sentence: Atoms are made up of electrons, neutrons, and protons.
sentences_after: The protons and neutrons are in the center of the atom, which is called the nucleus. The protons and neutrons are the heaviest part of the atom and make up most of its mass. The electrons move around the nucleus very quickly, making what is called an electron cloud. The electron cloud has a very small mass, but it makes up most of the space of the atom. The electrons have a negative charge, and the protons have a positive charge.
concept_name: atom
headings: Nuclear physics Atoms Structure