Neutral carbon-12 (or any carbon atom) has 6 electrons with a total negative charge of 6e^- orbiting a nucleus with a total positive charge of 6e⁺, so that the total net charge is zero. The nucleus is made up of 6 protons, each with a positive charge of e⁺, and 6 neutrons, each with zero charge. The protons and neutrons have almost the same mass, and each is about 1800 times the mass of an electron. Counting up the total number of massive particles (protons and neutrons), we have 12, the atomic mass of C¹².