What is an Electron?

In this article, we are going to learn about electron – how it was discovered, its properties, etc.

Table of Contents

• What is an Electron?
• Discovery of Electron
• Properties of Electrons

What is an Electron?

Electron is an elementary particle of nature, and the first one discovered by us. It’s an essential constituent of atom and molecules. In an atom, electron(s) revolve around the nucleus.

Modern Physics

Modern Physics, as the name suggests, is rather a new branch in physics. In other words, it’s a post-Newtonian conception of physics.

Here, we study about the elementary particles of nature, the structures they make, how they interact with each other, and fundamental forces of nature.

Discovery of Electron

The credit of the discovery of electron goes to J. J. Thomson. He considered them as fundamental and universal constituents of matter. In fact, the name “electron” was also given by Thomson. He was awarded the Nobel Prize in Physics in 1906 for this discovery.

After the discovery of electricity, many scientists conducted experiments on it towards the end of the 19th century. Most of these experiments involved conduction of electricity (i.e. electric discharge) through gases at low pressure in a discharge tube. This led to many new breakthroughs in science, the discovery of electron being one of the predominant one of them.

In the discharge tube, the gas is kept at a pressure of 10^-2 to 10^-3 mm of Hg, and a potential difference of 10⁴ V is applied between the electrodes (cathode and anode). This leads to:

• Electrons: A beam of electrons emerges from the cathode (so called cathode rays). J. J. Thomson was the first scientist to determine experimentally the speed and the specific charge [charge to mass ratio (e/m)] of the cathode ray particles. Cathode always emits electrons, no matter what material/metal is used as the cathode (emitter), or what gas is used in the discharge tube. This universality of the cathode ray particles was proved by the constant value of e/m, which is independent of the cathode material and gas.
• Positive ions: These are positively charged particles of the gas filled in the discharge tube (called Positive or Canal Rays). Goldstein discovered these rays.

Properties of Electrons

Electron beams (or Cathode rays) showcase the following properties:

• These are invisible to naked eye and travel in a straight line. However, in presence of electric and magnetic fields cathode rays (and also positive/canal rays) get deflected. It shows that electrons are electrically charged – to be specific, they have negative charge, which is denoted by e.
• Electron beams can ionise gases.
• Electron beams can also produce chemical change, e.g. they can affect a photographic plate. (Even positive/canal rays can produce physical and chemical changes, e.g. they can affect photographic plates, and produce phenomenon such as fluorescence and phosphorescence.)
• These beams produce X-rays when they strike a heavy metal (such as tungsten).

Charge of Electron

American physicist R. A. Millikan conducted his oil-drop experiment in 1913. The aim of this experiment was to measure the precise charge on an electron.

The results of the experiment showed that charge on an oil droplet was always an integral multiple of 1.602 × 10^-19 C. This is the elementary charge, which is the value of the charge on an electron. This is denoted by e. Every charged object in this world has a charge that is integral multiple of this value. So, this experiment proved that electric charge is quantised.

As scientists now knew the value of charge (e, calculated by Millikan) and specific charge (e/m, calculated by J. J. Thomson), the mass (m) of the electron could easily be determined.