Learn About Electrons

In this episode of the I Can't Sleep Podcast, fall asleep learning about Electrons. Isn't science cool? Yes, it is. And, the combo of learning about our universe from a Wikipedia perspective does the job of helping you get the sleep you deserve tonight. Happy sleeping!

Transcript

Welcome to the I Can't Sleep podcast,

Where I read random articles from across the web to bore you to sleep with my soothing voice.

I'm your host,

Benjamin Boster.

Today's episode is from a Wikipedia article titled,

Electron.

The electron is a subatomic particle with a negative one elementary electric charge.

Electrons belong to the first generation of the leptin particle family,

And are generally thought to be elementary particles because they have no known components or substructure.

Electron's mass is approximately 1 over 1836 that of the proton.

Quantum mechanical properties of the electron include an intrinsic angular momentum,

Spin of a half-integer value,

Expressed in the units of the reduced Planck constant h-bar.

Being fermions,

No two electrons can occupy the same quantum state,

Per the Pauli exclusion principle.

Like all elementary particles,

Electrons exhibit properties of both particles and waves.

They can collide with other particles,

And can be diffracted like light.

The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons,

Because electrons have a lower mass,

And hence a longer de Broglie wavelength for a given energy.

Electrons play an essential role in numerous physical phenomena,

Such as electricity,

Magnetism,

Chemistry,

And thermal conductivity.

They also participate in gravitational,

Electromagnetic,

And weak interactions.

Since an electron has charge,

It has a surrounding electric field.

If that electron is moving relative to an observer,

The observer will observe it to generate a magnetic field.

Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law.

Electrons radiate or absorb energy in the form of photons when they are accelerated.

Laboratory instruments are capable of trapping individual electrons,

As well as electron plasma,

By the use of electromagnetic fields.

Digital telescopes can detect electron plasma in outer space.

Electrons are involved in many applications,

Such as tribiology,

Or frictional charging,

Electrolysis,

Electrochemistry,

Battery technologies,

Electronics,

Welding,

Cathode ray tubes,

Photoelectricity,

Photovoltaic solar panels,

Electron microscopes,

Radiation therapy,

Lasers,

Gaseous ionization detectors,

And particle accelerators.

Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics.

The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without allows the composition of the two known as atoms.

Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system.

The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.

In 1838,

British natural philosopher Richard Leaming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms.

Irish physicist George Johnstone Stoney named this charge electron in 1891,

And J.

J.

Thompson and his team of British physicists identified it as a particle in 1897 during the cathode ray tube experiment.

Electrons participate in nuclear reactions,

Such as nucleosynthesis in stars,

Where they are known as beta particles.

Electrons can be created through beta decay of radioactive isotopes and in high energy collisions,

For instance,

When cosmic rays enter the atmosphere.

The antiparticle of the electron is called the positron.

It is identical to the electron except that it carries electrical charge of the opposite sign.

When an electron collides with a positron,

Both particles can be annihilated,

Producing gamma ray photons.

The ancient Greeks noticed that amber attracted small objects when rubbed with fur.

Along with lightning,

This phenomenon is one of humanity's earliest recorded experiences with electricity.

In his 1600 treatise De Magnete,

The English scientist William Gilbert coined the Neo-Latin term electrica to refer to those substances with property similar to that of amber which attracts small objects after being rubbed.

Both electric and electricity are derived from the Latin electrum,

Also the root of the alloy of the same name,

Which came from the Greek word for amber,

Electron.

In the early 1700s,

French chemist Charles-Francois Dufay found that if a charged gold leaf is repulsed by glass rubbed with silk,

Then the same charged gold leaf is attracted by amber rubbed with wool.

From this and other results of similar types of experiments,

Dufay concluded that electricity consists of two electrical fluids,

Vitreous fluid from glass rubbed with silk and resinous fluid from amber rubbed with wool.

These two fluids can neutralize each other when combined.

