The nucleus lies at the center of the atom and consists of two types of particles, protons and neutrons. Almost all the mass of an atom is in the nucleus. Protons bear a positive electric charge. Electrons carry a negative charge, equal in magnitude and opposite to the charge of a proton. Protons and neutrons are nearly the same size and weight.
Atoms are extremely small, on the order of a few ten billionths of a meter.
An atom as a whole is electrically neutral. The positive nuclear core is surrounded by a negative cloud of electrons. A neutral atom has equal numbers of electrons and protons. Almost all nuclei contain roughly equal numbers of neutrons and protons. Since all nuclei contain protons, all nuclei are positively charged.