Discovery of Electron

As early as about 1830, electrical discharges in gases were intriguing a number of experimental physicists in Europe. In 1881, at the Cavendish Laboratory at the University of Cambridge, J.J.Thomson began experimenting with gaseous discharges, and continued to do so for the next 50 years. When Thomson started his research, cathode rays had already been known for about 50 years, but their nature was controversial. As Thomson later wrote in the paper reporting his discovery of the electron, "The most diverse opinions are held as to these rays; according to the almost unanimous opinion of German physicists they are due to some process in the ether to which. no phenomenon hitherto observed is analogous; another view of these rays is that, so far from being wholly ethereal, they are in fact wholly material, and that they mark the paths of particles of matter charged with negative electricity."

The German physicist Johann Wilhelm Hittorf studied electrical conductivity in rarefied gases: in 1869, he discovered a glow emitted from the cathode that increased in size with decrease in gas pressure. In 1876, the German physicist Eugen Goldstein showed that the rays from this glow cast a shadow, and he dubbed the rays cathode rays. 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 that the luminescence rays appearing within the tube carried energy and moved from the cathode to the anode. 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 what he termed 'radiant matter'. He suggested that this was a fourth state of matter, consisting of negatively charged molecules that were being projected with high velocity from the cathode

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 level of current, 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 a thousand times greater than what was expected, so little credence was given to his calculations at the time.

Key Facts about Electrons

• Electrons exist in the volume of atoms that surrounds the nucleus and not in the nucleus of atoms - which is where the protons and neutrons are located.

• Electrons are therefore subatomic particles but they are not nucleons.

• Electrons have a negative charge of -1.

• The number of electrons in an atom is the same as the number of protons in the atom. That is because atoms are charge neutral, and protons have a charge of +1 while electrons have a charge of -1 so there must be the same number of each in order for the whole atom to be charge neutral.

Electron counting methods

Identify the following:

Group number of the metal center.

Number of electrons contributed by the ligands.

Overall charge of the metal-ligand complex.

If the presence of metal-metal bond, one electron is counted towards each metal center in a bond.

Importance of Electrons

Electrons are important for the bonding of individual atoms together. in the obsence of this bonding force between atoms matter would not be able to interact in the many reactions. This interaction between the outer electron layers of an atom is call atomic bonding.

Atom has equal numbers of electrons and protons

An atom contains equal numbers of protons and electrons. Since protons and electrons have equal and opposite charges. This makes the atoms overall neutral.

Movement in electrons