Almost all the mass of an atom is due to the nucleus. The nucleus lies at the center of the atom and consists of two types of particles, protons and neutrons. The nucleus of the smallest atom, the commonest form of hydrogen, consists of a single proton and no neutrons. All other nuclei contain neutrons as well as protons. Protons bear a positive electric charge.
Neutrons are electrically neutral.
Since all nuclei contain protons, all nuclei are positively charged. Nuclei contain roughly equal numbers of neutrons and protons. Protons and neutrons are nearly the same size and weight. An atom as a whole is electrically neutral. This is because the positive nuclear core is surrounded by a cloud of negative particles called electrons.