The smallest particle that retains the properties of an element is an atom.
Quarks and leptons are just a family of elementary particles and do not carry any properties of the element.
Because the electron is a lepton, and is not made of quarks.
If the pure substance is not an element, the smallest part is a molecule (which is made of atoms) for instance, pure water is made of water molecules, which are made of 2 hydrogen atoms and 1 oxygen atom If the pure substance is an element, the smallest part is an atom. (which is made of Protons, Neutrons, and Electrons) Pure hydrogen is made of atoms. A stable hydrogen atom has 1 proton, 1 neutron, and 1 electron. Protons and Neutrons can be broken down further into Quarks, Leptons, and Bosons. The Electron is a type of Lepton.
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The wavelength of a lepton is inversely proportional to its momentum, which is related to its energy and mass. The spin of a lepton is a fundamental property intrinsic to the particle itself, independent of its momentum or wavelength.
Atoms can be broken down, so it is a quark or a lepton.
There is currently no scientific evidence for any constituents of an electron. So, for now, the electron is a lepton (a lepton is any fundamental particle).
Lepton
The lepton number of an electron is important in particle physics because it helps to determine the conservation of leptons in interactions. Lepton number is a fundamental property that must be conserved in particle interactions, and it helps to understand the behavior of particles and their interactions in the subatomic world.
The six leptons were discovered by the following:Electron: J J Thomson (1897),Electron nuetrino: predicted by Pauli (1930), discovered by Cowan-Reines (1956),Muon lepton: Carl D Anderson (1936),Muon neutrino: Lederman, Schwartz and Steinberger (1962),Tau lepton: Perl, (1974-1977),Tau neutrino: Fermilab (2000).
An antineutrino is a subatomic particle that is the antimatter counterpart of a neutrino. It has opposite properties, such as opposite electric charge and lepton number, compared to a neutrino. Neutrinos are neutral particles, while antineutrinos have a negative charge.
The principle of lepton number conservation states that the total number of leptons (such as electrons and neutrinos) must remain constant before and after a particle interaction. This principle helps to predict and understand the outcomes of particle interactions by ensuring that the total lepton number is conserved throughout the process.