American scientist Ebenezer Kinnersley later also independently reached the same conclusion.

A decade later,

Benjamin Franklin proposed that electricity was not from different types of electrical fluid,

But a single electrical fluid showing an excess,

Positive,

Or deficit,

Negative.

He gave them the modern charge nomenclature of positive and negative,

Respectively.

Franklin thought of the charge carrier as being positive,

But he did not correctly identify which situation was a surplus of the charge carrier and which situation was a deficit.

Between 1838 and 1851,

British national philosopher Richard Lehmann developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges.

Beginning in 1846,

German physicist Wilhelm Eduard Weber theorized that electricity was composed of positively and negatively charged fluids,

And their interaction was governed by the inverse square law.

After studying the phenomenon of electrolysis in 1874,

Irish physicist George John Stone Stoney suggested that there existed a single definite quantity of electricity,

The charge of a monovalent ion.

He was able to estimate the value of this elementary charge E by means of Faraday's law of electrolysis.

However,

Stoney believed these charges were permanently attached to atoms and could not be removed.

In 1881,

German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts,

Each of which behaves like atoms of electricity.

Stoney initially coined the term electrolyon in 1881.

Ten years later,

He switched to electron to describe these elementary charges,

Writing in 1894,

An estimate was made of the actual amount of this most remarkable fundamental unit of electricity,

For which I have since ventured to suggest the name electron.

A 1906 proposal to change the electrion failed because Hendrik Lorentz preferred to keep electron.

The word electron is a combination of the words electric and ion.

The suffix on,

Which is now used to designate other subatomic particles,

Such as a proton or neutron,

Is in turn derived from electron.

While studying electrical conductivity in rare field gases in 1859,

The German physicist Julius Plüker observed the radiation emitted from the cathode caused phosphorescent light to appear on the tube wall near the cathode,

And the region of the phosphorescent light could be moved by application of a magnetic field.

In 1869,

Plüker's student Johann Wilhelm Hiddorf found that a solid body placed in between the cathode and the phosphorescence would cast a shadow upon the phosphorescent region of the tube.

Hiddorf inferred that there are straight rays emitted from the cathode and that the phosphorescence was caused by the rays striking the tube walls.

In 1876,

The German physicist Eugene Goldstein showed that the rays were emitted perpendicular to the cathode surface,

Which distinguished between the rays that were emitted from the cathode and the incandescent light.

Goldstein dubbed the rays cathode rays.

Decades of experimental and theoretical research involving cathode rays were important in J.

J.

Thompson's eventual discovery of electrons.

During the 1870s,

The English chemist and physicist Sir William Crookes developed the first cathode ray tube to have a high vacuum inside.

He then showed in 1874 that the cathode rays can turn a small paddle wheel when placed in their path.

Therefore,

He concluded that the rays carried momentum.

Furthermore,

By applying a magnetic field,

He was able to deflect the rays,

Thereby demonstrating that the beam behaved as though it were negatively charged.

In 1879,

He proposed that these properties could be explained by regarding cathode rays as composed of negatively charged gaseous molecules in a fourth state of matter,

In which the mean free path of the particles is so long that collisions may be ignored.

The German-born British physicist Arthur Schuster expanded upon Crookes' experiments by placing metal plates parallel to the cathode rays and applying an electric potential between the plates.

The field deflected the rays toward the positively charged plate,

Providing further evidence that the rays carried negative charge.

By measuring the amount of deflection for a given electric and magnetic field,

In 1890 Schuster was able to estimate the charge-to-mass ratio of the ray components.

However,

This produced a value that was more than 1,

000 times greater than what was expected,

Although little credence was given to its calculations at the time.

This is because it was assumed that the charge carriers were much heavier hydrogen or nitrogen atoms.

Schuster's estimates would subsequently turn out to be largely correct.

In 1892,

Hendrik Lorentz suggested that the mass of these particles,

Electrons,

Could be a consequence of their electric charge.

