Atoms are known as the building blocks of matter. The name atom came from the Greek word atomos which means “not sliceable”. The idea of an atom was discovered by Greek philosophers Leucippus and Democritus who believed that there had to be a point in time where something could no longer be sliced. An atom is composed of protons, neutrons, electrons, and elementary particles. The atom’s center is called a nucleus, and within the nucleus protons and neutrons exist. Surrounding the nucleus is an electron cloud where electrons are found. Neutrons have no charge, protons are positive and define the atom, while electrons are negative and describe the behavior the atom exerts. Both protons and electrons are equal in magnitude despite having opposite charges, while neutrons are equal in mass to protons. Protons, neutrons, and electrons are known as neutral particles. There are other particles that make up an atom called quarks. There are six quarks, and they are called; up, down, strange, charm, bottom, and top. They are the composite particles that make up protons and neutrons, which in turn make up atoms.
“1.2 The Building Blocks of Matter.” College Physics, by Raymond A. Serway et al., 11th ed., Cengage Learning, 2018, pp. 3–4.