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A Brief Introduction to Leptons

Updated: Jun 23, 2020

By Oleksandr Koliakin

After you have read about quarks, you might think that everything is made out of quarks. That is not the case. Baryons usually make up the nuclei of atoms. Protons and Neutrons are baryons. There are tons of baryons apart from protons and neutrons, such as the Lambada or the Xi. There are also particles called mesons which are made of a quark and an anti quark. (To read more about anti quarks visit “Antimatter“ posts.) We will talk about baryons and mesons in a different post. Electrons however, are not baryons.

First let’s look at the basic properties of electrons. Electrons are about 1800 times smaller than protons and an electron has about 2000 times smaller mass than a proton! However, an electron still has a negative charge equal to the positive charge of a proton. Electrons are held in orbit around a proton by exchanging particles of the electromagnetic force: photons.

Electrons are what scientists call leptons. There are six known kinds of leptons, split into three categories called generations of matter. Each generation of matter consists of two types of leptons, charged and neutral. A charged particle is a particle with a charge, either negative or positive, while a neutral particle is a particle without a charge.

The charged lepton in the first generation of matter is the electron. Its uncharged partner is called an electron neutrino. The charged particle of the second generation of matter (for leptons) is the muon and its uncharged partner is called the muon neutrino. The charged particle of the third generation of matter (for leptons) is the tau and its uncharged partner is called the tau neutrino.

In an atom, charged leptons usually orbit a nucleus made out of baryons. Usually the nucleus is made out of protons and neutrons and the leptons orbiting the nucleus are usually electrons. However, it is theoretically possible for the protons and neutrons to be replaced by other baryons and the electrons to be replaced by other leptons. These atoms are called exotic atoms. Theoretically, many different kinds of exotic atoms exist. They are so interesting and there is much to cover about them, so they will be discussed in a different post.

Complete the "leptons" quiz


  • "A Brief History of Time" by S. Hawking

  • "SCIENCIA" (book)

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