While studying naturally fluorescing minerals in 1896,

The French physicist Henri Bacquerel discovered that they emitted radiation without any exposure to an external energy source.

These radioactive materials became the subject of much interest by scientists,

Including the New Zealand physicist Ernest Rutherford,

Who discovered they emitted particles.

He designated these particles alpha and beta on the basis of their ability to penetrate matter.

In 1900,

Bacquerel showed that the beta rays emitted by radium could be deflected by an electric field,

And that their mass-to-charge ratio was the same as for cathode rays.

This evidence strengthened the view that electrons existed as components of atoms.

In 1897,

The British physicist J.

J.

Thomson,

With his colleagues John S.

Townsend and H.

A.

Wilson,

Performed experiments indicating that cathode rays really were unique particles rather than waves,

Atoms,

Or molecules,

As was believed earlier.

Thomson made good estimates of both the charge E and the mass M,

Finding that cathode ray particles,

Which he called corpuscles,

Had perhaps one thousandth of the mass of the least massive ion known,

Hydrogen.

He showed that their charge-to-mass ratio,

E over M,

Was independent of cathode material.

He further showed that the negatively charged particles produced by radioactive materials,

By heated materials,

And by illuminated materials,

Were universal.

The name electron was adopted for these particles by the scientific community,

Mainly due to the advocation by G.

F.

Fitzgerald,

J.

Larmor,

And H.

A.

Lawrence.

In the same year,

Emil Wiechert and Walter Kaufmann also calculated the E over M ratio,

But they failed short of interpreting their results,

While J.

J.

Thomson would subsequently in 1899 give estimates for the electron charge and mass as well.

E is roughly 6.

8 x 10-10 ESU,

And M is roughly 3 x 10-6 grams.

The electron's charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil drop experiment of 1909,

The results of which were published in 1911.

This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity.

This device could measure the electric charge from as few as 1 to 150 ions,

With an error margin of less than 0.

3%.

Comparable experiments had been done earlier by Thomson's team,

Using clouds of charged water droplets generated by electrolysis,

And in 1911 by Abram Mayov,

Who independently obtained the same results as Millikan,

Using charged microparticles of metals,

Then published his results in 1913.

However,

Oil drops were more stable than water drops because of their slower evaporation rate,

And thus more suited to precise experimentation over long periods of time.

Around the beginning of the 20th century,

It was found that under certain conditions,

A fast-moving charged particle caused a condensation of supersaturated water vapor along its path.

In 1911,

Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles,

Such as fast-moving electrons.

By 1914,

Experiments by physicists Ernest Rutherford,

Henry Moseley,

James Franck,

And Gustav Hertz had largely established the structure of an atom as a dense nucleus of positive charge,

Surrounded by lower-mass electrons.

In 1913,

Danish physicist Niels Bohr postulated that electrons resided in quantized energy states,

With their energies determined by the angular momentum of the electron's orbit about the nucleus.

Electrons could move between those states,

Or orbits,

By the emission of absorption of photons of specific frequencies.

By means of these quantized orbits,

He accurately explained the spectral lines of the hydrogen atom.

However,

Bohr's model failed to account for the relative intensities of the spectral lines,

And it was unsuccessful in explaining the spectra of more complex atoms.

Chemical bonds between atoms were explained by Gilbert Newton Lewis,

Who in 1916 proposed that a covalent bond between two atoms is maintained by a pair of electrons shared between them.

Later in 1927,

Walter Heitler and Fritz Lundin gave the full explanation of the electron-pair formation and chemical bonding in terms of quantum mechanics.

In 1919,

The American chemist Irving Langmuir elaborated on the Lewis's static model of the atom,

And suggested that all electrons were distributed in successive concentric nearly spherical shells,

All of equal thickness.

In turn,

He divided the shells into a number of cells,

Each of which contained one pair of electrons.

