The mass of an element discharged at an electrode m is directly proportional to the amount of electrical charge Q passed through the electrode.
If the same amount of electrical charge Q is passed through several electrodes, the mass m of an element discharged at each electrode will be directly proportional to both (a) the atomic mass of the element, and (b) the number of moles of electrons required to discharge one mole of the element from whatever material is being discharged at the electrode (the charge number z).
HISTORY
During the 19th century, chemists and physicists lived in a golden age of discovery. Some major breakthroughs in understanding the electron were made with amazing regularity. There were many great scientists of the time including Michael Faraday and Ernest Rutherford, who undertook remarkable and significant research. The idea of a basic indivisible building block, the atom was well known to them. The idea of a basic indivisible building block, the atom, had been proposed as far back as 5th century BC by Democritus. It was only at the end of the 19th century that Rutherford and Thomson were starting to show that the atom was made up of smaller building blocks.
By the end of the century so much was happening so quickly in the world of science that hardly a month went by without some new discovery. A number of scientists had noticed that when an electric charge was passed through a tube containing gas at low pressure, rays appeared from one of the electrodes. These cathode rays, as a German physicist, Eugen Goldstein, called them, were the source of much debate. A frenchman, Jean Perrin, showed that the rays carried a negative charge.
However, it took a Briton, Joseph John Thomson to make what is possibly the greatest discovery in the history of physics. He discovered the electron. Working in the Cavendish Laboratory at Cambridge, Thomson conducted a series of experiments - first reported on in 1897 - which were to change our view of the atom forever. Thomson's glass tube held a better vacuum than his rivals, and he was able to prove that cathode rays were deflected by both magnetic and electric fields.
Thomson then set about measuring the mass of these particles and to his astonishment found that they weighed almost 2,000 times less than a hydrogen atom, which at that time was thought to be the lightest matter in the universe. Atoms were clearly not the fundamental building blocks!
The discovery of the electron paved the way for other chemists and physicists to examine the atom in more detail and by 1911 Ernest Rutherford realised that the electrons in an atom were orbiting a central core, which was positively charged. Two years later, the great Danish physicist Niels Bohr developed atomic structure to the level we are familiar with today, where electrons move around the nucleus in specific patterns.
MICHAEL FARADAY (1791-1867)
Faraday is often referred to as the "father of electricity" because of the importance of his scientific discoveries, the principals of which are still used today in the production and supply of electricity.
It was in 1831 that Michael Faraday plunged a bar magnet into a coil of wire and first recognised that he had generated, in his own words, "a wave of electricity".He later rotated a copper plate between the poles of a magnet and found that power could be taken from the axis to the rim of the disc.
These fundamental experiments provided the basis for the production of electrical power by mechanical means.
JOSEPH JOHN THOMSON (1856-1940)
Thomson is considered the discoverer of the electron through his experiemtns on the stream of particles (electrons) emitted by cathode rays.
A theorist as well as an experimenter. He advanced the "plum-pudding" theory of atomic structure in 1898, holding that negative electrons were like plums embedded in a pudding of positive matter.
He was awarded the 1906 Nobel proze in physics for his work on the conduction of electricity through gases, was knighted in 1908 and received the order of merit in 1912.
Thomson was awarded the 1906 Nobel Prize in physics for his work on the conduction of electricity through gases.
He began work in the Cavendish Laboratory in 1880 under Lord Rayleigh, the second Cavendish Professor, and, when Rayleigh resigned the Cavendish chair in 1884, Thomson was elected to it, despite the fact that he was only 28 at the time, and was known more for his mathematical ability than for his skill in experimental physics.
He started experiments on the discharge of electricity through gases at low pressure, a subject which he pursued for the rest of his working life. It led to the discovery of the electron in 1897, one of the most significant events in science.
Under Thomson's leadership the Cavendish Laboratory continued to make fundamental discoveries. Thomson's further work on gas discharges led to Aston's mass spectrometer, and the discovery of isotopes. Thomson received the Nobel Prize in 1906 for his theoretical and the experimental researches on the discharge of electricity through gases! He was the president of the Royal society from 1915 until 1920 and the master of Trinity from 1918 until his death on August 30 1940.
