Question: At what point was the electron discovered?
About the article "Chemistry", section "Chemical structure".

Candidate passages:
The electron neutrino was discovered by Clyde Cowan and Frederick Reines in 1956. 
Clinton Joseph Davisson (October 22, 1881 – February 1, 1958), was an American physicist who won the 1937 Nobel Prize in Physics for his discovery of electron diffraction.
Davisson shared the Nobel Prize with George Paget Thomson, who independently discovered electron diffraction at about the same time as Davisson. 
At about the same time that Mendeleev organized the complexity of elements into a powerfully descriptive periodic table, work by Johann Hittorf and Eugen Goldstein began to investigate the existence of cathode rays.
Just prior to the beginning of the 20th century, J. J. Thompson and his colleagues identified the cathode rays as being composed as individual particles, and estimated their charge and mass.
The mass of that particle (the electron) was observed to be over a thousand times less than that of the atom, and this led Thompson to propose that matter was built from atoms that were essentially balls of positive charge with small, negatively charged electrons embedded inside.
This atomic model became known as the plum pudding model of the atom.
But less than 15 years later, an experiment was performed by Geiger and Marsden under the direction of Ernest Rutherford that showed evidence that a small positively charged nucleus was at the center of atoms.
This planetary model for the atom quickly replaced the older plum pudding model.
Shortly after the discovery of the nucleus, further experiments done by Rutherford showed that hydrogen nucleii could be forced out of heaver atoms in scattering experiments.
Hence, a positively charged particle, called the proton, was identified as a constituent of matter.
A series of experiments in the early 1930's discovered yet another type of penetrating substance that was originally thought to be a type of gamma ray, but in 1932 James Chadwick demonstrated that this new radiation was actually a neutral particle with a mass similar to that of the proton, and the new particle was named the neutron.
At this point things were again reduced to a very simple model, as the entire world was thought to be made up of atoms, each of which contained electrons, protons and neutrons.
The model was even simpler than the older fire, earth, air and water model of the ancients.
The electron, proton, neutron model had much more experimental rigor than the classical theories, and the new model led to a diverse array of elements.
For the most part, the science of what makes up matter was in a simple, well organized state.
Yet even at this time, it had already become known that there were a few particles in addition to the electron, proton and neutron.
Gamma rays had been discovered in 1900 by Paul Villard, and in 1932 Carl David Anderson discovered the positron, which is an antimatter equivalent of the electron.
But things quickly got far more complicated.
In 1936 Carl Anderson discovered a particle that was identical in every way to the electron except for mass, as it was about 200 times heavier.
But even more surprises were in store.
In 1955 the antiproton was discovered by Emilio Segre and Owen Chamberlain, and in 1956 the neutrino was discovered.
And throughout the 1950's a rather enormous number of different massive particles were discovered with the technology of particle accelerators and detectors.
By the end of the 1950's mankind's knowledge of what the world is made of had again grown to be very complex indeed.
Over time, the number of such particles became so large that it was termed a particle zoo.
It was clear by the early 1960's that the number of particles discovered was getting so large that there was likely some underlying pattern that could simplify our view of elementary particle physics. 
CUSB (Columbia University-Stony Brook) was a particle detector at the Cornell Electron Storage Ring.
CUSB, along with CLEO, confirmed the existence of the Υ(3S) and discovered the Υ(4S). 
In quantum chemistry, the electron localization function (ELF) is a measure of the likelihood of finding an electron in the neighborhood space of a reference electron located at a given point and with the same spin.
Physically, this measures the extent of spatial localization of the reference electron and provides a method for the mapping of electron pair probability in multielectronic systems.ELF's usefulness stems from the manner it allows the analysis of electron localization in a chemically intuitive way.
For example, the shell structure of heavy atoms is obvious when plotting ELF against the radial distance from the nucleus; the ELF for radon, for example, has six clear maxima, whereas the electronic density decreases monotonically and the radially weighted density fails to show all shells.
When applied to molecules, an analysis of the ELF shows a clear separation between the core and valence electron, and also shows covalent bonds and lone pairs, in what has been called "a faithful visualization of VSEPR theory in action".
Another feature of the ELF is that it is invariant with respect to transformation of the molecular orbitals.
The ELF was originally defined by Axel D. Becke and K. E. Edgecombe in 1990.
They first argued that a measure of the electron localization is provided by formula_1 where "ρ" is the electron spin density and "τ" the kinetic energy density.
"D" is expected to be small in those regions of space where localized electrons are to be found.
Given the arbitrariness of the magnitude of the localization measure provided by "D", it is compared to the corresponding value for a uniform electron gas with spin density equal to "ρ"(r), which is given by formula_2 The ratio, formula_3 is a dimensionless localization index that expresses electron localization with respect to the uniform electron gas.
In the final step, the ELF is defined in terms of "χ" by mapping its values on to the range 0 ≤ ELF ≤ 1 by defining the electron localization function as formula_4 ELF = 1 corresponding to perfect localization and ELF = ½ corresponding to the electron gas.
The original derivation was based on Hartree–Fock theory.
For density functional theory, the approach was generalized by Savin in 1992.
The approach of electron localization (not in this form) was pioneered by Bader.
Bader's analysis partitions the charge density in a molecule to "atoms" according to zero-flux surfaces (surfaces across which no electron flow is taking place).
Bader's analysis allows many properties such as multipole moments, energies and forces, to be partitioned in a defensible and consistent manner to individual atoms within molecules.
Both the Bader approach, and the ELF approach to partitioning of molecular properties have gained popularity in recent years, because the fastest, accurate ab-initio calculations of molecular properties are now mostly made using density functional theory (DFT), which directly calculates the electron density.
This electron density is the property whose properties are then analyzed using with Bader charge analysis or Electron Localization Functions.
One of the most popular functionals in DFT was first proposed by Becke, who also originated Electron Localization Functions.