With this model,

Langmuir was able to qualitatively explain the chemical properties of all elements in the periodic table,

Which were known to largely repeat themselves according to the periodic law.

In 1924,

Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state,

As long as each state was occupied by no more than a single electron.

This prohibition against more than one electron occupying the same quantum energy state became known as the Pauli Exclusion Principle.

The physical mechanism to explain the fourth parameter,

Which had two distinct possible values,

Was provided by the Dutch physicists Samuel Goudsmit and George Uhlenbeck.

In 1925,

They suggested that an electron,

In addition to the angular momentum of its orbit,

Possesses an intrinsic angular momentum and magnetic dipole moment.

This is analogous to the rotation of the earth on its axis as it orbits the sun.

The intrinsic angular momentum became known as spin,

And explained the previously mysterious splitting of spectral lines observed with a high-resolution spectrograph.

This phenomenon is known as fine-structure splitting.

In his 1924 dissertation,

Research on Quantum Theory,

French physicist Louis de Broglie hypothesized that all matter can be represented as a de Broglie wave in the manner of light.

That is,

Under the appropriate conditions,

Electrons and other matter would show properties of either particles or waves.

The corpuscular properties of a particle are demonstrated when it shows to have a localized position in space along its trajectory at any given moment.

The wave-like nature of light is displayed,

For example,

When a beam of light is passed through parallel slits,

Thereby creating interference patterns.

In 1927,

George Paget Thompson and Alexander Reed discovered the interference effect was produced when a beam of electrons was passed through thin celluloid foils,

And later metal films,

And by American physicists Clinton Davison and Lester Germer,

By the reflection of electrons from a crystal of nickel.

Alexander Reed,

Who was Thompson's graduate student,

Performed the first experiments,

But he died soon after in a motorcycle accident,

And is rarely mentioned.

De Broglie's prediction of a wave nature for electrons led Erwin Schrödinger to postulate a wave equation for electrons moving under the influence of the nucleus in the atom.

In 1926,

This equation,

The Schrödinger equation,

Successfully described how electron waves propagated.

Rather than yielding a solution that determined the location of an electron over time,

This wave equation also could be used to predict the probability of finding an electron near a position,

Especially a position near where the electron was bound in space,

For which the electron wave equation did not change in time.

This approach led to a second formulation of quantum mechanics,

And solutions of Schrödinger's equation,

Like Heisenberg's,

Provided derivations of the energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in 1913,

And that were known to reproduce the hydrogen spectrum.

Once spin and the interaction between multiple electrons were describable,

Quantum mechanics made it possible to predict the configuration of electrons in atoms with atomic numbers greater than hydrogen.

In 1928,

Building on Wolfgang Pauli's work,

Paul Dirac produced a model of the electron,

The Dirac equation,

Consistent with relativity theory by applying relativistic and symmetry considerations to the Hamiltonian formulation of the quantum mechanics of the electromagnetic field.

In order to resolve some problems within his relativistic equation,

Dirac developed in 1930 a model of the vacuum as an infinite sea of particles with negative energy,

Later dubbed the Dirac sea.

This led him to predict the existence of a positron,

The antimatter counterpart of the electron.

This particle was discovered in 1932 by Karl Andersen,

Who proposed calling standard electrons negatrons and using electron as a generic term to describe both the positively and negatively charged variants.

In 1947,

Willis Lamb,

Working in collaboration with graduate student Robert Rutherford,

Found that certain quantum states of the hydrogen atom,

Which should have the same energy,

Were shifted in relation to each other.

The difference came to be called the Lamb shift.

About the same time,

Polycarp Cush,

Working with Henry M.

Foley,

Discovered the magnetic moment of the electron is slightly larger than predicted by Dirac's theory.

This small difference was later called anomalous magnetic dipole moment of the electron.

This difference was later explained by the theory of quantum electrodynamics,

Developed by Shin-Itiro Tomonaga,

Julian Schwinger,

And Richard Feynman in the late 1940s.

