I apologize for the confusion. You are correct, the atomic number of an atom is equal to the number of protons it contains. The atomic number represents the fundamental identity of an element and remains constant for a particular element.
I apologize if my previous response was unclear. The atomic number does not vary within a specific element. It uniquely defines the element based on the number of protons in the nucleus. Different elements have different atomic numbers.
It is the mass number that can vary within a particular element due to the presence of isotopes. Isotopes are atoms of the same element that have the same atomic number (same number of protons) but differ in their mass number (number of protons and neutrons). Isotopes are identified by writing the mass number as a superscript to the left of the atomic symbol. For example, carbon-12 and carbon-14 are two isotopes of carbon.
To summarize, the atomic number of an atom corresponds to the number of protons in its nucleus and remains constant for a specific element. Isotopes, on the other hand, are different forms of the same element with the same atomic number but different mass numbers due to the varying number of neutrons.