At time we have . This yields our second basic equation. An atom consists of a compact and dense nucleus made up of neutrons and protons that is surrounded by lightweight electrons . The radius of an electron is 10E-10m. The atom is held together by the electrical attraction between the electrons.
Electrons appear to be point like particles called leptons .
They have no size or internal structure. Neutrons and protons appear to have size and contain elementary particles called quarks . Both leptons and quarks have an anti-particle version as well. Hydrogen has the simplest nucleus. It only has a single proton.