An atomic structure diagram is a visual representation of an atom, showing its nucleus (containing protons and neutrons) and its electron shells. These diagrams help us understand the arrangement of subatomic particles within an atom and make it easier to visualize the structure of different elements. The number of protons determines the element, while the number of electrons in the outermost shell helps explain its chemical reactivity. For example, the atomic structure of a carbon atom (atomic number 6) can be shown with 6 protons and 6 neutrons in the nucleus, and 2 electrons in the first shell and 4 electrons in the second shell.