With the development of the particle accelerator during the first half of the 20th century,

Physicists began to delve deeper into the properties of subatomic particles.

The first successful attempt to accelerate electrons using electromagnetic induction was made in 1942 by Donald Kirst.

His initial betatron reached energies of 2.

3 megaelectronvolts,

While subsequent betatrons achieved 300 megaelectronvolts.

In 1947,

Synchrotron radiation was discovered with a 70 megaelectronvolt electron synchrotron at General Electric.

This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light.

With a beam of energy of 1.

5 gigaelectronvolts,

The first high-energy particle collider was Adonay,

Which began operations in 1968.

This device accelerated electrons and positrons in opposite directions,

Effectively doubling the energy of their collision when compared to striking a static target with an electron.

The large electron-positron collider LAP at CERN,

Which was operational from 1989 to 2000,

Achieved collision energies of 209 gigaelectronvolts and made important measurements for the standard model of particle physics.

Individual electrons can now be easily confined in ultra-small CMOS transistors,

Operated at cryogenic temperatures over a range of 4 Kelvin to about 15 Kelvin.

The electron wave function spreads in a semiconductor lattice and negligibly interacts with the valence band electrons,

So it can be treated in the single-particle formalism by replacing its mass with the effective mass tensor.

In the standard model of particle physics,

Electrons belong to the group of subatomic particles called leptons,

Which are believed to be fundamental or elementary particles.

Electrons have the lowest mass of any charged lepton,

Or electrically charged particle of any type,

And belong to the first generation of fundamental particles.

The second and third generation contain charged leptons,

The muon and the tau,

Which are identical to the electron on charge,

Spin,

And interactions,

But are more massive.

Leptons differ from the other basic constituent of matter,

The quarks,

By their lack of strong interaction.

All members of the lepton group are fermions,

Because they all have half-odd integer spin.

The electron has spin one-half.

The invariant mass of an electron is approximately 9.

109 x 10-31 kg,

Or 5.

489 x 10-4 atomic mass units.

Due to mass-energy equivalence,

This corresponds to a rest energy of 0.

511 MeV.

The ratio between the mass of a proton and that of an electron is about 1,

836.

Astronomical measurements show that the proton-to-electron mass ratio has held the same value,

As is predicted by the standard model,

For at least half the age of the universe.

Protons have an electric charge of negative 1.

602176634 x 10-19 columns,

Which is used as a standard unit of charge for subatomic particles,

Also called the elementary charge.

Within the limits of experimental accuracy,

The electron charge is identical to the charge of a proton,

But with the opposite sign.

The electron is commonly symbolized by e-,

And the positron is symbolized by e+.

The electron has an intrinsic angular momentum,

Or spin,

Of bar h over 2.

This property is usually stated by referring to the electron as a spin-half particle.

For such particles,

The spin magnitude is bar h over 2,

While the result of the measurement of a projection of the spin on any axis can only be plus or minus bar h over 2.

In addition to spin,

The electron has an intrinsic magnetic moment along its spin axis.

It is approximately equal to 1 Bohr magneton,

Which is a physical constant equal to 9.

27400915 x 23 x 10-24 joules per tesla.

The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity.

The electron has no known substructure.

Nevertheless,

In condensed matter physics,

Spin-charge separation can occur in some materials.

In such cases,

Electrons split into three independent particles,

The spinon,

The orbiton,

And the holon,

Or chargeon.

The electron can always be theoretically considered as a bound state of the three,

With the spinon carrying the spin of the electron,

The orbiton carrying the orbital degree of freedom,

And the chargeon carrying the charge,

But in certain conditions they can behave as independent quasi-particles.

The issue of the radius of the electron is a challenging problem of modern theoretical physics.

The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity.

On the other hand,

A point-like electron zero radius generates serious mathematical difficulties due to the self-energy of the electron tending to infinity.

Observation of a single electron in a Penning trap suggests the upper limit of the particle's radius to be 10 to the negative 22 meters.

