Final answer:
Atom diagrams vary based on the number of protons, neutrons, and electrons. Key differences between isotopes are the number of neutrons. Electron shells influence chemical properties and stability of atoms.
Step-by-step explanation:
Atom diagrams vary primarily based on the subatomic particles they contain: protons, neutrons, and electrons. Every element is defined by the number of protons in its nucleus, also known as the atomic number. For instance, all atoms of hydrogen have one proton, while all atoms of iron have 26 protons. This fundamental characteristic makes each element chemically unique.
The key distinction between isotopes of the same element lies in the number of neutrons. Isotopes have the same number of protons but differ in the number of neutrons. For example, the three isotopes of hydrogen are protium with no neutrons, deuterium with one neutron, and tritium with two neutrons, yet they all have one proton.
Electrons occupy energy levels known as electron shells. The distribution of electrons across these shells determines an atom's chemical properties and its stability. Reactive elements have incomplete outer shells, which makes them more likely to participate in chemical reactions to achieve stability, often by forming compounds.