The Discovery of the Electron

The idea of atoms existing was put forward by the famous Ancient Greek philosopher Democritus who thought that everything around us was made up of minuscule particles.
Democritus thought that by cutting an object could he could continue cutting it continuously. He concluded that this was not possible as there would be a piece that would be far too small to cut. Democritus also thought that these very small pieces (particles) were the basic building blocks of everything around us.

The word ‘atom’ comes from the Greek word ‘atomos’.
In the beginning of the 19th century John Dalton showed that atoms actually existed. He found out that there were atoms for every single element in the periodic table. During this time they did experiments with electric currents. These experiments involved obtaining the electric current and passing it through a gas.

In the 19th these scientists built glass tubes which had metal contacts on each end and got rid of most of the air in the tube and put an extremely high voltage between the metal contacts. If there was a wire between the metal contacts the electric current would have flowed through the wire, however the current had to go through the small quantity of gas still in the glass tube, and this caused powerful and spectacular arrays of glowing lights.
What happened was electric currents were being forced through the gas which was hitting the atoms of the gas which shook them to form light.

As technology improved better vacuums were made which were capable of getting rid of all the gas in glass test tubes. JJ Thompson passed an electric current through the vacuum which hit the glass and created a small green speck. When Thompson used magnets the green speck would move and also when he applied a voltage to the glass tube the speck would move again. Also when he used both of them at the same time the speck would stay still (he balanced the electric and magnetic force).

JJ Thompson was head of the ‘Cavendish Laboratory’ in Cambridge where he carefully studied the electrical beam which is known as a ‘cathode ray’. In the modern era the ‘Cavendish Laboratory’ has all the equipment that Thompson ‘apparently’ used for his experiments including the ones which he used to discover the electron. The word ‘apparently’ is used because he was not necessarily good at carrying out experiments.

On one of the apparatus there is a small disk made of metal where electrons were emitted. At first Thompson was unsure what this beam of light was, so he changed the material of the cathode to see if it was the property of cathode material. He also changed the number of gas particles in the glass tube. However each time he changed the variables of the experiment he still saw the green light, this meant that this was caused by the property of the matter not the material.

This concluded that these are charges of negative electricity which was carried by particles of matter.

Although Thompson had influenced the discovery of the electron, there were other scientists who were carrying out a similar experiment. In Berlin a German physicist was doing a more effective experiment unfortunately he misinterpreted his results. He thought that the beams of light in his tube were the flow of matter however he did not think that these were individual particles.
The electron was discovered in 1897.

Soon after the electron was discovered an American physicist Robert Millikan was able to calculate the electron’s charge and mass. He found out that the electron has a negative charge and was about 2000 times lighter than the smallest atom.

JJ Thompson thought that if there are electrons which have a negative charge in an atom then there must be a positive charge as well to counteract the negative charge. He put forward his idea of the ‘plum pudding model’. This meant that the electrons were meant to be surrounded by a circle of positive matter. This was what people thought the atom looked like towards the end of the 19th century.
However this idea was altered by Ernst Rutherford who came from New Zealand. In 1907 at Manchester Rutherford set up a famous experiment, this was where a small machine would expel (shoot) out alpha particles which would come into contact with a very thin foil of gold. Rutherford discovered that 1 in 8000 alpha particles were deflected back from the gold foil. Alpha particles are large and positively charged. This means that the alpha particles have hit a positive atom in the gold foil which causes them to be repelled.

Rutherford though that these atoms must have had a positive centre. After several experiments involving many different kinds of atoms Rutherford concluded that the atom consisted of a positive nucleus with negative electrons on the outside. This idea was similar to a solar system with the electrons orbiting the nucleus at the centre; this means that atoms are mostly empty space.

Electrons are loosely attached to the atom. This is important for technology which makes the electron the most useful subatomic particle. The electron can be useful for motors and electricity.

In 2008 a group of scientists from Sweden recorded the electron in motion which happens to be similar like a hummingbird flapping its wing.
The human understanding of electrons has allowed us to improve our technology and produce items such as computers and lasers.

This experiment could allow us to see inside electrons and molecules which would give us tools such as controlling a chemical reaction.

The atom has ‘sub-structure’ and we can fill its inner workings. Electrons are fundamental particles, but protons and neutrons are not. Protons and neutrons are composed of smaller particles known as quarks.

Thank you for reading.