xii.1. What’s inside an atom?
Protons, Neutrons and Electrons, which make up the atom in which Electrons are not further divisible. Electons are one type of elementary particle type under a broad category called Leptons. But what about the particles inside the nucleus, ie.Protons and Neutrons? Are they made up of still smaller particles? Yes, they are composite particles made of elementary particles. These elementary particles are called Quarks.
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Elementary (Fundamental) Particles of Matter – Quarks and Leptons |
Elementary particles occur in two basic types called quarks and leptons. There are 6 Quark types and 6 Lepton types. Together, Quarks and Leptons are part of a larger class known as Fermions. Fermions have spin like 1/2, 3/2, 5/2 etc. Quarks and Leptons are Fermions with 1/2 spin. |
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6 Quarks |
The six quarks are paired in the three generations – the “up quark” and the “down quark” form the first generation, followed by the “charm quark” and “strange quark”, then the “top quark” and “bottom (or beauty) quark”. The lightest and most stable particles make up the first generation, whereas the heavier and less stable particles belong to the second and third generations. All stable matter in the universe is made from particles that belong to the first generation; any heavier particles quickly decay to the next most stable level. Quarks also come in three different “colours” and only mix in such ways as to form colourless objects. |
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6 Leptons |
The six leptons are similarly arranged in three generations – the “electron” and the “electron neutrino”, the “muon” and the “muon neutrino”, and the “tau” and the “tau neutrino”. The electron, the muon and the tau all have an electric charge and a sizeable mass, whereas the neutrinos are electrically neutral and have very little mass. |
[Standard Particle Model]