Diagram of the structure of the atom. An atom consists of one or more electrons that whirl about the tiny, central nucleus. The nucleus consists of protons (red) & neutrons (blue). The number of electrically positive protons balance the number of electrically negative electrons to make the atom neutral overall. Each proton & neutron consists of 3 quarks, bound together by the strong nuclear force. The proton is made of two up" quarks (dark blue) & 1 "down" quark (green). Neutrons are made of 2 "down" quarks & 1 "up" quark. The atom shown is beryllium, which has 4 electrons, 4 protons, & 5 neutrons (only 3 of which are shown)."