What is an Electron ?

"What is an electron ?" is a question that can be answered at various levels of detail and complexity, depending on the context. This page describes electrons at the the level required for high school chemistry (GCSE to A-Level in the UK).

Definition of an Electron:

An electron is a subatomic particle that has a negative charge of -1 and is located in the volume of atoms around the nucleus (so not in the nucleus itself)

Electrons have no known components or substructure and are therefore generally considered to be elementary particles.

Key Facts about Electrons

  • Electrons exist in the volume of atoms that surrounds the nucleus (see the diagram of an atom, on the right) 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.
  • An electron has a mass approximately 1/1836 of the mass of a proton, so a relative mass of 1/1836 ≈ 0.0005 ≈ zero.
    Electrons therefore account for very little of the total mass of the atom of which they are a part.
  • 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.
    Recall that the number of protons in an atom is the atomic number of that atom (element).

Questions about Electrons

  • When was the electron discovered ? and
    Who discovered the electron ?
    The electron was discovered in 1897 by British physicist J.J. Thomson who was working at the Cavendish Laboratory, Cambridge University. While his experiments in 1897, which led to evidence for the electron resulted in general recognition of this subatomic particle they were also the culmination of a series of experiments and results by many scientists working in different places.
    J.J. Thomson's Experiments leading to the discovery of the electron in 1897:
    J.J. Thomson carried out experiments which showed that the "cathode rays" were actually unique (and discrete) particles, as opposed to waves, atoms or molecules as had been postulated earlier. He calculated both the charge e and the mass m of an electron to good approximations and showed that the charge to mass ratio, e/m, of an electron was independent of the material used to make the cathode in his experiments.
  • Where does the word 'electron' come from ?
    The derivation (also known as "etymology") of the word "electron" is said to be from the word 'electric', combined with the suffix '-on', as in 'ion'.
    According to etymonline.com, the word 'electron' was first used in 1891 by Irish physicist George J. Stoney (1826–1911). Other sources credit Irish physicist George Francis FitzGerald (1851–1911).
  • What are electrons made/composed of ?
    (This is more advanced information that may not be required at school-level chemistry.)
    Electrons have no known components or substructure and are therefore generally considered to be elementary particles.
  • What is the opposite of an electron ?
    (This is beyond the scope of most school chemistry courses.)
    The antiparticle of the electron is called the positron. A positron is exactly the same as an electron except that it has the opposite charge/sign, so whereas an electron has a charge of -1, a positron has a charge of +1.

Why do I need to know about Electrons ?

It is important to know about electrons (for school level, e.g. GCSE Chemistry) because electrons are important for several key topics necessary for the understanding of basic chemistry. These topics include atoms, the electronic structure of atoms, ions, ionic bonding and covalent bonding. More generally, an understanding of electrons is important for many aspects of physics, such as nuclear physics, electricity, electronics, and semi-conductors.

See also the pages about What is an atom ?, What is a proton ? and What is a neutron ?

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