An atom is made up of protons and neutrons (both found in the nucleus) and electro (irl the surrounding electron cloud), The atomic number i$ erupt to th e bomber of pr The mass number is equal to the plumber protons plus neutirons, in a neutral atom . number of protons equals tho number of electrons. The charge on an ion indicates ( ,moalance between protons and electrons. Too many electrons produc .-marge. too positive charge. 'hls structure Carl be wriitern as part of a chemical symbol.