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The Electron




The electron is a subatomic particle (or fundamental particle - the smaller particle composing atoms and it cannot be broken down into smaller parts). In an atom the electrons surround the nucleus which is composed of protons and neutrons in an electron configuration (the arrangement of electrons of an atom).

The word electron was coined in 1894 by Johnstone Stoney (an Irish physicist) and is derived from the Latin electrum or the Greek elektron meaning amber (fossilized tree resin). Electrostatic charge can be generated by rubbing amber with wool and it is done for demonstrating the electrostatic charge phenomena to elementary students.

Electrons have a negative electrical charge and when they move, they generate an electric current.

Electrons are very small and have a mass of 9.11 × 10-31 kg, which is approximately 1/1836 of the mass of the proton; its radius is 2.8179 × 10-15 m., and it has a negative electric charge of -1.6 × 10-19 coulombs.

Atoms play an important role in chemistry since the electrons of an atom determine the way in which atoms interact with other atoms (chemical reactions) and this process is behind the chemical properties of the different materials.

The electron as a unit of charge was established by Johnstone Stoney in 1874 which also invented its name as mentioned above.

The discovery that the electron was a subatomic particle was made in 1897 by J. J. Thomson at the Cavendish Laboratory at Cambridge while he was studying cathode rays. Influenced by Maxwell, and the discovery of the X-rays by Röntgen, he deduced that cathode rays existed and were negatively charged particles.

The periodic law states that the chemical properties of elements repeat themselves periodically as seen in the periodic table of the elements. Many not satisfying explanations were suggested at the time for this until in 1913 when Henry Moseley introduced the concept of the atomic number and explained the periodic law with the number of protons each element has in its nucleus. In the same year, Niels Bohr showed that actually the electrons and not protons are behind the periodic table behavior. In 1916, Gilbert Lewis and Irving Langmuir went further and explained the chemical bonding of elements by electronic interactions.

In a simplistic way, it's possible to say that electrons in an atom exist in a number of electron shells surrounding the nucleus and they move there (when the element is stable). Each electron shell is given a number 1, 2, 3, and so on, starting from the one closest to the nucleus. Each shell can hold up a maximum number of electrons. The distribution of the electrons in the shells is called electron configuration.

Elements with complete outer shells, with maximum electrons possible, are less reactive. Elements with outer shells with less than maximum electrons are more reactive.

The motion of the electron around the nucleus is a controversial topic. It's not possible to say that electrons exhibit motion in the physical sense of the word. Rather, the electron seems to appear in and out of existence at various points around the nucleus and we cannot predict the exact position of an electron. This is of course is a tricky idea and explained further by the Heisenberg uncertainty principle (quantum mechanics).

The electron belongs to a class of subatomic particles called leptons (fundamental constituents of matter) which are fundamental particles. The word "particle" is tricky because quantum mechanics shows that electrons also behave like a wave - this phenomena is called wave-particle duality.

Electron microscopes magnify up to 600,000 times.



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Last updated: April 2011
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