The upper bound of the electron radius of 10 to the negative 18 meters can be derived using the uncertainty relation in energy.

There is also a physical constant called the classical electron radius,

With the much larger value of 2.

8179 times 10 to the negative 15 meters,

Greater than the radius of the proton.

However,

The terminology comes from a simplistic calculation that ignores the effects of quantum mechanics.

In reality,

The so-called classical electron radius has little to do with the true fundamental structure of the electron.

There are elementary particles that spontaneously decay into less massive particles.

An example is the muon,

With a mean lifetime of 2.

2 times 10 to the negative 6 seconds,

Which decays into an electron,

A muon neutrino,

And an electron antineutrino.

The electron,

On the other hand,

Is thought to be stable on the theoretical grounds.

The electron is the least massive particle with non-zero electric charge,

So its decay would violate charge conservation.

The experimental lower bound for the electron's mean lifetime is 6.

6 times 10 to the 28th years,

At a 90% confidence level.

As with all particles,

Electrons can act as waves.

This is called the wave-particle duality,

And can be demonstrated using the double-slit experiment.

The wave-like nature of the electron allows it to pass through two parallel slits simultaneously,

Rather than just one slit,

As would be the case for a classical particle.

In quantum mechanics,

The wave-like property of one particle can be described mathematically as a complex-valued function,

The wave function,

Commonly denoted by the Greek letter psi.

When the absolute value of this function is squared,

It gives the probability that a particle will be observed near a location,

A probability density.

Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties.

In quantum mechanics,

This means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system.

The wave function of fermions,

Including electrons,

Is antisymmetric,

Meaning that it changes sign when two electrons are swapped.

Since the absolute value is not changed by a sign swap,

This corresponds to equal probabilities.

Bosons,

Such as the photon,

Have symmetric wave functions instead.

In the case of antisymmetry,

Solutions of the wave equation for interacting electrons results in a zero probability that each pair will occupy the same location or state.

This is responsible for the Pauli exclusion principle,

Which precludes any two electrons from occupying the same quantum state.

This principle explains many of the properties of electrons.

For example,

It causes groups of bound electrons to occupy different orbitals in an atom,

Rather than all overlapping each other in the same orbit.

In a simplified picture,

Which often tends to give the wrong idea but may serve to illustrate some aspects,

Every photon spends some time as a combination of a virtual electron plus its antiparticle,

The virtual positron,

Which rapidly annihilate each other shortly thereafter.

The combination of the energy variation needed to create these particles and the time during which they exist fall under the threshold of detectability expressed by the Heisenberg uncertainty relation.

In effect,

The energy needed to create these virtual particles can be borrowed from the vacuum for a period of time,

So that their product is no more than the reduced Planck constant.

While an electron-positron virtual pair is in existence,

The column force from the ambient electric field surrounding an electron causes a created positron to be attracted to the original electron,

While a created electron experiences a repulsion.

This causes what is called vacuum polarization.

In effect,

The vacuum behaves like a medium having a dielectric permittivity more than unity.

Thus,

The effective charge of an electron is actually smaller than its true value,

And the charge decreases with increasing distance from the electron.

This polarization was confirmed experimentally in 1997 using the Japanese Tristan particle accelerator.

Virtual particles cause a comparable shielding effect for the mass of the electron.

The interaction with virtual particles also explains the small deviation of the intrinsic magnetic moment of the electron from the Bohr magneton.

The extraordinarily precise agreement of this predicted difference with the experimentally determined value is viewed as one of the great achievements of quantum electrodynamics.

The apparent paradox in classical physics of a point-particle electron having intrinsic angular momentum and magnetic moment can be explained by the formation of virtual photons in the electric field generated by the electron.

Reviews

I love this guy’s soothing voice—works like a charm.💤

Very pleased to report that I know no more about electrons than I did in college, and I slept well! Thanks for another great recording, Benjamin!