its own axis29)

S. Zurek, Encyclopedia Magnetica, CC-BY-4.0

An electron possesses a fundamental property called spin, and an angular momentum as well as magnetic moment associated with it. Both of these values are physical constants.30)

Spin is a quantum property and does not have a direct equivalent in classical physics. However, because of the difficulty of the concept, an analogy is typically used, in which an electron is portrayed as a spinning sphere.

Electron's angular momentum is h/4π = 5.27 × 10-35 J/Hz, where h is the Planck’s constant.31)

Orbital magnetic moment

Magnetic moment of an electric current flowing in a loop can be expressed as the product of the amplitude of the current and the area of the loop.

The analogy of orbital moment is an electron orbiting the nucleus on a circular orbit (left) and for spin the sphere spins around its own axis (right)

S. Zurek, Encyclopedia Magnetica, CC-BY-4.0

An electron orbiting around the nucleus represents a moving electric charge which is equivalent to electric current. Therefore, in from the classical physics viewpoint there will be a magnetic moment associated with the orbital motion of an electron, in a loop without resistance.32)

Spin magnetic moment

Atomic orbitals

Demonstration of standing waves on vibrating circular plate, with radial nodes (circles) at lower frequencies, and angular modes (with “spokes”) at higher frequencies CNX_Chem_06_01_ Frequency by P. Flowers, W.R. Robinson, R. Langley, K. Theopold, OpenStax.org, CC-BY-4.0
Diagram of electron structure in an atom: shells, subshells and orbitals, with example for iron

S. Zurek, Encyclopedia Magnetica, CC-BY-4.0

Chemical properties

Antimatter

Macroscopic phenomena

Behaviour of electrons in materials defines their electric and magnetic properties.

Electricity

Insulators

Semiconductors

Conductors

Superconductors

Magnetism

Magnetic field

Magnetic properties

See also

References

electron.txt · Last modified: 2021/03/08 01:01 by stan_zurek

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