* Atomic Number: The number of protons in an atom's nucleus defines its atomic number. This number is unique to each element.
* Iron has 26 protons (atomic number 26).
* Sodium has 11 protons (atomic number 11).
* Element Identity: The atomic number is the fundamental characteristic that determines what element an atom is. Since iron and sodium have different numbers of protons, they are fundamentally different elements with distinct chemical and physical properties.
In summary: The number of protons is the core defining feature of an element. Any atom with 26 protons will always be an iron atom, and any atom with 11 protons will always be a sodium atom.
